First megafloristic record for the Chubut Group at Somuncurá-Cañadón Asfalto Basin: An angiosperm dominated flora from the Upper Cretaceous Puesto Manuel Arce Formation, Patagonia Argentina

Cretaceous Research 56 (2015) 200e225

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First megafloristic record for the Chubut Group at Somuncura ~ ado
n Asfalto Basin: An angiosperm dominated flora from the Can Upper Cretaceous Puesto Manuel Arce Formation, Patagonia Argentina
ez c Mauro G. Passalia a, b, *, Magdalena Llorens a, c, Manuel Pa
gicas, Argentina Consejo Nacional de Investigaciones Científicas y Tecnolo Instituto de Investigaciones en Biodiversidad y Medioambiente, CONICET-UNCo, S.C. de Bariloche, Argentina c
n Nacional de Energía Ato
mica (CNEA), Regional Patagonia, Trelew, Argentina Comisio a

b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 1 December 2014 Accepted in revised form 30 April 2015 Available online 2 June 2015


-Can ~ ado
n Asfalto The first association of fossil plant impressions in the Chubut Group at the Somuncura Basin is described herein. The mid-Cretaceous megafloral assemblage from Patagonia, Argentina was recovered from the Puesto Manuel Arce Formation. The taphocenosis consists mostly of leaves preserved as impressions, although a variety of cuticle remains are also present. Angiosperms are both quantitatively and qualitatively the main component of the flora (at least 9 leaf morphotypes recognized). A few ferns and conifers complete the plant assemblage. The angiosperm leaves exhibit physiognomic heterogeneity with a variety of well-defined venation patterns. The myrtophyll morphotype (Myrtoidea sp.) and palmatilobed palinactinodromous leaves (Bamfordphyllum crassivena gen. et sp. nov.) are significant components of the assemblage. Flora characters are consistent with the Cenomanian e earliest Turonian age proposed for the Puesto Manuel Arce Formation. Comparisons were made with coeval Patagonian and extra-regional floras which suggest both local as well as long-distance Gondwanan links. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Cretaceous Angiosperm Patagonia Chubut Group Puesto Manuel Arce Formation

1. Introduction The mid-Cretaceous was an important period in the evolution of angiosperms with a rapid increase in their diversity and relative abundance in plant communities. Floras dominated by conifers and ferns shifted to being dominated by flowering plants (Lidgard and Crane, 1990; Lupia et al., 1999; Coiffard et al., 2006). By the midCretaceous, the angiosperms had begun their adaptive radiation and major extant lineages at the level of subclass, order and probably some families made their first appearance (Upchurch and Dilcher, 1990). Particular angiosperm taxa began to occur more frequently especially around the CenomanianeTuronian boundary (Boulter et al., 1998). The origin and different stages in the diversification of flowering plants during the Cretaceous in southern South America have been the subject of many studies (i.e. Romero and Arguijo, 1981; Romero

* Corresponding author. Instituto de Investigaciones en Biodiversidad y Medioambiente, CONICET-UNCo, S.C. de Bariloche, Argentina. E-mail addresses: [email protected] (M.G. Passalia), magdalena.llorens@
ez). gmail.com (M. Llorens), [email protected] (M. Pa http://dx.doi.org/10.1016/j.cretres.2015.04.016 0195-6671/© 2015 Elsevier Ltd. All rights reserved.

and Archangelsky, 1986; Papú, 1989; Romero, 1993; Passalia et al., 2001; Llorens, 2003; Cúneo and Gandolfo, 2005; Gandolfo and Cúneo, 2005; Quattrocchio et al., 2005; Barreda and
ez Archangelsky, 2006; Iglesias et al., 2007; Passalia, 2007; Narva and Sabino, 2008; Povilauskas et al., 2008; Puebla, 2009; Vallati, 2010, 2013; Perez Loinaze et al., 2012; Archangelsky and Archangelsky, 2013; Povilauskas, 2013). Most of these Cretaceous records are concentrated in two time intervals: the Aptian (late Barremian?) to mid-Cenomanian, and the Campanian to Maas
mparo, 2012). No palynotrichtian (Archangelsky et al., 2009; Pra logical records are available for the TuronianeSantonian in southern South America. However, certain angiosperm pollen forms are present in both the lower and uppermost Cretaceous intervals mentioned above, suggesting continuity through the TuronianeSantonian (Archangelsky et al., 2009). In contrast, two angiosperm megafloral assemblages provide evidence of flowering plants during the TuronianeConiacian, one being the CenomanianeConiacian Mata Amarilla Formation of the Austral Basin (i.e. Iglesias et al., 2007), and to the other the upper Turonianelower Coniacian Portezuelo Formation, Neuquen Basin (Passalia et al., 2008).

M.G. Passalia et al. / Cretaceous Research 56 (2015) 200e225

Further evidence of CenomanianeSantonian floras from southern South America is critical for understanding of the transformation of plant communities toward angiosperm dominated floras. This communication describes the first megaflora from the Cenomanian (to lowermost Turonian?) Puesto Manuel Arce For
e mation (Chubut Group) which crops out in the Somuncura ~ ado
n Asfalto Basin helps fill this gap (Figs. 1e3). With exception Can of a single megaspore included in a charophyte assemblage (Gamerro, 1977; Musacchio, in Chebli et al., 1976), there are no other previous plant records for this unit. The Chubut Group is widely recognized for its large areal extent, which spans two depocenters, and for its fossil record, which is composed mainly of vertebrate remains (i.e. Rich et al., 1998; Novas et al., 2005; Gaffney et al., 2007; Carballido et al., 2011; De la Fuente et al., 2011). In contrast, the paleobotanical record is sparse and restricted to the Golfo San Jorge Basin. It consists of a few megafloral remains that include angiosperm leaves from the middle Albianelower Cenomanian Castillo Formation (i.e. Frenguelli, 1930;
ndez, 1959) and araucariaceous woods from the Cenomanian Mene Bajo Barreal Formation (Pujana et al., 2007). Chebli (1973) also mentioned the presence of sphenopterid fronds in a level from the Laguna Palacios Formation (mid-Cenomanian). Palynological studies of the Chubut Group include assemblages from outcrops of Pozo D-129 Formation (Aptian) and ~ ado
n Seco (¼Bajo Barreal Formation, subsurface deposits of Can Cenomanian) (Archangelsky et al., 1994; Vallati, 2013). Moreover,
-Can ~ ado
n Asfalto Basin, the palynological record in the Somuncura of the Chubut Group is restricted to subsurface assemblages of the lower Albian Los Adobes Formation (Marveggio and Llorens, 2013) and an unpublished report from the Albian-mid Cenomanian Cerro Barcino Formation (Pothe de Baldis, 1976 in Page, 1987). Other floristic assemblages from Upper Cretaceous geological units in the Chubut Province include megafossils and palynological data assigned to the CampanianeMaastrichtian (i.e. Gandolfo and Cúneo, 2005; Cúneo et al., 2013; Hermsen et al., 2014), while palynological associations have been described from the Campanianelower Maastrichtian Paso del Sapo Formation (Papú, 1989)
n Formation and the overlying MaastrichtianeDanian Lefipa (Baldoni, 1992; Baldoni and Askin, 1993; Barreda et al., 2012). The aim of this study is to describe the first assemblage of fossil
-Can ~ ado
n plant impressions for the Chubut Group in the Somuncura Asfalto Basin. This flora is derived from the Upper Cretaceous Puesto Manuel Arce Formation.

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2. Geology and age The Chubut Group consists of Cretaceous continental sediments with abundant pyroclastic input (i.e. Codignotto et al., 1979; Figari et al., 2002). Outcrops are extensive and span two depocenters
within a basin whit an irregular morphology, the Somuncura ~ ado
n Asfalto in the north (Cortin ~ as, 1996) and the Golfo San Can Jorge in the south, covering a large part of the Chubut Province and northern Santa Cruz Province as well as extending onto the continental shelf (Fig. 1). Each depocenter has a formal stratigraphic order for the Group, and the geographic boundary between them is the Sierra Cuadrada mountain range, from which the fossil material reported on here was recovered, and the adjacent Meseta del Canquel. Within the Golfo San Jorge Basin, the units arranged from base to top are: Pozo D-129, Matasiete, Castillo, Bajo Barreal and ~ ado
n Asfalto Laguna Palacios formations. For the Somuncur
a-Can Basin, based on Anselmi et al. (2004), who elaborated the geological chart of the area, the recognized units from base to top are: Los Adobes, Cerro Barcino and Puesto Manuel Arce formations (Fig. 3B). The stratigraphic arrangement into these formations is discussed in depth with a synopsis of the different proposals by Marveggio and Llorens (2013). The Puesto Manuel Arce Formation (Chebli et al., 1976) concordantly overlies the Cerro Barcino Formation, while its top is marked by the presence of erosive channels of the Salamanca Formation (Fig. 2CeD). Codignotto et al. (1979) and Panza (1981) suggested that Puesto Manuel Arce it should be regarded as a member of the
s, 1988) Cerro Barcino Formation. More recent treatments (e.g. Corte maintain the formation rank as initially proposed by Chebli et al. (1976) and we follow this here. The Puesto Manuel Arce Formation was described by Chebli et al. (1976) as a succession of conglomerates, sandstones and clays from whitish to greenish in the lower section, while the upper section is composed of alternating varicolored clays and silts. The sedimentary environment is interpreted as a fluvial system of moderate to high energy that transitions into low energy lacustrine environments, with a sporadic pyroclastic input throughout all the sequence. The samples studied come from a facies association mainly from the lacustrine origin and with thin fluvial facies interbedded. The first are composed by siltstones with parallel lamination, while the last one, by tuffaceous sandstones. It crops out at both DE1 and DE2 locations, immediately below a conglomerate that represents the beginning of Salamanca Formation deposition by means of an erosive unconformity. The fossiliferous levels correspond to the lowermost upper section of the Puesto Manuel Arce Formation at

~ ado
n Asfalto Basin. B. Detail of the Sierra Cuadrada area (arrow in A) based on the geological survey of Fig. 1. A. Map showing the approximate limits of the Golfo San Jorge/Can Anselmi et al. (2004). Asterisk denotes the sampling area.

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Fig. 2. A. View toward south of the north flank of the Sierra Cuadrada showing the fossiliferous localities (arrows) Estancia Don Eduardo 1 (DE1) and 2 (DE2). B. Detail of Cretaceous to Neogene outcrops recognized in the area. In this zone, the Puesto Manuel Arce Formation overlies concordantly the Cerro Barcino Formation (Albian-lower Cenomanian) and is incised by laterally continuous banks of coarse sandstones to fine conglomerates belonging to the Paleocene (Danian) deposits of Salamanca Formation. Large areas are covered by Neogene basalt flows (Basalto Sierra Cuadrada). C. Detail of Estancia Don Eduardo 1 locality (DE1). Arrow indicates the fossiliferous level. D. Detail of the plant bearing level at Estancia Don Eduardo 2 locality (DE2), covered by a conglomerate bank of Salamanca Formation.

the top of the Chubut Group (Fig. 3A), at few meters above a guide stratum of silicified tuffs. The age of the Chubut Group is controversial and only in recent years have there been contributions from contemporary dating. Many authors have considered a ValanginianeLate Cretaceous age ~ as, 1996), or with the (i.e. Barcat et al., 1989; Proserpio, 1987; Cortin base begining in the ValaginianeHauterivian (Lesta and Ferello, 1972). These estimations were made based on stratigraphic relationships and scarce paleontological data. Figari and Courtade (1993) proposed an age of BarremianeCampanian for the Chubut ~ ado
n Group based on a biostratigraphic study of the underlying Can Asfalto Formation made by Masiuk (in Figari and Courtade, 1993).

~ ado
n Asfalto There, Masiuk considered that the upper section of Can should be included in a Cretaceous sedimentary series (BerriasianeHauterivian in age). Therefore, this implies an age not older than late Barremian for the base of the Chubut Group. A study of
-Can ~ ado
n Asfalto paleomagnetism in the area of the Somuncura Basin shows a normal orientation of the crystals in the samples taken in Los Adobes and Cerro Barcino formations, which lies
n Cretaceous ranging from Aptian to within the normal supercro Campanian (Geuna et al., 2000). Thus, the BerriasianeBarremian age were discarded for the base of the Chubut Group. A recent study of Marveggio and Llorens (2013) suggests that the deposition of the ~ ado
n Asfalto Basin began Chubut Group in the Somuncur
a-Can

M.G. Passalia et al. / Cretaceous Research 56 (2015) 200e225

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during the earliest Albian (or latest Aptian) based on the presence of angiosperm tricolpate pollen in a palynological assemblage from the Los Adobes Formation. The Puesto Manuel Arce Formation, which has yielded the plant fossils herein, was given several imprecise ages. Chebli et al. (1976) proposed an age as young as Maastrichtian based on similarities of ostracodes, charophytes and megaspores with those from the Up
n Group. Page et al. (1999) per Cretaceous deposits of the Neuque suggested a Campanianeearly Maastrichtian age based on a proposed conformable contact with the overlying upper MaastrichtianeDanian Salamanca Formation. Five Late Cretaceous Ar/Ar ages ranging between 97.9 and 85.1 Ma were given for the upper Chubut Group at San Jorge Basin (Bridge et al., 2000), but the
rez et al. analytical data to support them are lacking. Recently Sua (2014) obtained high precise U/Pb zircon ages that constrain the Puesto Manuel Arce Formation to the Cenomanian (97.4 ± 0.8 Ma), in 15 of 18 zircons analyzed, and just 1 gave an earliest Turonian (92.6 ± 1.5 Ma) age. 3. Materials and methods The fossils consist mainly of impressions and compressions of isolated leaves. They were collected at Estancia Don Eduardo, located on the north slope of Sierra Cuadrada, Chubut Province, Argentina (Fig. 1). Two plant-bearing lenses, here named Estancia Don Eduardo 1 (DE1) and Estancia Don Eduardo 2 (DE2), have been identified (Fig. 2), about 1.5 km distance apart. The angiosperm leaf impressions were described following the Manual of Leaf Architecture (Ellis et al., 2009). However some terminologies used such as those referring to the vein course or the relative thickness of veins were taken from Hickey (1973). Quotation marks indicate new fossil genera or species proposed exclusively in an unpublished dissertation or thesis (i.e. “Robustavena lobata”, “Crassidenticulum variloba”) and considered not validly published according to the International Code of Botanical Nomenclature of Melbourne (i.e. Arts. 29 and 30, specially Arts. 29.1, 30.8 and the Recommendation 30A.2, McNeill et al., 2012). Scarce cuticles are also preserved, one of them belonging to the conifer fossil genus Brachyphyllum, and were included in this study. The leaf cuticle was removed from the matrix with a brush and oxidized in 40% nitric acid for 5e10 min followed by 5% ammonium hydroxide for 2 min. For observation under light microscopy, the cuticle was mounted in glycerine jelly before examination. Specimens were observed using a Nikon SMZ800 stereomicroscope and photographed with a Sony DSC-H7 digital camera. Light micrographs were taken with a Nikon DS-Fi1 digital camera. Pictures and line drawings were improved with an image processor (Adobe Photoshop cs). All materials are stored at the Paleobotanical
gico Egidio Feruglio under the collection of the Museo Paleontolo initials MPEF-Pb-Mz. 4. Systematic palaeontology 4.1. The angiosperm component At least nine angiosperm taxa have been recognized. All of them consist of dicot leaves. Although a systematic position at Order level remains open, possible botanical affinities are discussed.

Fig. 3. A. Stratigraphic sections of Estancia Don Eduardo 1 and 2 (DE1 and DE2), showing the procedence of the fossil plants studied. B. Generalized stratigraphic
rez et al. (2014). Asterisks indicate U/ scheme of the Chubut Group modified from Sua Pb zircon ages obtained by Su
arez et al. (2014) from the Puesto Manuel Arce (97.4 Ma), Laguna Palacios (97.6 and 96.0 Ma) and Bajo Barreal (99.3 Ma) formations.

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Fig. 4. Myrtophyll dicot leaves from the Puesto Manuel Arce Formation. AeP. Myrtoidea sp. A (see also Fig. 4H) (MPEF-Pb-Mz 6747). B (see also Fig. 4I) (MPEF-Pb-Mz 6675). C (see also Fig. 4J) (MPEF-Pb-Mz 6672). DeE (see also Fig. 4KeL) (MPEF-Pb-Mz 6641). E. Detail of the leaf area marked by a white rectangle in Fig. D. White arrowheads indicate the development of a lateral vein admedially forked, resulting in two branches of quite similar gauge, that may be interpreted as two secondary veins as well as one of them a secondary and the other an intersecondary (see also black arrowheads in Fig. 4L). White arrows indicate secondary veins (see also black arrows in Fig. 4L). F. Detail of a leaf base with decurrent shape. Note the thin lamina extending on both sides of the short petiole and the massive gauge of the mid-vein (MPEF-Pb-Mz 6694). G. Detail of the leaf drawn in Fig. 4M showing

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Phyllum Magnoliophyta Cronquist, Takhtajan and Zimmerman ex Reveal 1995 Class Magnoliopsida (¼Dicotyledoneae) Cronquist, Takhtajan and Zimmerman ex Reveal 1995 Order incertae sedis

4.1.1. Myrtophyll morphotype Genus Myrtoidea Passalia, Romero and Panza, 2001 Type species. Myrtoidea patagonica Passalia, Romero and Panza, 2001 Myrtoidea sp. Fig. 4 Studied material. MPEF-Pb-Mz 6641, 6646e6648, 6654e6655, 6659, 6662, 6664, 6672, 6674e6676, 6678, 6680, 6684, 6687, 6689, 6691e6694, 6696e6697, 6747, 6748; and perhaps 6662, 6677, 6683, 6688 (all specimens from DE2). Description. Simple, microphyllous leaves, with marginal petiole attachment. Laminar shape oblong, medial symmetry either symmetrical or asymmetrical in slightly falcate leaves. Leaf margin untoothed. Lamina dimensions comprise between 9e12 cm long and 1.2e2 cm wide (ratio L:W typically 6e8:1). The largest specimen (MPEF-Pb-Mz 6747; Fig. 4A and H) is at least 12 cm long and 2 cm wide. Leaf apex acute (between 30e45 ), straight in shape (Fig. 4B and I). Base acute (between 25e40 ) typically cuneate and decurrent. Petiole short, with no more than 0.5 cm long, flanked by a thin extension of laminar tissue. Primary venation pinnate. Midvein with stout to typically massive size. Major secondaries simple brochidodromous. Secondaries (3 per centimetre in average), mostly regular spaced, decurrently attached in uniform acute angles (30e45 ) and with relative thickness fine to hairlike. Venation of tertiary and higher order not preserved. Remarks. This is the more abundant morphotype of the DE2 locality with more than 25 specimens. The straightening of the exmedial brochidodromous secondary arc segment is observed in the specimen MPEF-Pb-Mz 6696 (Fig. 4M) and is here considered as an intramarginal vein. The specimen MPEF-Pb-Mz 6641 (Fig. 4DeE and KeL) develops a lateral vein admedially forked resulting in two branches of quite similar gauge (see white and black arrowheads in Fig. 4E and L respectively). They may be interpreted as two secondary veins, or possibly one of them a secondary and the other an intersecondary. The presence of such fine secondary veins suggests the development of tertiary and higher order veins at least as thin as secondaries. This fact, coupled with the possibility that the leaves possess a thick mesophyll, could explain why the higher order veins are indistinguishable. In fact, the thin secondary venation has been partially preserved in only a few leaves. Despite the larger number of specimens, the terminal apex is not fully preserved in any leaf. Comparisons. Leaves with elongate (lorate) laminas with entire margins, venation pinnate, brochidodromous, with numerous secondaries forming a distinctive intramarginal vein, are the features that define the myrtophyll morphotype in the sense of Hickey (1984) and Zastawniak (1994). Leaves of myrtophyll physiognomy are known, at least, from the AlbianeCenomanian in both hemispheres (i.e. Berry, 1937; Kva cek, 1983; Hickey, 1984; Passalia et al.,

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2001; Iglesias et al., 2007; Coiffard et al., 2009). Many fossil and extant generic names have been applied to myrtophyll fossil leaves. Some of them are used for impressions (i.e. Myrciophyllum Engelhardt 1891; Myrtoidea Passalia et al., 2001) while others are applied to fossil leaves with both architectural and cuticular features (i.e. Eucalyptophyllum Fontaine 1889 with cuticular characters added by Upchurch, 1984; at least partially the Myrtophyllum group sensu Kvacek, 1983; Myrtaciphyllum Christophel and Lys, 1986; Eucalyptolaurus Coiffard et al., 2009). The specimens of Puesto Manuel Arce resemble myrtophyll leaves previously described from the Cretaceous of Patagonia as Myrtoidea patagonica Passalia et al. (2001) from the Bajo de los Corrales (?AlbianeCenomanian), Myrcia santacruzensis Berry (1937) from Mata Amarilla Formation (CenomanianeConiacian) and Myrcia angustifolia Hüniken (1995) from the Cerro Cazador Formation (CampanianeMaastrichtian). These species consist of elongated leaves, typically oblong (or elliptic) including slightly falcate forms, with a ratio L:W up to 4e5:1 (until 10:1 in Myrcia angustifolia), base and apex acute, petiole short, flanked by a thin and decurrent laminar tissue, margin entire, venation pinnate brochidoromous conformed by a midvein stout or massive, secondaries with relative thickness fine to hairlike and a distinctive intramarginal vein. The genus Myrtoidea includes leaves with numerous unbranched secondary veins as well as admedially or exmedially ramified and commonly branched intersecondaries. As mentioned above, the specimen MPEF-Pb-Mz 6641 (Fig. 4DeE and 4KeL) develops a lateral vein that may be interpreted as an intersecondary as well as a branch of a secondary vein admedially ramified. Both interpretations consist of features that are consistent with Myrtoidea. The species Myrtoidea patagonica is characterized by the usual presence of a second intramarginal vein (Passalia et al., 2001). According to the terminology of Ellis et al. (2009), this double intramarginal vein connected by transversal veinlets, consists of two perimarginal veins with quite similar gauges: an intramarginal secondary and, exmedially, a fimbrial or marginal secondary vein. As mentioned above, in one specimen of Puesto Manuel Arce (MPEF-Pb-Mz 6696; Fig. 4M) the straightening of the exmedial brochidodromous secondary arc segments results in an intramarginal vein. However, this specimen differs from Myrtoidea patagonica in that there is no evidence of the development of a second perimarginal vein. The presence of one or two intramarginal veins formed by secondary or tertiary arcs has been mentioned by Iglesias et al. (2007) in the description of small leaves from the Mata Amarilla Formation, grouped in the MA103 morphotype. Iglesias et al. (2007) point out that the MA103 leaves share, with Myrtoidea patagonica, the presence of numerous thin secondaries; however can be distinguished of this species by having ovate laminar shape and rounded or retuse apex. Iglesias et al. (2007) also described a set of elongated leaves with development of the intramarginal veins which were categorised in the MA104 and MA105 morphotypes. Another species comparable in gross morphology and venation is Myrcia santacruzensis Berry, and although they are of a similar length, the leaves of Puesto Manuel Arce have a slightly higher L:W ratio. This species was also recognized from the Maastrichtian (Zamek Formation) of Antarctica by Zastawniak (1994) who changed the generic name and described the new form now as Myrciophyllum santacruzensis (Berry) Zastawniak.

the notably difference in gauge among the mid-vein (white arrowheads) and a secondary vein (white arrows) (MPEF-Pb-Mz 6696). HeP. line drawing of leaves figured in AeG. H. (see also Fig. 4A) (MPEF-Pb-Mz 6747). I. (see also Fig. 4B) (MPEF-Pb-Mz 6675). J. (see also Fig. 4C) (MPEF-Pb-Mz 6672). KeL. (see also Fig. 4D, E) (MPEF-Pb-Mz 6641). L. Detail of Fig. K (see explaining above for black arrows and arrowheads). M. Note the straightening of the exmedial brochidodromous secondary arc segment resembling an intramarginal vein (MPEF-Pb-Mz 6696). N. (MPEF-Pb-Mz 6647). O. Leaf base (see also Fig. 4F) (MPEF-Pb-Mz 6694). P. (MPEF-Pb-Mz 6693). Scales AeD, HeK, MeP ¼ 1 cm, F ¼ 0.5 cm, E, G, L ¼ 0.2 cm.

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The leaves of Myrtoidea sp. from Puesto Manuel Arce share a high L:W ratio with Myrcia angustifolia Hünicken as well as the presence of specimens with falcate lamina, but the latter species has a distinctive high number of secondary veins. Botanical affinity. Leaves of the myrtophyll morphotype are characterized by the development of brochidodromous secondaries arcs that define a more or less distinctive intramarginal vein. This architectural feature was recognized in a number of extant plant groups and added to other leaf characters, resulted in Hickey and Wolfe (1975) creating a so called “Ochnaceous Alliance” (in part, consisting of Myrtales, Primulales, Clusiaceae, Dioncophyllaceae, Dipterocarpaceae, Sapotaceae). The orders and families included in the “Ochnaceous Alliance” were considered part of a Dilleniidae subset that those authors called “pinnate Dilleniidae”. According to the APG III (2009) system, the major part of the“pinnate Dilleniidae” plant groups is placed mostly in the Rosids and Asterids. Among the Myrtaceae (Myrtales), intramarginal veined leaves, with linear to lanceolate, symmetrical to falcate shape, are common in the Tribe Eucalypteae (see Hermsen et al., 2012 and cites therein). Intramarginal veins are also present in Gentianales and Ericales (“Dillenid-leafed Asterids” of Hickey and Wolfe, 1975; Asterids in APG III, 2009). The development of pinnate veined leaves with an intramarginal could have had multiple origins, being either an ancestral or derivate condition depending on the extant plant group considered (see discussion in Doyle, 2007). In the fossil record, leaf impressions with “Myrtophyll” architectural traits have been commonly assigned to the Myrtaceae (i.e. Myrcia santacruzensis Berry, 1937). In some cases, the preservation of cuticle details (i.e. Myrtaciphyllum Christophel and Lys, 1986) or associated infructescences/capsules support the myrtaceous (i.e. Eucalyptus spp., Gandolfo et al., 2011) or at least myrtalean (Syzygioides americana (Lesquereux) Manchester et al., 1998) affinity. However, as in the extant plant, this venation pattern appears in fossil leaves with other botanical affinities, as for example in the lauraceous Eucalyptolaurus depreii Coiffard et al. (2009) or in the unresolved (Chloranthaceae?, Illiciales?) Eucalyptophyllum oblongifolium Font. (Upchurch, 1984). 4.1.2. Palmatilobed palinactinodromous morphotype Bamfordphyllum gen. nov. Type species. Bamfordphyllum crassivena sp. nov. Diagnosis. Simple, microphyllous to nothophyllous leaves, with a petiole of marginal position. Laminar shape approximately elliptic, symmetrical to quite asymmetrical. Leaf blade palmately lobed, with typically 3 main lobes, each one formed by 2e3 minor lobes. Leaf margin untoothed. The lobes are convex in shape and end in a mucro. Base acute to obtuse, shape concave to concave-convex. Primary venation palinactinodromous, typically with three main veins of stout size arising decurrently from the petiole. The mid primary vein reaches the apex of the leaf. Lateral primaries dichotomize 2e3 times originating “subprimaries”. Some “subprimaries” reach the apex of lobes, while others are directed toward the sinus dichotomizing near the leaf margin and outlining an intramarginal vein that runs through the distal or proximal sides of lobes. Lobes are typically vascularized by three main veins; a principal mid-vein and two accessory (intramarginal) veins that fuse in the terminal lobe apex. A weak vein disposed closely parallel to the leaf margin and exmedially to the intramarginal veins may be present in the lobes. Typically, one pair of secondaries originate from the mid-vein and curve upward until their course becomes subparallel or diverges slightly from the primary vein. These secondaries bifurcate and vascularize the apical lobes. Primaries, “subprimaries” and secondary veins stout to moderate with little differentiation in gauge. Venation of higher order not clearly preserved.

Bamfordphyllum crassivena sp. nov. Figs. 5 and 6 Holotype. MPEF-Pb-Mz 6720 (Figs. 5D and 6A) Sintypes. MPEF-Pb-Mz 6707 (Figs. 5A, 6G), 6728 (Figs. 5F and 6H). Diagnosis. As for genus. Derivation of name. The generic name “Bamfordphyllum” honours the paleobotanist Marion Kathleen Bamford who first described a Cretaceous leaf with these features. The species epithet “crassivena” derive from the Latin words “crassus” (¼thick) and “vena” (¼vein), in allusion to the characteristic vein thickness of these leaves. Type locality. Estancia Don Eduardo 1 (DE1), north side of Sierra Cuadrada, Chubut Province, Argentina. Stratigraphic horizon. Puesto Manuel Arce Formation, Chubut Group. Studied material. MPEF-Pb-Mz 6707, 6709e6710, 6712, 6714e6715, 6717e6718, 6720, 6727e6728, 6732e6733, 6737e6743 (all specimens from DE1). Description. Simple, microphyllous to nothophyllous leaves (Figs. 5 and 6), with a long petiole (Figs. 5J and 6F) of marginal position. Laminar shape approximately elliptic with medial symmetry to quite asymmetrical, and basal symmetry. The size of the lamina is approximately 3e7 cm long and 3e6 cm wide (ratio L:W around 1e1,4:1). Leaf blade palmately lobed, typically with 3 main lobes, each one formed by 2e3 minor lobes. The leaf margin is untoothed. Central lobe distally divided in 3 lobes; the mid-one representing the terminal apex of leaf, and two lateral lobes symmetrically arranged on each side (Figs. 5CeD, F and 6A, H). Lateral main lobes formed by 2 (Figs. 5F, I and 6C, H) or 3 minor lobes (Figs. 5A and 6G). The lobes are convex in shape and end in a mucro (white arrow in Fig. 5C). Base acute (Figs. 5D and 6A) to obtuse (Figs. 5A and 6G) of shape concave (Figs. 5D and 6A) to concave-convex (Figs. 5A and 6G). The primary venation is of palinactinodromous type. In general three main veins of moderate to stout size arise decurrently from the petiole. The mid-vein reaches the apex of leaf. Typically, one pair of lateral veins (“secondaries”, white arrowheads in Fig. 6A, G), opposite to subopposite, originate from the mid-vein at acute angles and curve upward until their course becomes sub-parallel or diverge slightly from the primary vein. This veins run throughout the central lobe toward the little lateral lobes developed in the apex of the leaf. Lateral primaries dichotomize 2e3 times originating “subprimaries” (black arrowheads in Fig. 6A, G). Some “subprimaries” reach the apex of lobes, while others are directed toward the sinus dichotomizing near the leaf margin and outlining an intramarginal vein (white arrows in Figs. 5C and 6C, G) that run through the distal or proximal sides of lobes. Consequently the lobes are typically vascularized by three main veins; a principal mid-vein and two accessory (intramarginal) veins that fuse in the terminal lobe apex. In some leaves, an ultimate branching of “subprimaries” can be distinguished almost on the sinus of the lobes. This branching originates weak veins disposed closely parallel to the leaf margin and exmedially to the intramarginal veins (black arrows in Fig. 6C, G). Venation of higher order not clearly preserved. Remarks. This is the more abundant morphotype of the DE1 locality with at least 19 specimens studied. Recognizing hierarchical vein orders is difficult in this morphotype. The main vein network consists of a fan-shaped vein pattern that is a product of successive dichotomic divisions of primaries from a palinactinodromous model. Typically the veins are disposed with a relatively straight course or are smoothly curved. Another feature is

Fig. 5. Palmately lobed palinactinodromous dicot leaves from the Puesto Manuel Arce Formation. AeJ. Bamfordphyllum crassivena gen. et sp. nov. A. General view of a specimen with base obtuse (see also Fig. 6G) (MPEF-Pb-Mz 6707). B. Fragment of central and lateral lobe (see also Fig. 6E) (MPEF-Pb-Mz 6732). C. Detail of a central lobe composed by a mid-lobe flanked by two lateral lobes; white arrowhead indicates an obscure deposit corresponding to the terminal mucro; white arrows indicate two intramarginal veins (accessories) (MPEF-Pb-Mz 6727). D. General view of a specimen with base acute (see also Fig. 6A) (MPEF-Pb-Mz 6720). E. (see also Fig. 6D) (MPEF-Pb-Mz 6712). F. (see also Fig. 6H) (MPEF-Pb-Mz 6728). G. (see also Fig. 6B) (MPEF-Pb-Mz 6738). H. (MPEF-Pb-Mz 6737). I. (see also Fig. 6C) (MPEF-Pb-Mz 6715). J. Leaf with petiole preserved; white arrowheads indicate the distal and proximal extremes of the petiole (see also Fig. 6F) (MPEF-Pb-Mz 6712). Scales A, D, F and I ¼ 1 cm; BeC, E, GeH, J ¼ 0.5 cm.

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Fig. 6. Line drawing of selected specimens of Bamfordphyllum crassivena gen. et sp. nov. White arrowheads indicate secondary veins originated from the mid-vein that runs throughout the central lobe. Black arrowheads indicate “subprimaries” originated from lateral primary veins. White arrows indicate intramarginal veins originated from “subprimaries”. Black arrows indicate weak veins disposed closely parallel to the leaf margin and exmedially to the intramarginal vein. A. (see also Fig. 5D) (MPEF-Pb-Mz 6720). B. (see also Fig. 5G) (MPEF-Pb-Mz 6738). C. (see also Fig. 5I) (MPEF-Pb-Mz 6715). D. (see also Fig. 5E) (MPEF-Pb-Mz 6712). E. (see also Fig. 5B) (MPEF-Pb-Mz 6732). F. (see also Fig. 5J) (MPEF-Pb-Mz 6712). G. (see also Fig. 5A) (MPEF-Pb-Mz 6707). H. (see also Fig. 5F) (MPEF-Pb-Mz 6728). I. (MPEF-Pb-Mz 6712). Scale ¼ 1 cm.

that the development of the venation network is quite symmetrical at each side of the mid-vein. The venation found immediately below the sinus separating two leaf lobes (sinal brace), may be classified as types 1 to 3 in the sense of Hermsen (2005); this is weak veins (from different origin) bifurcating below the sinus. The petiole is presumably long (at least, 2 cm long), considering it is preserved only in a (young?) very small leaf (Figs. 5J and 6F). Comparisons. Palmatilobed palinactinodromous leaves are known, at least, from the mid-Cretaceous in both hemispheres. Different fossil and extant genera have been used to denominate leaves with these features, some of which were grouped by Crabtree (1987) in the Pentalobaphyll (Araliaephyll) and Platanophyll morphotypes. Among the southern hemisphere records, the Puesto Manuel Arce specimens resemble the “Robustavena lobata” Bamford (1989) from the Turonian deposits of Orapa Pipe (Botswana). This is especially true with the specimen MPEF-Pb-Mz 6707 (Figs. 5A and 6G). “Robustavena lobata” is based on a single leaf that lacks basal and apical ends. Despite this the shape of the lobes and their major vein network, including the thickness of veins of “Robustavena lobata” has an identical development to that observed in the leaves of Puesto Manuel Arce. The density of main veins is also identical. As in the Patagonian specimens, in “Robustavena lobata” the veins of higher order are not preserved. Bamford (1989) mentioned that “Robustavena” presents palinactinodromous venation. However, due to the absence of the leaf base and of the origin of primary veins, this character, although probable, can not be determined. Due to their resemblance, specimens from both localities (Patagonia and Orapa Pipe) could possibly be found to be conspecific. The proposal of the new name Bamfordphyllum crassivena for the Patagonian specimens is because “Robustavena lobata” is considered a name not validly published according to the ICBN (McNeill et al., 2012). There are fossil leaves from the Cretaceous of Patagonia that also resemble Bamfordphyllum crassivena. This is the case of the

MA106 morphotype from the CenomanianeConiacian Mata Amarilla Formation, Argentina (Iglesias et al., 2007). Similarities are especially distinguishable with the specimens MPM-PB1392 and 1412 of Iglesias et al. (2007 figs. 7.D and 7.G) with which Bamfordphyllum crassivena shares the shape of the lobes. The venation pattern of primaries, “subprimaries” and secondaries is basically identical, although the density of main veins is apparently higher in the Puesto Manuel Arce specimens. Unfortunately, higher order veins are not preserved in the Puesto Manuel Arce specimens, precluding a comparison at this level. The Mata Amarilla specimens grouped in the MA106 morphotype include leaves with lobes quite variable in shape and number. In this sense, the specimens of Puesto Manuel Arce have lamina with a more homogeneous development. The species Sterculia washburnii Berry (1928) from Mata Amarilla, includes a variety of leaves 3e5 palmately lobed and actinodromous or palinactinodromous venation. A fragmentary leaf enclosed in this species (Berry, 1928 pl.4 fig.5) is comparable to the apical portion of some specimens of Puesto Manuel Arce. Summarizing, the specimens of Puesto Manuel Arce appear to be more similar to the southern African specimens of “Robustavena lobata” rather than to those of Mata Amarilla. Nevertheless, following the criteria of Iglesias et al. (2007) for the parataxon MA106, all these leaves (“Robustavena lobata” together with those from Puesto Manuel Arce and Mata Amarilla) may be grouped in a single morphotype that includes a continuous series of forms. It is even possible that some of these leaves have been part of the same natural group. Other possibly comparable leaves come from the Portezuelo Formation (upper Turonianelower Coniacian), Argentina and have been grouped as “morfotipo A” (Passalia et al., 2008). They consist of fragmentary leaves and are part of a small assemblage. The disposition of the main veins is similar to those of the Manuel Arce leaves, but they differ in that their lamina is less incised and consequently they are treated as toothed rather than lobed.

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Botanical affinity. Palmatilobed leaves with palinactinodromous venation of similar development occur in extant Grossulariaceae from the section Symphocalyx Berland. as Ribes odoratum Wendl. and the closely related species Ribes aureum Pursh. The section Symplocalyx includes species with leaves having distinctive features that distinguish them from other Ribes species. Among them, Hermsen (2005) point out the type of margin (lobed rather than toothed) and the presence of a few secondary veins, with a characteristic disposition, as the more important characters. To this respect this author states that “in many cases, the first pair of secondary veins arises at an acute angle in the proximal half of each leaf lobe and curves markedly upward, paralleling the course of the primary vein from which their arise, either on straight or slightly diverging course”. This same course of secondary veins can be observed in Bamfordphyllum crassivena (see white arrowheads in Fig. 6A, G). Summarizing, the Symphocaylx-type leaf as characterized by Hermsen (2005) includes features recognized in the fossilized leaves of Puesto Manuel Arce. The species encompassed in the section Symplocalyx occur in the north-western and central United States to northern Mexico. The genus Ribes is very broadly distributed around the Northern Hemisphere, and extends south in the mountains of South America reaching the Patagonian template forests of southern Argentina and Chile, but is especially diverse in western North America, both in terms of the number of species and the representation of major subclades (Schultheis and Donoghue, 2004). In spite the resemblance between Bamfordphyllum crassivena and the species of the section Symphocalyx, the extant distribution of Ribes suggests dispersal from North America to South America which is in conflict with the possibility of a midCretaceous evidence from Patagonia. For the time being, there are no sure evidences of Grossulariaceae during the Cretaceous, and their Cenozoic record consists mainly of leaf fossils from North America where Ribes extends back to the Eocene (Hermsen, 2005; Friis et al., 2011). In the southern Hemisphere, a probably Grossulariaceae affinity was suggested for a flower from the middle
rctica (Gandolfo et al., 1998). Eocene of Anta The widely distributed Ranunculaceae also exhibit extant species having leaves with more or less dissected lamina than those of Puesto Manuel Arce (and possibly a more complex venation), but with similar appearance (i.e. Ranunculus peduncularis Sm., R. platensis A. Spreng., R. repens L.). 4.1.3. Palmately lobed actinodromous morphotypes Two morphotypes fit with these features (palmately lobed lamina and actinodromous primary vein) but differ mainly in their major secondary vein framework and type of margin. 4.1.3.1. Palmatilobed craspedodromous morphotype. Genus. Dicotylophyllum auct. non. (used in the sense of Halamski, 2013). Dicotylophyllum sp.1

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consisting of three primary veins of moderate size and straight course that reach the apex of lobes. Central lobe vascularized by the mid-vein and 3e4 pairs of major secondaries (black arrows in Fig. 7E) of craspedodromous type. Secondary veins spacing decreases distally, with uniform, narrow to moderate emerging angle, quite straight course and relative thickness moderate. Lateral lobes vascularized by lateral primaries, agrophic veins (minor secondaries, white arrowheads in Fig. 7EeF) of craspedodromous type and interior secondaries (black arrowhead in Fig. 7E). Near the margin, minor secondaries produce proximal and distal branches of secondary or tertiary gauge which reach the leaf margin. Intercostal tertiary veins of mixed percurrent type; disposed at obtuse angle with respect to the midvein and apparently tending to be concentric to the base of the lamina. Quaternary and possible higher order veins form a net alternate percurrent to reticular type. Teeth (crenate) apparently belong to a single order, with sinus angular and shape convexeconvex. Teeth vascularized by a principal vein that terminates at the rounded tooth apex; at seems, there are no accessory veins. Remarks. This morphotype is established on the basis of six fragmentary leaves. Nevertheless the venation pattern and the features of the margin are exactly the same in all cases allowing them to be considered as a single morphotype. Two specimens are the most complete (MPEF-Pb-Mz 6700 and 6658, Fig. 7A, B and 7E, H) and consequently the general shape of laminae, size and the length/width ratio were based on these specimens. The specimen MPEF-Pb-Mz 6658 (Fig. 7B, H) consists of a 3-lobed leaf. The blade of their lateral lobes apparently overlapped on the laminae of the central lobe (see white arrows on the sinus formed among lobes in Fig. 7H) a feature also suggested by specimen MPEF-Pb-Mz 6644 (Fig. 7C, F). This feature possibly implies that the laminae had some degree of undulation with their foliar tissue developed in more than one plane. The specimen MPEF-Pb-Mz 6700 (Fig. 7A, E) preserves only one lateral lobe, however the symmetry of their venation presumes that their lamina also consisted of three lobes. The specimen MPEF-Pb-Mz 6644 (Fig. 7C, F) although fragmentary is the longest. Using the length/width ratio of 1:1, and a distance of 5 cm from the mid-vein to the margin of lateral lobe, it is possible to estimate that this specimen consists of a mesophyll leaf around 10 cm long. Because of the depth of some incisions of the laminae in lateral lobes (especially in the proximal side) the projections formed could be considered as lobes rather than teeth. In consequence the lateral lobes could be described as pinnately lobed instead of crenate (toothed). Although the petioles are not preserved, their attachment would be determined as marginal. The teeth shape and their vascularization (by a medial principal vein) fit with the “Malvoid” type sensu Hickey and Wolfe (1975). However, Carvalho et al. (2011) point out that the “Malvoid” tooth generally have accessory veins forming a series of looping arches that terminate at the tooth apex; a feature not observed in Dicotylophyllum sp.1.

Fig. 7 Studied material. MPEF-Pb-Mz 6644, 6652, 6658, 6663, 6698e6700 (all specimens from DE2). Description. Simple, microphyllous to nothophyllous leaves, with marginal petiole attachment. Laminar shape elliptic with medial symmetry at least 5 cm long and 6 cm wide (ratio L:W around 1,1e0,8:1). Leaf blade palmately lobed, typically with 3 main lobes and margin crenate. Terminal lobe with apex not completely preserved; lateral lobes with apex acute, convex to rounded in shape. Base partially preserved, with angle reflex and shape cordate. Primary venation of basal actinodromous type;

Comparisons.The genus name Dicotylophyllum auct. is used here in the sense of Halamski (2013). There are not fully comparable foliar records in the Cretaceous of Patagonia. Possibly, a species that is relatively similar is Thorhallenia dentata Passalia (2007) from the upper Albian e lower Cenomanian Kachaike Formation. It consists of toothed, craspedodromous leaves that include forms with incised lamina, giving the appearance of being lobed. Furthermore, it has opposites or subopposite secondaries, agrophic veins and a similar arrangement of tertiary veins. However, T. dentata develops teeth of more than one order, some of which are vascularized by a middle main vein and one or two lateral accessories, features not observed in Dicotylophyllum sp.1. Dicotylophyllum resembles

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Fig. 7. Palmately lobed craspdodromous dicot leaves from the Puesto Manuel Arce Formation. AeH. Dicotylophyllum sp.1. A. (see also Fig. 7E) (MPEF-Pb-Mz 6700). B. (see also Fig. 7H) (MPEF-Pb-Mz 6658).C. (see also Fig. 7F) (MPEF-Pb-Mz 6644). D. (see also Fig. 7G) (MPEF-Pb-Mz 6652). EeH. Line drawing of the specimens figured in AeD. Black arrows indicate major secondaries, white arrowheads indicate agrophic veins (minor secondaries), black arrowhead indicates an interior secondary vein and white arrows indicate sinus apparently overlapped. E. (see also Fig. 7A) (MPEF-Pb-Mz 6700). F. (see also Fig. 7C) (MPEF-Pb-Mz 6644). G. (see also Fig. 7D) (MPEF-Pb-Mz 6652). H. (see also Fig. 7B) (MPEF-Pb-Mz 6658). All scales ¼ 1 cm.

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indeterminate fragmentary leaves from the uppermost Cretaceous of New Zealand (leaf form PB13 in Kennedy et al., 2002, figs. 4.n and 7.d; and perhaps Pole, 1992, fig. 89). Some Cretaceous forms from the Northern Hemisphere, which may be grouped in the Platanophyll morphotype of Crabtree (1987), are only superficially comparable to Dicotylophyllum sp.1 (i.e. Platanus sp., Bell, 1956, pl. 81, fig. 6; Sertia kiensis Golovneva and Nosova, 2012, Aspidiophyllum denticulatum Wang and Dilcher, 2006). Leaves palmatilobed, toothed, with a cordate base, actinodromous primary venation and craspedodromous secondaries, referred to the extant genus Ribes L. (Grossulariaceae), have been described from Cretaceous and especially Tertiary deposits of North America. These fossil records, revised in detail by Hermsen (2005), include species (i.e. Ribes lacustroides Axelrod) that have some resemblance to Dicotylophyllum sp.1. Leaves with these features have been also recognized in the EoceneeOligocene of Patagonia
sari (i.e. as Rubus primaverae Frenguelli, 1941; and Saxifragaceae? Ce et al., 2006). Possibly the major difference between Dicotylophyllum sp.1 and these fossil Ribes-like records reside in the shape and venation (typically rosoid type in Ribes, Hermsen, 2005) of the teeth.
tegui encompasses palmatiThe genus Malvaciphyllum Anzo veined fossil leaves with affinities to extant Malvaceae. This genus includes records from the Miocene and Pliocene of Northern
tegui Argentina and Brasil (Malvaciphyllum quenquiadensis Anzo
tegui and Cristalli, 2000) and the and Malvaciphyllum sp. Anzo middleelate Paleocene of Colombia (Malvaciphyllum macondicus Carvalho et al., 2011). The diagnosis of Malvaciphyllum includes the
tegui development of four or more actinodromous primaries (Anzo and Cristalli, 2000) and Dicotylophyllum sp.1 consists only of three actinodromous pimary veins. For this reason this fossil genus is not adopted. In spite of them, Dicotylophyllum sp.1 has features shared with the species of Malvaciphyllum described. They are the lobed lamina (including cordate base); teeth of malvoid type with a single mid-vein (as M. quenquiadensis); secondary venation craspedodromous, with major secondaries decreasing in spacing distally and minor secondaries producing branches both proximally and distally close to the margin; and tertiaries percurrent tending to be concentric to the base of the lamina. Botanical affinity. Leaves similar to Dicotylophyllum sp.1, namely characterized by a cordate base, lobes more or less defined, margin with teeth or crenate, actinodromous primary venation and craspedodromous secondaries, are recognized in extant genera belonging to Rosidae as i.e. Corynabutilon (K.Schum.) Kearney (Malvaceae) or Physocarpus (Cambess.) Raf. (Rosaceae) as well as other eudicots such as Ribes L. (Grossulariaceae). Palmativeined leaves with malvoid tooth-type, are characteristics of Malvaceae (Hickey and Wolfe, 1975; Carvalho et al., 2011). 4.1.3.2. Palmatilobed brochidodromous morphotype (“Magnoliaephyll” morphotype). Genus. Araliaephyllum Fontaine 1889 Type species. Araliaephyllum obtusilobum Fontaine, 1889 Araliaephyllum sp. Figs. 8AeC and 9A Studied material. MPEF-Pb-Mz 6706, 6721, 6713 and 6734 (all specimens from DE1). Description. Simple, mesophyllous leaf, with marginal petiole attachment. Laminar shape elliptic with medial symmetry at least

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8 cm long and 9.5 cm wide (ratio L:W 0,8:1). Leaf blade palmately lobed, with 3 lobes (to 5 lobes if MPEF-Pb-Mz 6713, Fig. 8B is included, see comment below) and margin untoothed. Length of lobes reaches slightly more than 2/3 leaf length. Central lobe with apex acute, convex in shape. Base symmetrical with angle obtuse (near to 180 ) and shape rounded. Primary venation of basal actinodromous type (to palinactinodromous if MPEF-Pb-Mz 6713, Fig. 8B is included, see comment below); consisting of three primary veins of stout size and straight course that reach the apex of lobes. The primary veins terminate in an apparently retuse apex. Major secondaries (see black arrowheads in Fig. 8C) are simple brochidodromous. Secondaries (7e9 pairs) indistinctly opposite or alternate, spacing irregularly, with emerging angle narrow to moderate (around 45 ) mostly uniform and attachment decurrent. Secondaries with relative thickness fine to hair-like and course somewhat irregular. Secondary veins join to form arches whose shape gradually varies from quite plane to convex. In this latest case, exmedial loops are developed between contiguous secondary arches. Intercostal areas with irregular shape and size. Interior secondaries (see black arrows in Figs. 8C and 9A) and intersecondaries (see white arrowheads in Figs. 8C and 9A) are present. Intramarginal secondary observed only in the leaf base (basilaminar vein?). No reinforced sinus bracing veins are recognized. Venation of tertiary and higher order not clearly preserved. Remarks. This morphotype has been described on the basis of the more complete and best preserved specimen (MPEF-Pb-Mz 6721, Fig. 8A, C and 9A) who consists of an imprint and its counterpart. However, three other fragmentary leaves were also placed in this taxon. Specimens MPEF-Pb-Mz 6706 and 6734 (both not illustrated) consisting of microphyll, actinodromous leaves with three primaries stout, secondaries very thin, margin palmately lobed (3-lobed in MPEF-Pb-Mz 6706), untoothed. Their base angle and shape also justifies their inclusion. The specimen MPEF-Pb-Mz 6713 (Fig. 8B) also shares these features but has a lobate base shape by the development of two subordinate lateral lobes, and a palinactinodromous primary venation. For this reason, this specimen is included with doubt and with further material may be shown to belong to another taxon. Comparisons. Araliaephyllum Fontaine (1889) was proposed to describe a number of 5-lobed Cretaceous leaves with palinactinodromous primary venation from the Northern Hemisphere Potomac Group. Here this taxon is used in the broad sense adopted in previous works including 3e5-lobed, untoothed, actino/palinactinodromous leaves (i.e. Bell, 1963; Krassilov, 1973; Cantrill and Nichols, 1996; Golovneva and Nosova, 2012). These features, together with the brochidodromous or festooned brochidodromous secondaries characterize a set of northern Laurasian taxa that Crabtree (1987) placed in the “Magnoliaephyll morphotype”. Araliaephyllum sp. and other taxa (i.e. Sterculia spp.; Araliaephyllum cachetamanense) previously recorded from the mid-Cretaceous of
ndez, 1959; Hüniken, 1995; Patagonia (i.e. Berry, 1928, 1937; Mene Archangelsky et al., 2009) may be included in the “Magnoliaephyll morphotype”. Among them, the species most similar to Araliaephyllum sp. is Sterculia sehuensis Berry (1937) from the CenomanianeConiacian Mata Amarilla Formation. The specimens from both sources are similar in the shape of the lamina, with an obtuse base, rounded to convex; the development of divergent lobes, with rounded sinuses and the venation pattern. Intramarginal secondary veins developed in the leaf base of the Puesto Manuel Arce specimen is apparently recognized also in S. sehuensis. However, some differences can also be highlighted. The sinuses which separate the lobes in Araliaephyllum sp. are generated by a relatively deeper incision of the lamina. This constriction in the base of the middle lobe results in strongly convex margins, rather

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Fig. 8. Palmately lobed brochidodromous and palmately compound dicot leaves from the Puesto Manuel Arce Formation. AeC. Araliaephyllum sp. A. General view of the main 3lobed leaf (see also Fig. 9A) (MPEF-Pb-Mz 6721). B. specimen 5-lobed assigned to Araliaephyllum sp. but with doubt. White arrowhead indicates the point of bifurcation of the palinactinodromous primaries (MPEF-Pb-Mz 6713). C. Detail of Fig. A which highlights some major secondary veins (black arrowheads), interior secondaries (black arrows, see also Fig. 9A) and intersecondaries (white arrowheads, see also Fig. 9A). DeG. cf. Sapindopsis sp. DeE. (see also Fig. 9H) (MPEF-Pb-Mz 6723). E. Detail of Fig. D showing the teeth margin. F. (see also Fig. 9I) (MPEF-Pb-Mz 6730). G. (see also Fig. 9G) (MPEF-Pb-Mz 6722). Scales AeD, FeG ¼ 1 cm, E ¼ 0.5 cm.

than the lightly convex to nearly straight margins of the middle lobe of S. sehuensis. The brochidodromous secondary arches of Araliaephyllum sp. gradually vary from quite plane to convex, producing some exmedial loops. Their development in S. sehuensis is

similar although the exmedial loops, as well as the presence of intersecondaries, are not illustrated or mentioned by Berry and neither is easily recognized in the type specimens. Iglesias et al. (2007) includes the Sterculia sehuensis Berry's specimens from

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Fig. 9. Line drawing of selected dicot leaves from the Puesto Manuel Arce Formation. A. Araliaephyllum sp. General view of the main 3-lobed leaf reconstructed from the imprint and the counterpart of specimen MPEF-Pb-Mz 6721 (see also Fig. 8A, C). Black arrows indicate interior secondaries (see also Fig. 8C) and white arrowheads indicate intersecondary veins (see also Fig. 8C). B. Dicotylophyllum sp.2 (see also Fig. 10AeB) (MPEF-Pb-Mz 6719). Black arrowheads indicate a secondary vein admedially forked. C. Dicotylophyllum sp. 4 (see also Fig. 10DeE) (MPEF-Pb-Mz 6722). D. Dicotylophyllum sp. 5 (see also Fig. 10F) (MPEF-Pb-Mz 6744). E. Dicotylophyllum sp. 3 (see also Fig. 10C) (MPEF-Pb-Mz 6679). FeI. cf. Sapindopsis sp. F. (MPEF-Pb-Mz 6735). G. Petiole length in this leaf has been drawn based in the countepart (see also Fig. 8G) (MPEF-Pb-Mz 6722). H. (see also Fig. 8DeE) (MPEF-Pb-Mz 6723). I. (see also Fig. 8F) (MPEF-Pb-Mz 6730). Scales AeB, E, FeI ¼ 1 cm; CeD ¼ 0.5 cm.

Mata Amarilla as part of the morphotype MA106. However, although belong to the same Formation, there are important differences in the development of the primary veins of MA106 and S. sehuensis specimens. The species Sterculia washburnii Berry (1928) from Mata Amarilla includes one specimen (op.cit., pl.4 fig. 1) with venation poorly preserved, but its lamina shape partially resembles that of Araliaephyllum sp. Berry (1937) stated that leaves identified by Kurtz as Sassafras acutilobum Lesquereux (now sinonimized in Sterculia kurtzii Hüniken, 1995) from the Patagonian Cerro Cazador Formation (CampanianeMaastrichtian) must correspond to Sterculia sehuensis. However, as noted by Hüniken (1995), the lobes of Sterculia kurtzii are longer and narrower, and its venation is actinodromous suprabasal and not basal as in Sterculia sehuensis. These differences also distinguish Sterculia kurtzii from Araliaephyllum sp. Leaves 3-lobed have been also recognized in the middle Albianelower Cenomanian Castillo Formation (Araliaephyllum
ndez, 1959 and morphotype 16mf of cachetamanense Mene Archangelsky et al., 2009). These share the development of a central lobe that is slightly narrowed at the base, with a convex to round apex, and secondaries veins forming more and less irregularly

brochidodromous arches with Araliaephyllum cachetamanense, but differ in the thickness of the primary veins. The shapes of the blade of morphotype 16mf are more similar to Sterculia kurtzii than to that of Puesto Manuel Arce and have brochidodromous arches distinctively more planes (pers. obs.). Palmativeined leaves are also known from the upper Albian (Araliaephyllum quinquelobatus Cantrill, in Cantrill and Nichols, 1996) and Maastrichtian of Antarctica (Sterculiaephyllum australis Dutra and Batten, 2000). Araliaephyllum quinquelobatus is a 3e5lobed leaf with lobes quite similar in shape to those of Araliaephyllum sp. of Puesto Manuel Arce, but with lobe sinuses less deep and secondaries and tertiaries forming a distinctive irregular mesh. Sterculiaephyllum australis lacks of the leaf margin which makes difficult a comparative analysis; but some veins details preserved show a pattern different to that of Araliaephyllum sp. Pole (1992) described mesophyll, 3-lobed leaves (parataxon MATA-3), with untoothed margin from the Matakaea Group, Upper Cretaceous of New Zealand. The author remarked that these leaves are similar to the Northern Hemisphere Potomac “platanoid” sequence (Hickey and Doyle, 1977). Parataxon MATA-3 consists of two incomplete specimens and only drawings of them were provided. In spite of that, there are some differences with the Puesto Manuel

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Arce specimens (depth and vascularization of sinus lobes, course of secondaries and apparently the relative thickness between primaries and secondaries). Palmatilobed leaves with actino/palinactinodromous venation are widely represented in the Cretaceous floras of Northern Hemisphere (i.e. Bell, 1963; Krassilov, 1973; Hickey and Doyle, 1977; Crabtree, 1987; Upchurch and Dilcher, 1990; Bugdaeva et al., 2006; Golovneva and Nosova, 2012). These leaves may be included either in “Pentalobaphyll”, “Platanophyll” or “Magnoliaephyll” morphotypes of Crabtree (1987) and comprise some taxa that exhibit similarities with Araliaephyllum sp. Within the Cretaceous North American Potomac Group, Sassafras potomacensis Berry (in Hickey and Doyle, 1977) is possibly the form most similar to Araliaephyllum sp. Both species share the gross shape of lobes, the relative thickness between veins of primary and secondary order and secondaries forming somewhat irregular brochidodromous arches. However, the foliar base in Sassafras potomacensis has a decurrent extension of blade toward the petiole, producing an acute basal angle and a suprabasal origin of the lateral primaries. In turn, the secondary veins, especially those of the central lobe, are projected toward the apex. These features close Sassafras potomacensis Berry and parataxon MATA-3 of Pole (1992), and distinguish these leaves from Araliaephyllum sp. A number of 3-lobed Araliaephyllum species have been described from the mid-Cretaceous of North America (i.e. Bell, 1963) and Eurasia (i.e. Krassilov, 1973; Golovneva and Nosova, 2012). Among them, Araliaephyllum ketorum Golovneva and Nosova (2012) from the Simonovo Formation, (Cenomanian) of Western Siberia has a strong resemblance to Araliaephyllum sp. This species consists of trilobate, untoothed leaves; base widely cuneate; lobes with rounded apices; central lobe slightly narrowed in base; actinodromous basal venation, with lateral veins diverging at about a 45 angle, straight, thin and 4-6 brochidodromous secondaries. Except for the different thickness of the mid-vein, the remaining features are easily distinguishable in Araliaephyllum sp. Botanical affinity. Leaves 3-lobed, untoothed, with three primary veins and brochidodromous secondaries occur in extant Magnoliidae (i.e. Laurales), as well as in a variety of taxa that be part of the “palmate Dilleniidae” group of Hickey and Wolfe (1975) and placed in the Rosidae by APG III (2009) (i.e. Sterculiaceae, Passiflorales, Euphorbiaceae, Malvaceae). Palmativeined 3 or 5-lobed leaves are also common in Eudicots (see Doyle, 2007). 4.1.4. Palmately compound morphotype cf. Sapindopsis Fontaine emend. Dilcher and Basson (1990) Figs. 8DeG and 9FeI Studied material. MPEF-Pb-Mz 6651 and 6660 (from DE2), 6722e6725, 6729e6731 and 6735 (from DE1). Description. Palmately compound leaf typically trifoliate, (mostly) microphyll to notophyll in size, with marginal petiole as long as 2 cm. Leaflets typically sessile, with nanophyll to microphyll size and ovate to elliptic shape at 3e5 cm long and 0,7e1.3 cm wide (ratio L:W 3.7e4.5:1). Leaflet margin toothed (crenate and serrate). Teeth simple (2e4 per centimeter) and small, with apex rounded and slightly incised sinus with angular shape (see detail in Fig. 8E). Central leaflet with medial and basal width symmetrical, apex acute with shape straight and base acute with a cuneate shape. Lateral leaflets similar to the central one but with basal width quite symmetrical (Figs. 8D and 9H) or definitively asymmetrical (Figs. 8G and 9G). Leaflets with pinnate primary vein and secondaries apparently joined in arches, brochidodromous or very possibly semicraspedodromous. Mid-vein stout in size. Some secondaries seem to reach the leaflet margin. Secondary veins (7e8?

pairs) indistinctly opposite or alternate, spaced irregularly, with emerging angle variation inconsistent. Tertiary and higher order veins are indistinguishable. Remarks. These leaves are described here as palmately compound and typically trifoliate. Mostly leaves (i.e. Figs. 8D, G and 9H, G) fit with this description. However, in others, the laminar incision almost reaches the petiole but without resulting clearly in distinct leafletes. This is the case of the specimen MPEF-Pb-Mz (Fig. 9F) which develops a fourth lobe. In these cases the leaves should be described as simple, palmatisect (with deep sinus), and the leaflets considered as lobes. The relative size of leaflets is uniform or well the lateral ones are quite minor. Although the leaflets are typically sessile they may exhibit a short petiolule (see lateral leaflet in Figs. 8D and 9H). This is the only morphotype sheared by two localities. Comparisons and discussion. The oldest trifoliate leaves known from the Southern hemisphere belong to the upper Aptian of San Luis Basin, Argentina (LC-Microphyll trifoliate, Puebla, 2009). However, beyond sharing the same type of foliar organization, there are no other similarities between the specimens of La Cantera and Puesto Manuel Arce. There are no leaves comparable to the Manuel Arce trifoliate specimens in other south Gondwanic Cretaceous assemblages. However, this situation changes if Tertiary floras are considered. Trifoliate leaves are present from the Danian of Patagonia (i.e. Morfotipo SA043 Cupania sp., Iglesias, 2007) and at least from the Eocene of Antarctica (i.e. Fildesia pulchra Rohn et al., 1987). The genus Sapindopsis Fontaine emend. Dilcher and Basson (1990) was first described from the middle Albian of the Patapsco Formation, Potomac Group of United States (Fontaine, 1889). It is characterized by even to odd pinnatifid or pinnately compound leaves, terminal lobes or leaflets commonly more or less united at their base, distal leaflets with lamina decurrent to the leaf rachis. Leaflets may be both sessile or with a short petiolule, ellipticals to lanceolate-shaped, with stout midrib extending to the apex of each leaflet. Secondary veins diverge from the midrib at various angles and patterns (Dilcher and Basson, 1990). The type of margin was not mentioned in their original diagnoses but the record of Sapindopsis includes species having both untoothed (mostly) and toothed margins. Sapindopsis is characterized by a highly variable outline of the leaf blade and variously decurrent leaflets (Golovneva, 2007). Although mostly and typically pinnately organizated, trifoliate specimens have been also included in this genus (see Sapindopsis sp. A and B in Huang and Dilcher, 1994; Sapindopsis sp. and “Sapindopsis ternata” Miller and Hickey in Miller, 2007). Moreover, the trifoliate (ternate) leaf organization state was added by Miller (2007) to the diagnoses of Sapindopsis. The Manuel Arce Formation specimens fit with the gross characterization of Sapindopsis except for the number of leaflets, which is solved if it is considered that the trifoliate forms be included in this genus. It is not possible to compare higher order venation and epidermal details as these are unpreserved. The Sapindopsis foliage is a characteristic element in the late Albian assemblage from the Potomac Group (i.e. Hickey and Doyle, 1977; Upchurch et al., 1994) but also occurs in other AlbianeCenomanian floras from the Northern Hemisphere. Among them are those from the center of the United States (Berry, 1922; Huang and Dilcher, 1994), northern areas of North America (Bell, 1956), Greenland (Boyd, 1998) and several localities of Eurasia (i.e. Dilcher and Basson, 1990; Golovneva, 2007 and cites therein). The well documented record of Sapindopsis, especially from North America, suggests a sequence of successive changes in their leaf morphology through the mid-Cretaceous (i.e. Hickey and Doyle,

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1977). In contrast, the single mention of this genus in Cretaceous assemblages from the southern hemisphere is “Sapindopsis australis” Bamford (1989), a pinnatisect leaf belonging to the Turonian deposits of Orapa Pipe, Botswana. Most of the North American Sapindopsis species together with other taxa (i.e. Fontainea Newberry, Rhus L.) were included by Crabtree (1987) in the Sapindophyll morphotype. Again, this morphotype includes even to odd pinnatifid or pinnately compound leaves, a feature that excludes the palmately compound (trifoliate) specimens of Puesto Manuel Arce. Among the records of Sapindopsis, the Manuel Arce Formation specimens have similarities with Sapindopsis minutifolia Upchurch et al. (1994) from the upper Albian of Potomac Group, United States. This species typically has at least five leaflets in contrast with the three (or four) of the Manuel Arce specimens. However, both share the shape of their lamina, type of margin and gross venation features. Other species with leaflets comparable to those of Manuel Arce are from the middle Albian Pasayten and Winthrop Formations (United States) which are mentioned by Crabtree (1987, figures 27e32) as Sapindopsis sp. The species Sapindopsis belviderensis Berry exhibits a very large range of morphology. Although with an odd pinnate leaf organization, the leaflets in the fully dissected specimens of Winthrop Formation (Miller, 2007) also have similarities to those of Puesto Manuel Arce. Also from the Winthrop Formation, the species “Sapindopsis ternata” Miller and Hickey (in Miller, 2007) consists of a trifoliate leaf with leaflets of similar features, although with a higher density of teeth and a distinctive secondary venation. The genus Crassidenticulum Upchurch and Dilcher (1990) includes simple or compound leaves with predominately toothed margins from the Albian e Cenomanian of North America (Upchurch and Dilcher, 1990; Wang, 2002; Wang and Dilcher, 2006). Some of them have similarities to the leaves of Puesto Manuel Arce. This is the case of the most dissected trilobate specimens of Crassidenticulum trilobum Wang and Dilcher (2006), including a leaf from Hoisington III locality described by Wang (2002, figure 36.2), and two others specimens from the same locality mentioned by this author as “Crassidenticulum variloba” Wang (2002, figures 34.1 and 36.1). The Debeya group sensu Krassilov et al. (2005) consists of a heterogeneous set of palmate, pedate and trifoliate leaves from the Late Cretaceous assemblages of the Northern Hemisphere. This informal group includes numerous species referred to leaf-genera as Debeya Miquel (including Dewalquea), Retrodewalquea Krassilov, Eudebeya Krassilov and Platydebeya Krassilov (Krassilov et al., 2005; Halamski, 2013; Halamski and Kvacek, 2013). The last two genera proposed by Krassilov consist of compound, trifoliate to simple trilobate leaves with toothed margins. The specimens of Puesto Manuel Arce are similar to them in gross physiognomy (i.e. with Debeya tikhonovichii (Krishtofovich) Krassilov). The species Platanus bella (Heer) Kvacek et al. (2001) consists of trifoliate leaves with preserved cuticle and circumboreal Paleocene records. However, as with the Debeya group, the absence of epidermal characters and details of venation in the Patagonian specimens do not allow for a better comparison. Botanical affinity. A platanoid affinity has been suggested for Sapindopsis foliage on the basis of their cuticular features, and the usual co-ocurrences (although not attached to leaves) of Platanuslike inflorescences (i.e. Crane et al., 1993). Some morphotypes of Debeya group have been also linked to Platanaceae (see discussion in Krassilov et al., 2005) while, at least for one fossil species, differences to this family have been pointed out (i.e. Debeya tikhonovichii (Kryshtofovich) Krassilov in Kva cek et al., 2001). Although the gross morphology of cf. Sapindopsis is comparable to fossil forms mostly linked to a platanoid linage, this botanical affinity is

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improbable in the case of the palmately compound leaves of Puesto Manuel Arce, due to the northern hemisphere distribution of both extant and fossils Platanaceae. Crassidenticulum, the other fossil genus compared is considered as belonging to Magnoliidae (Upchurch and Dilcher, 1990; Wang and Dilcher, 2006). Leaves 3e5foliate are present in the extant Southern Hemisphere Raukaua clade (sensu Mitchell et al., 2012, Araliaceae) with species whose serrate leaves are comparable to cf. Sapindopsis as for example Raukaua laetevirens (Gay) Frodin and Raukaua simplex (G.Forst.) A.D.Mitch., Frodin and Heads. For the time being, following Halamski (2013), the palmately compound leaves of Puesto Manuel Arce may be considered to belong to the Eudicotyledoneae. Due to the absence of higher order venation and epidermal details, a more accurate systematic position cannot be determined.

4.1.5. Even-pinnately compound morphotype Genus. Dicotylophyllum auct. non. (used in the sense of Halamski, 2013). Dicotylophyllum sp. 2 Figs. 9B and 10AeB Studied material. MPEF-Pb-Mz 6719 (from DE1). Description. Fragmentary leaf even-pinnately compound, at least Notophyll in size. Leaf attachment not preserved. Leaflets (only four preserved) opposite to subopposite, petiolulate with microphyll size at 3e5 cm long and 0.7e1.3 cm wide (ratio L:W 3.7e4.5:1). Laminar shape elliptic to ovate with medial width symmetry and basal insertion either symmetrical or asymmetrical. Leaflets with margin untoothed, apex acute, convex to acuminate (without drip tip) and base acute to obtuse, convex in shape. Primary venation pinnate; mid vein stout to massive in size and with straight course. Naked basal veins not visible. Major secondary veins apparently eucamptodromous. Secondaries (at least 5 pairs) opposite to alternate, irregularly spaced, attached with acute angle (40e55 ) mostly uniform and with a slightly curved course. Relative thickness of secondary veins fine to hairlike. Venation of tertiary and higher order not clearly distinguishable. Remarks. This morphotype is represented by a single sample. The line-drawing (Fig. 9B) was reconstructed on the basis of this single impression and its counterpart. The secondaries are not visible near the margin possibly by attenuation of their gauge. This fact and the course of secondary veins support the supposition that secondaries do not reach the margin. Secondary marginal loops are not observed. In a basal leaflet the basal secondary vein presents an admedial ramification (see black arrowheads in Fig. 9B). Comparisons. Composite leaves have been previously recorded in southern South America from the Aptian La Cantera Formation (LC-Microphyll trifoliate, Puebla, 2009) and the upper Albianelower Cenomanian Kachaike Formation (Kachaikenia compuesta Cúneo and Gandolfo, 2005). However none of these records bears resemblance to Dicotylophyllum sp. 2 in either the leaflets' shape or venation. Furthermore, Dicotylophyllum sp. 2 differs from these records by consisting of an even-pinnately compound leaf. Although there are no other Cretaceous records of compound leaves in southern South America, leaves have been described that resemble disarticulated leaflets of Dicotylophyllum sp. 2, for example those included in the MA100 morphotype of Cenomanian e Coniacian Mata Amarilla Formation (Iglesias et al., 2007). The pinnately compound leaf organization also has Early Cretaceous records in the Northern Hemisphere (i.e. Asiatifolium elegans Suo, Guo and Zheng emend. Sun and Dilcher, 2002 from the ValanginianeHauterivian Chengzihe Formation and Sapindopsis spp.

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Fig. 10. Even-pinnately compound and fragmentary dicot leaves from the Puesto Manuel Arce Formation. AeB. Dicotylophyllum sp.2 (see also Fig. 9B) (MPEF-Pb-Mz 6719). C. Dicotylophyllum sp. 3 (see also Fig. 9E) (MPEF-Pb-Mz 6679). DeE. Dicotylophyllum sp. 4 (see also Fig. 9C) (MPEF-Pb-Mz 6722). F. Dicotylophyllum sp. 5 (see also Fig. 9D) (MPEF-Pb-Mz 6744). Scales AeC ¼ 1 cm; DeF ¼ 0.5 cm.

from the Albian of North America, Hickey and Doyle, 1977; Upchurch et al., 1994 and AlbianeCenomanian of Eurasia, Golovneva, 2007). Dicotylophyllum sp. 2 and Asiatifolium elegans consist of leaflets with short petiolules, lamina more or less elliptic (to ovate in Dicotylophyllum sp. 2 and obovate in A. elegans), with untoothed margin and at least 5 pairs of secondaries arising at acute angle (about 40e50 ) with a course slightly curved. The secondaries, poorly preserved, of Dicotylophyllum sp. 2 are apparently eucamptodromous and unforked, while in A. elegans they are brochidodromous and exmedially forked two or three times. As mentioned above the genus Sapindopsis Fontaine emend. Dilcher and Basson (1990) is characterized by even to odd pinnatifid or pinnately compound leaves, leaflets may be both sessile or with a short petiolule, elliptical to lanceolate-shaped, with untoothed (mostly) or toothed margin, a stout midrib extending to the apex of each leaflet and secondaries diverging from the midrib at various angles and patterns. Sapindopsis differs from Dicotylophyllum sp. 2 in that it commonly includes leaflets with a notably higher L:W ratio and, as mentioned by Dilcher and Basson (1990), with lamina decurrent to the leaf rachis (especially in the apicalmost leaflets). Botanical affinity. Halamski (2013) suggested that compound leaves are diagnostic for eudicots. Most extant angiosperms with pinnately compound leaves are in the Rosidae (Doyle, 2007).

Other morphotypes At least three other angiosperm mophotypes are present in the assemblage. They consist of single and fragmented leaves, mostly with only lower order veins preserved, which prevents comparison with other taxa. However, in spite of this, they have distinctive features that segregate them from the other foliar types described and illustrate the richness of angiosperms in the taphocenoses. 4.1.6. Serrate morphotypes Genus. Dicotylophyllum auct. non. (used in the sense of Halamski, 2013). Dicotylophyllum sp.3 Figs. 9E and 10C Studied material. MPEF-Pb-Mz 6673 and 6679 (from DE2). Description. Fragment (4 cm long and 2.5 cm wide) from the mid zone of a leaf with pinnate craspedodromous venation, characterized by a serrate margin consisting of teeth with a deeper and rounded sinus. Teeth with acute (spinose?) apex, the distal flank concave and the proximal one retroflexed. Teeth vascularized by a principal (secondary) vein that terminates at the tooth apex; no accessory veins are observed. Midvein stout in size and secondaries (3 subopposite pairs observed) straight to slightly curved, with relative thickness moderate.

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Dicotylophyllum sp.4 Figs. 9C and 10DeE Studied material. MPEF-Pb-Mz 6722 (from DE1). Description. Small fragment from an apical section of a leaf with pinnate craspedodromous venation and toothed (serrate) margin. Midvein moderate in size and secondaries (4 pairs observed) with relative thicknes moderate. Teeth with angular sinus, distal flank straight to flexuous and proximal flank flexuous, vascularized by a principal (secondary) vein that terminates at the tooth apex; no accessory veins are observed. Remarks. The shape of teeth clearly distinguishes this leaf from the rest of the taphocenoses. The irregular surface of the impression gives a false idea of a sympodial primary vein and sinuous secondaries. 4.1.7. Untoothed brochidodromous morphotype Genus. Dicotylophyllum auct. non. (used in the sense of Halamski, 2013). Dicotylophyllum sp.5 Figs. 9D and 10F Studied material. MPEF-Pb-Mz 6744. Description. Small fragment of a leaf characterized by untoothed present margin, secondary venation brochidodromous and intercostal tertiary vein fabric reticulate. Midvein moderate in size and secondaries (4 pairs observed) with relative thickness moderate. Base and apex not conserved. Remarks. This leaf fragment could be interpreted as a lamina portion of the previously described Araliaephyllum sp. However, it is distinguished by the different thickness (gauge) of the primary vein. 4.2. Non-angiosperm component A small number of ferns (Adiantites, Phyllopteroides, Cladophlebis) and conifers (Brachyphyllum, Elatocladus and a variety of indeterminate cuticles) complete the assemblage recovered from Puesto Manuel Arce Formation. They are represented by a few specimens with varying degrees of preservation. In spite of this, some taxa are described here due to the interesting Gondwana links that they suggest (i.e. Adiantites sp.) and because they illustrate the subordinate elements of this angiosperm dominated taphocenoses. Class Polypodiopsida (¼Filicopsida) Cronquist, Takhtajan and Zimmerman ex Reveal, 1995 Order incertae sedis € eppert, 1836 emend. Kidston, 1923 Genus. Adiantites Go € eppert, 1836 Type species. Adiantites oblongifolius Go Adiantites sp. Fig. 11AeD, FeG Material studied. MPEF-Pb-Mz 6674 and 6678 (from DE2), 6703, 6722 and 6728 (from DE1). Description. Fragments of leaves, pinnate in at least one specimen. The longest (MPEF-Pb-Mz 6674, Fig. 11B, G) around 2.5 cm in length, consisting of at least four lateral incomplete pinnae. The apparent decrease in size of pinnae toward the apex suggests that this specimen possibly represents a segment proximate to the terminal part of a leaf. Pinnae apparently alternate or sub-opposite disposed on rachis, with flabellate laminae and toothed distal margin. Teeth very small, with proximal and distal flanks concave

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or straight. The specimen MPEF-Pb-Mz 6703 (Fig. 11A, CeD, F) is interpreted as a basal pinnae with a short petiolule, concave base, and laminae divided in three main cuneiform lobes. Pinnae vascularized by a single main vein that divides dichotomously several times (at least four) at low angle and approximately equal distances, reaching the margin without anastomosing. Each veinlet terminates at the tip of a distal tooth, 1e2 veins per millimetre along distal margin. Remarks and comparisons. Two genera, Adiantites (Goepp.) emend. Kidston (1923) and Adiantopteris Vassilevskaja et al. (1963) have been commonly adopted to encompass sterile fossil leaves similar to those of the extant fern Adiantum L. The genus Adiantites € eppert (1836) and later more closely was originally erected by Go circumscribed by Kidston (1923) to include Palaeozoic fronds with presumably pteridophytic affinity but also encompassing gymnosperm forms (Mays et al., 2015). In spite of this, Adiantites was also employed for Mesozoic fronds (i.e. Douglas, 1973; Drinnan and Chambers, 1986; Mays et al., 2015). Wagner (2001) proposed to accept the genus Adiantites as emended by Kidston, although he remarked on the problematic nature of this genus in relation to other taxa commonly adopted for Palaeozoic leaves (i.e. Aneimites). On the other hand, the genus Adiantopteris was proposed by Vassilevskaja et al. (1963) to encompass Mezosoic-Neogene Adiantum-like fronds. It were mostly employed for leaves from the Upper Jurassic-Cretaceous Eurasian assemblages (i.e.Vakhrameev, 1991; Deng, 2002; Bugdaeva et al., 2006), although it has been also mentioned in the Cretaceous of Patagonia (Cladera et al., 2007). As pointed out by Mays et al. (2015), both fossil genera (Adiantites and Adiantopteris) have a relatively similar definition. Due to that Adiantites has priority; this genus was preferred by those authors, criterion that is also followed here. However, coinciding with Mays et al. (2015) the choice between the genera Adiantites or Adiantopteris is ambiguous and a nomenclatural revision is needed. Based on the shape (and apparent arrangement) of the pinnae, with distal small teeth, the venation pattern and also its dimensions, Adiantites sp. of the Puesto Manuel Arce Formation is possibly the same, or at least a related taxon to what Mays et al. (2015) describes as Adiantites sp. from the Tupuangi Formation (Cenomanian-Turonian) of New Zealand. Both species belong to deposits of the same age. In turn, there is a strong similarity with the more complete specimens described as Adiantopteris tripinnata
Formation (Aptian), Cladera et al. (2007) from the Anfiteatro de Tico Argentina. Adiantites dispersus Douglas (1973) from the Lower Cretaceous of Australia also has similar pinnules. Sphenopteris warragulensis McCoy consists of sterile and fertile fronds with records cited from the earlyemid-Cretaceous of
rctica and including a large list of synonymies Australia and Anta (Douglas, 1973; Drinnan and Chambers, 1986; McLoughlin et al., 1995; Cantrill and Nagalingum, 2005). Their pinnae include narrow and wide forms. Adiantites sp. from Puesto Manuel Arce has some superficially resemblance only with the wide forms described from the Albian of Antarctica (Cantrill and Nagalingum, 2005). In any case, the fronds of Puesto Manuel Arce consist only of sterile segments and neither were found narrow forms that suggest some connection with Sphenopteris warragulensis. Botanical affinity. A Polypodiopsida affinity is presumably suggested for this leaf. Furthermore, there are strong similarities with extant species belonging to Anemiaceae, for example Anemia adiantifolia (L.) Sw. The extant family Anemiaceae sensu Smith et al. (2006) consists of one genus (Anemia, incl. Mohria) with over 100 spp. mainly from the tropics of America. Flabellate pinnules with similar physiognomy and venation are also present in the

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Fig. 11. Fern leaves from the Puesto Manuel Arce Formation. AeD, FeG. Adiantites sp. A. Pinnae with a short petiolule (arrowhead) (MPEF-Pb-Mz 6703). B. Segment of leaf with incomplete lateral and apical pinnae (MPEF-Pb-Mz 6728). CeD. Details of two marginal areas of the pinnae figured in A, showing veins ending in very small teeth. FeG. Line drawing of the pinnae figured in A and B respectively. E, H. Phyllopteroides sp. E. Incomplete pinnae, with margin entire, prominent midrib and lateral veins dichotomized one time. H. Line drawing of the pinnae figured in E. Scales AeB, EeH ¼ 0.5 cm; CeD ¼ 0.1 cm.

cosmopolitan (mostly Neotropical) extant genus Adiantum L. (Pteridaceae). Genus. Phyllopteroides (Medwell) emend. Cantrill and Webb 1987 Type species. Phyllopteroides dentata (Medwell) Cantrill and Webb 1987. Phyllopteroides sp. Fig. 11E, H

Material studied. MPEF-Pb-Mz 6708. Description. Fragment of the basal portion of a pinnule, elongated, with margin entire, 1.8 cm long and around 1 cm width. Base partially preserved, acute, attenuate. Midrib prominent, with almost 0.5 mm thickness, straight. Lateral veins thin, straight to slightly recurved, diverging at 50e60 , dichotomizing once at low angle at varying distances of the midrib, although mostly in the first half of its course (and even at midrib). There are also some

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apparently unbranched veins. Lateral veins parallel, not anastomosing, 18e19 veins per cm of margin. Comparisons. Despite its fragmentary character, the features described fit within the constraints of Phyllopteroides (Medwell) emend. Cantrill and Webb (1987). This genus includes records from the Early to mid-Cretaceous of Gondwana, mostly from Australia, but also from Antarctica, New Zealand, India and Argentina (see review and species comparisons in Cantrill and Nagalingum, 2005, and also Passalia, 2007 and Parica et al., 2007). Botanical affinity. A Polypodiopsida affinity is presumably suggested for this leaf. An osmundaceous affinity has been suggested by Cantrill and Webb (1987) for at least one record of Phyllopteroides (P. dentata). Phyllum Pinophyta (¼Coniferophyta) Cronquist, Takhtajan and Zimmerman ex Reveal, 1995 Order incertae sedis Genus. Brachyphyllum Brongniart emend. Harris 1979 Type species. Brachyphyllum mamillare Brongniart 1828 Brachyphyllum sp. cf. B. irregulare Archangelsky 1963 Fig. 12AeD Material studied. Dispersed cuticles from DE1. Description. Leaf scale-like, probably adpressed, with rhomboidal to oval leaf base cushion and acute apex. Free part of leaf 1/4 to 1/3 of total length. Leaf size about 1.5 mm long and 0.5 mm broad. Cuticle thick. Leaf margin macroscopically entire, but with distinct projection of marginal cells giving a microscopically serrate aspect in the distal zone. Epidermal cells isodiametric (25e40 mm) to rectangular (until 75 mm long). Periclinal cell walls usually smooth; anticlinal cell walls straight and thick. Hypodermal cell remains longitudinally elongated and cutinized. Only a few stomata present on both leaf sides, dispersed, covering the totally of the epidermal surface, without an apparent order. Stomata typically monocyclic. Subsidiary cells (4e5), isodiametric to polygonal not usually not differentiated in polar and lateral. Subsidiary cells of neighbouring stomata occasionally in contact. Florin ring well developed. Guard cells slightly sunken, partially preserved. Mouth of pit oval to rounded, variably orientated. Comparisons. The features of these leaves fit with the diagnosis of Brachyphyllum emended by Harris (1979). Although the material is scarce, it is possible to make a brief comparative analyses with previous Brachyphyllum records from Patagonia. Among them, the Puesto Manuel Arce leaves are comparable with Brachyphyllum irregulare Archangelsky (1963) from the Anfiteatro de
Formation (Aptian). This is supported mainly by the irreguTico larly dispersed, scarce stomata that do not form rows, which are distinctive features of this species. Other characters in common are the number of subsidiaries, usually not differentiated in polar and lateral, although this feature is shared with other Brachyphyllum species of Patagonia. Two other species from Patagonia consisting of Brachyphyllum-leaf type also have sparse stomata: B. menendezii Herbst (Lower Jurassic) and Athrotaxis ungeri Halle emend. Archangelsky (Lower Cretaceous). However, their stomata are restricted to the adaxial cuticle or very rarely at the base of the abaxial one in A. ungeri (Archangelsky, 1963), and mainly developed at base of the abaxial cuticle in B. menendezii (Herbst, 1980). Genus. Elatocladus Halle 1913 Type species. Elatocladus heterophyllus, Halle, 1913 Elatocladus sp. Fig. 12EeG

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Material studied. MPEF-Pb-Mz 6706, 6749 (from DE1). Description. Short branch fragments, bearing linear and flattened leaves apparently spirally inserted, at about 40e60 , apex acute, base decurrent and margin entire. Leaf size about 5 mm long and 0.5e1 mm broad. Cuticle not preserved. Comparisons. In spite of their scarcity and poor preservation, these specimens can be accommodated in the fossil-genus Elatocladus as defined by Halle (1913: 83) for sterile coniferous branches of the radial or dorsi-ventral type. Reliable records of this genus occur from the latest Triassic to the Late Cretaceous, with possible occurrences during the Paleogene (Miller and Hickey, 2010). 5. Discussion In spite of the extensive outcrops of the Chubut Group as well as its length of time of deposition (Aptian e Cenomanian/early Turonian?), the scarcity of fossil plants yielded thus far is remarkable. On the other hand, the knowledge of the Patagonian floras during the CenomanianeSantonian is based on only a few previous records. In this context, a new Late Cretaceous plant assemblage from the Puesto Manuel Arce Formation (Chubut
rez et al. (2014), Group) is described here for the first time. Sua suggested a Cenomanian (97.4 ± 0.8 My) or less likely an earliest Turonian age (92.6 ± 1.5 My) for these deposits. During this time, hot greenhouse climate conditions with a low latitudinal thermal gradient have been proposed (i.e. Clarke and Jenkyns, 1999; Huber et al., 2002). The taphocenosis consists mostly of leaves preserved as impressions; although a variety of cuticle remains are also present. The fossil plants were collected from two sites which correspond to the same stratigraphic level, in sediments that were deposited in a lacustrine environment, alternating with an incipient fluvial environment. Angiosperms are the main component of the flora both in number of taxa (at least 9 leaf morphotypes recognized) and relative abundance (around 90%). A few ferns (Adiantites sp., Phyllopteroides sp., Cladophlebis sp.) and conifers (Brachyphyllum sp. cf. B. irregular, Elatocladus sp.) complete the remaining 10% of the plant assemblage. In general terms, the flora has features that are consistent
rez et al. (2014) for these deposits. with the age obtained by Sua This is based on the relative richness of angiosperm taxa and the features (with well-defined venation patterns not less than rank 2 or 3 in the sense of Hickey, 1977) and diversity of the leaf morphotypes recognized. In this sense, the angiosperm component can be included in the evolutionary stage 3 of Archangelsky et al. (2009), characterized by a progressive increase in both diversity and relative abundance of the flowering plants in Patagonia. The angiosperm leaves' physiognomy is notably diversified in comparison with the richness of taxa recognized, with no morphological feature more clearly represented than another. They consist of both simple as well as pinnately/palmately compound leaves, mostly microphyll to notophyll in size; lamina lobed or unlobed, margin toothed or entire and with a variety of venation types. This morphological heterogeneity persists when the angiosperm composition of the two lenses (DE1 and DE2) are analyzed separately. This suggest a plant community with some degree of complexity, possibly with taxa differentially exploiting resources by occupying different niches. The fossil assemblages from DE1 and DE2 have a different composition, sharing only a palmately compound leaf type (cf. Sapindopsis), and the fern Adiantites sp. While DE1 level is dominated by the oblong entire leaves of Myrtoidea sp., in the DE2 level

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Fig. 12. Conifer leaves from the Puesto Manuel Arce Formation. AeD. Leaf cuticle of Brachyphyllum sp. cf. B. irregulare (MPEF-Pb-Mz) in inner view, observed under transmitted-light microscope. A. General aspect of abaxial (left) and adaxial (right) cuticle. B. Abaxial cuticle with three stomata. Black arrowheads indicate remnants of hypodermal cells. C. Abaxial cuticle showing stomata dispersed, without an apparent order. D. Abaxial cuticle showing a stoma with a well-developed Florin ring (black arrow) and possible remnants of a guard cell. EeG. Elatocladus sp. (MPEF-Pb-Mz 6749). E. Fragment of an axis bearing linear and flattened leaves. FeG. Details of the white square areas indicated in Fig. E. White arrowhead pointed out the position of some leaves. Scale A ¼ 0.5 mm; BeC ¼ 100 m; D ¼ 50 m; E ¼ 5 mm; FeG ¼ 2 mm.

the most abundant taxon is the palmatilobed Bamfordphyllum crassivena. Although both fossil lenses belong to the same stratigraphic level, it is possible that a slight difference in age exists between them due to a differential erosive process at the time of the initiation of a high-energy fluvial system of the overlying Salamanca Formation. In this case, floral change occurring within a short time-slice may explain the differences observed in their composition. Another possibility is that the variation in the taxonomic composition of both lenses may reflect true horizontal differences between two patches of vegetation developed simultaneously in slightly different facies: an incipient fluvial system for DE1, and a genuinely lacustrine facies for DE2. Radical horizontal floral changes across short distances, associated to different facies or successional stages, have been previously mentioned for Late Cretaceous floras (i.e. Parker, 1976 in Wing and Tiffney, 1987; Wing et al., 1993). This calls into question the value of using isolated floristic assemblages as matching biostratigraphical tools.

The presence of compound leaves (trifoliate and paripinnate) is highlighted, including two novel morphotypes for the Cretaceous of Patagonia (cf. Sapindopsis, Dicotylophyllum sp. 2). From a palaeoecological point of view, Givnish (1979) notes that compound foliage tends to occur on many early successional trees and shrubs or disturbed vegetation, being an advantageous strategy of rapid colonization of the space with low investment of resources. This leaf organization might also reduce transpirational water loss during seasonal droughts by abscission of the supporting rachis. Three morphotypes consist of palmatilobate leaves (Bamfordphyllum crassivena, Dicotylophyllum sp. 1 and Araliaephyllum sp.). According to Nicotra et al. (2011, and cites therein), in addition to reducing heat loads, the morphology of deeply lobed leaves may also reflects direct selection for increased hydraulic efficiency and has been suggested as an adaptation to dry conditions. Deeply cordate leaves (as Dicotylophyllum sp.1) are frequently found on vines or forest floor herbs and shrubs (Givnish, 1979).

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Another remarkable taxon of this flora is Myrtoidea sp., which dominates the DE 2 lens. Leaves of myrtophyll physiognomy are known from the Cretaceous in both hemispheres (see above). However, while in the Northern Hemisphere, it is just another element in angiosperm-dominated floras with certain grades of diversification, the myrtophyll is a particularly recurrent component along the Albian?eMaastrichtian assemblages of southern South America, being especially diversified since the Paleogene. In Antarctic Peninsula this morphotype is known at least since the CampanianeMaastrichtian (Dutra and Batten, 2000) and is also a characteristic element in Paleogene assemblages (Dutra, 2004). Certain taxa of the Puesto Manuel Arce assemblage are similar to some from the Patagonian flora of Mata Amarilla (CenomanianeConiacian) previously described by Berry (1928, 1937), Frenguelli (1953) and more recently by Iglesias et al. (2007). Bamfordphyllum crassivena resembles some specimens enclosed in the MA106 morphotype of Iglesias et al. (2007), and a fragmentary leaf of Sterculia washburnii of Berry (1928). Myrtophyll leaves, although with differences in respect to Myrtoidea sp., are also present in the Mata Amarilla flora (Myrcia santacruzensis, MA103 and possibly MA104-105 morphotypes) as well as a fern comparable to Adiantites sp. (see text-fig. 10 AeB of Iglesias et al., 2007 and pers. obs.). Myrtophyll leaves, with two taxa (Myrtoidea patagonica and Myrtoidea sp., Passalia et al., 2001), are the dominant elements in another Cretaceous Patagonian assemblage from Bajo de los Corrales (?AlbianeCenomanian). A fern leaf fragment from this locality (Polypodiidae incertae sedis, fig. 4B in Passalia et al., 2001) has some resemblance to Adiantites sp. of Puesto Manuel Arce. Two elements from the Puesto Manuel Arce flora (Adiantites sp. and Bamfordphyllum crassivena) have notable resemblance to species previously recognized in other Gondwanan floras. They are the fern Adiantites sp. from the Tupuangi Formation (CenomanianTuronian) of New Zealand (Mays et al., 2015) and the angiosperm leaf “Robustavena lobata” from the Turonian deposits of Orapa Pipe, Botswana (Bamford, 1989). It is possible that both Adiantites sp. from Patagonia and New Zealand, as well as Bamfordphyllum crassivena/“Robustavena lobata”, belong to the same natural group (conspecific), or at least to related taxa. The shared presence of the fern Adiantites between the Puesto Manuel Arce and Tupuangi Formations is not surprising because both deposits are possibly coeval (Cenomanian-Turonian) and on the other hand, because during this time-slice the New Zealand taphoflora was placed adjacent to West Antarctica (Mays et al., 2015). In consequence, if it is assumed as a natural group, Adiantites may have been widely distributed between Patagonia and New Zealand throughout Antarctic Peninsula. This hypothetical distribution is supported by the low latitudinal thermal gradient estimated for this time (Huber et al., 2002). Furthermore, in older deposits (upper Albian), the presence of Adiantites (as cf. Adiantites) in the Antarctic Peninsula was mentioned by Cantrill (1997). Mays et al. (2015) mentioned that the macrofloral record of the Tupuangi Formation also includes conifers, Ginkgoales and angiosperms. Future comparative studies between the Tupuangi and Puesto Manuel Arce flora may show other similarities, especially regarding the angiosperms. The other interesting similarity occurs between the Patagonian leaves here named Bamfordphyllum crassivena and those from Botswana previously described as “Robustavena lobata” Bamford (1989). We found that this leaf morphotype is comparable, in part, to leaves previously described from the Cretaceous of Patagonia (i.e. Mata Amarilla flora) and with the exception of the Orapa Pipe flora of Botswana, it is, as far as we know, absent in other Gondwanan and possibly extra-Gondwanan Cretaceous floras. The similarity between the specimens from both

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(Patagonian and African) sources may simply mean some kind of morphological convergence among unrelated taxa or perhaps suggests some kind of taxonomic link. Both species belong to deposits whose ages are Turonian (or slightly older for the Patagonian one). For this time, southern South America and southern Africa are separated by a wider Atlantic Ocean which begins to open during the Early Cretaceous (i.e. Scotese, 2004). If a taxonomic relationship between B. crassivena and “R. lobata” is assumed, their disjunct distribution on both sides of the South Atlantic may be explained by long-distance dispersal. In this sense McLoughlin (2001) notes that it is likely that floristic interchange between isolated landmasses was even more common during the Cretaceous and Paleogene when more equable global climates prevailed and intercontinental distances in the Southern Hemisphere were less than at present. Furthermore, Ezcurra and Agnolín (2012) point out that the divergence times between several South American and African extant plant and animal groups suggest dispersal events between both landmasses after their complete severing (around the SantonianeCampanian, according to Scotese, 2004). In any case, more studies of midCretaceous floras from southern South America and southern Africa are necessary to support them. Megafloras of the upper Albian e lower Cenomanian of Patagonia (Kachaike Formation, Cúneo and Gandolfo, 2005; Passalia, 2007) and Antarctic Peninsula (Neptune Glacier Formation, Cantrill, 2001) have an angiosperm component that exhibit a good diversity of taxa, which possibly occupied a variety of niches for that time. However, the angiosperms in these floras remain a minor component in assemblages characterized by a high participation of gymnosperms (even including bennettites) and pteridophytes. A similar composition was observed in the uppermost Albian e Cenomanian Winton Formation flora of north eastern Australia, which occupied an equal paleolatitude to those coeval floras of Patagonia (see McLoughlin et al., 2010 and cites therein). In this sense, according to the relative participation of the angiosperms in the taphocenosis, the Puesto Manuel Arce assemblage appears to be more comparable to the angiosperm dominated CenomanianeConiacian flora of Mata Amarilla, Patagonia (Iglesias et al., 2007 and cites therein) rather than those Gondwana floras previously mentioned. The assemblage also shares some morphotypes with the Mata Amarilla flora as discussed above. Finally, the relationship of the Puesto Manuel Arce assemblage to two other mid- to Late Cretaceous floras of Patagonia, as those of Castillo and Portezuelo formations (middle Albian e lower Cenomanian and upper Turonian e lower Coniacian, respectively) remains to be explored. Both cases consist of angiosperm dominated assemblages with around fifteen leaf morphotypes recog
ndez, 1959; Romero, 1977; Passalia nized (Frenguelli, 1930; Mene et al., 2000, 2008; Llorens and Passalia, 2014). Some vague similarities have been mentioned between specimens of Puesto Manuel Arce (see comparisons in Araliaephylum sp. and Bamfordphyllum crassivena) and others from the Castillo and Portezuelo formations. However, these two latest floras are known from small collections. Future studies, based on new data, are necessary to highlight the relationships among all these Cretaceous floras of Patagonia. 6. Conclusions A new mid-Cretaceous plant assemblage from Patagonia, Argentina is described. It represents the first megafloristic record
-Can ~ ado
n Asfalto Basin, for the Chubut Group in the Somuncura corresponding to the Cenomanian (to earliest Turonian?) Puesto Manuel Arce Formation.

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The taphocenosis is dominated by angiosperm leaf impressions, with at least nine leaf morphotypes recognized. All of them consist of dicot leaves. Although their systematic position at Order level remains open, possible botanical affinities have been discussed. The angiosperm leaves exhibit physiognomical heterogeneity with a variety of well-defined venation patterns; suggesting a plant community with some degree of complexity. Among the angiosperms, two types of leaves stand out for their abundance. They are the myrtophyll morphotype (Myrtoidea sp.), a recurrent component along the Albian?-Maastrichtian assemblages of southern South America, and the palmatilobed palinactinodromous Bamfordphyllum crassivena gen. et sp. nov. A few ferns (Adiantites sp., Phyllopteroides sp., Cladophlebis sp.) and conifers (Brachyphyllum sp. cf. B. irregular, Elatocladus sp.) complete the plant assemblage. According to the relative abundance of the angiosperms in the taphocenosis (around 90%), the Puesto Manuel Arce assemblage is, at least partially comparable to the angiosperm dominated flora of Mata Amarilla, CenomanianeConiacian of southern Patagonia, with which it also shares some angiosperm morphotypes and a fern taxon. Two elements from the Puesto Manuel Arce (Adiantites sp. and Bamfordphyllum crassivena) notably resemble species previously recognized in other coeval Gondwanan floras. It suggests interesting links among mid-Cretaceous floras of Patagonia, New Zealand and southern African that should be explored in future work. The importance of this new assemblage recovered from Puesto Manuel Arce Formation, resides in the fact that allows incorporate, for the first time, palaeobotanical evidence regarding the angiosperm radiation from a Cretaceous basin never before considered, and from a time-slice with no abundant records in Patagonia. More evidence of Cenomaniane Santonian floras from southern South America is critical to increasing our understanding of the transformation of plant communities toward angiosperm dominated floras. Acknowledgments
sari for her support and This paper is dedicated to Dr. Silvia Ce constant encouragement. We thank the Ferrín family for their hospitality at Estancia Don Eduardo and to Alejandro Scagliotti for sketching the stratigraphic profile. We are also grateful to
sari and Georgina del Fueyo for discusEzequiel Vera, Silvia Ce sions on the choice of Adiantites/Adiantopteris genera. Thanks are extended to the anonymous reviewers for their comments, which improved the final version of the manuscript. This work was supported by ANPCyT (PICT 169 and 2602) and CONICET (PIP 512). References
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