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A Scincomorpha lizard from the Campanian of Patagonia
Cretaceous Research 32 (2011) 781e785
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A Scincomorpha lizard from the Campanian of Patagonia Santiago Brizuela*, Adriana Albino CONICET, Departamento de Biología, Universidad Nacional de Mar del Plata, Funes 3250, 7600 Mar del Plata, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 April 2010 Accepted in revised form 11 May 2011 Available online 20 May 2011
The terrestrial lizard fossil record of Gondwana is very scarce. Few lizards, from mostly fragmentary fossils, have been identified in Madagascar, Tanzania, Morocco, South Africa, India and South America. Among the South American specimens there are basal Squamata forms (Olindalacerta and Tijubina) and a possible iguanid (Pristiguana) form Brazil. In Argentina gondwanian terrestrial lizards are represented by a putative iguanid and a small, poorly preserved dentary. This last specimen, recovered from the Anacleto Formation (Neuquén Group, Río Colorado Subgroup) in vicinity of the locality of Cinco Saltos (Río Negro Province), is here described formally. Comparisons with extant lizards indicate more affinity of the fossil with the Scincomorpha (non Scincophidia) than with any other group of lizards. This finding suggests that lizards were probably better represented and more diverse in the Mesozoic of South America than previously thought, although the fossil record is, at the moment, much poorer than in Laurasia. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Squamata Lizards Scincomorpha Cretaceous Patagonia
1. Introduction Extant squamates (Squamata) constitute a successful group of reptiles that, according to osteological-based phylogenetic hypothesis (contra molecular-based ones e.g. Vidal and Hedges, 2009; see Conrad, 2008 and references therein), includes two main clades, the Iguania and the Scleroglossa (Iguanomorpha and Scincogekkonomorpha if fossils are considered). Although lizards (non-amphisbaenian, non-serpentian squamates) constitute the majority of the living squamates, they are not a monophyletic group (e.g. Estes et al., 1988; Conrad, 2008; Vidal and Hedges, 2009). Lizards natural history is ancient but little known, especially in gondwanian territories (Evans, 2003). In South America the lizard fossil record is limited to a few findings in the Cretaceous of Brazil and Argentina (Estes and Price, 1973; Bonfim and Marques, 1997; Evans and Yabumoto, 1998; Albino, 2002, 2007; Apesteguía et al., 2005; de la Fuente et al., 2007; Candeiro et al., 2009). The Neuquén Group is one of the richest sedimentary unit in fossil vertebrates of Patagonia (Leanza et al., 2004). Within the Neuquén Group, the Río Colorado Subgroup (the upper third part of the Neuquén Group) is made up of two Formations: the inferior Bajo de la Carpa Formation and the superior Anacleto Formation (Cazau and Uliana, 1973; Leanza and Hugo, 2001; Leanza et al., 2004) (Fig. 1). This last Formation was deposited between 83.5
* Corresponding author. E-mail addresses: [email protected] (S. Brizuela), [email protected] (A. Albino). 0195-6671/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2011.05.006
and 79.5 Ma ago, during the early Campanian (Dingus et al., 2000). Leanza et al. (2004) list the tetrapod fauna recovered from the Anacleto Formation, which includes titanosaurid, theropod and ornithischian dinosaurs as well as birds (icnites) and at least one mammalian taxon. Very few Squamata have been recovered from the Anacleto Formation; among them, there is the most modern record of the snake Dinilysia patagonica Woodward, 1901 (Albino, 2007). Lizards are represented in this Formation solely by a small, partial dentary recovered near the locality of Cinco Saltos, Río Negro Province (Fig. 1) (Albino, 2002, 2007). Given the poverty of lizard remains in the Mesozoic of Gondwana (Evans, 2003 and references therein), this finding is significant to understand the early evolution of squamates in these territories. Therefore, the aim of this paper is to describe and discuss the taxonomic affinities of this fossil.
2. Materials and methods The dentary was found by Marcos Poblete in the vicinity of the locality of Cinco Saltos, Río Negro Province, Argentina (Fig. 1). Because of the fragility of the fossil it was covered with abundant glue. Latter it was not possible to remove the glue without damaging the fossil given its poor fossilization state. The glue hinders the observation of some of the details of the dentary and prevents the use of electronic microscopy, particularly to analyze apical tooth morphology. The fossil was confronted directly with osteological material from a diverse group of present-day lizards and its systematic
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Fig. 1. Map of fossil site in vicinities of Cinco Saltos city (38 490 S, 68 040 W) (open circle) and stratigraphic column of the Neuquén Group. A) Río Negro province in gray; B) northwester section of Río Negro province (light gray), Neuquén Group outcrops in dark gray (modified from Ardolino et al., 1994); C) generalized stratigraphic column of the Neuquén Group (modified from Leanza et al., 2004). Figure Legend from left to right: National route; Provincial route; railroad; temporary river; paleosols; conglomerates; sandstones; siltstones; siliceous geodes; mudrocks; volcanic ash.
affinities were analyzed taking into account previously published data. Systematic follows Conrad (2008). 3. Systematic paleontology SQUAMATA Oppel, 1811 SCINCOGEKKONOMORPHA Sukhanov, 1961 EVANSAURIA Conrad, 2008 SCLEROGLOSSA Estes et al., 1988 SCINCOMORPHA Camp, 1923 (not Scincophidia) Gen et sp. indet. (Figs. 2 and 3)
3.1. Referred material Incomplete left dentary. The dentary is housed at the Museo Regional de Cinco Saltos (Cinco Saltos locality, Río Negro Province, Argentina) in the section Paleontología de Vertebrados under the acronym MCS-Pv 41. 3.2. Geographic and stratigraphic provenance Outskirts of the locality of Cinco Saltos (38 490 S, 68 040 W), Province of Río Negro, Argentina (Fig. 1). Anacleto Formation (Neuquén Group, Río Colorado Subgroup), early Campanian (Dingus et al., 2000) (Fig. 1). 3.3. Description The fossil corresponds to the middle-posterior part of a robust dentary, of regular size, and a total length of 10.69 mm. Its size is comparable with that of a similar portion of the dentary of an adult Timon lepidus (Daudin, 1802) (previously Lacerta lepida, maximun snout vent length in males ¼ 240 mm, Mateo and Castanet, 1994; figured in Estes et al., 1988: 212). The dentary is labially plane,
smooth and bears three mental foramina (inferior alveolar foramina of Gao and Fox, 1996) at a middle height and below the tooth positions (a), (d) and (h) (Fig. 2). The dorsal margin of the dentary is straight, whereas the ventral margin is convex, therefore the dentary is deeper posteriorly. The posterior end of the dentary is not preserved; no articulation facet for the anterolateral process of the coronoid is present on the preserved section of the dentary. Lingually, Meckel’s canal is medially opened. The important ventral development of the subdental shelf, whose maximum is achieved the midpoint of the conserved dental series, confines the anterior part of Meckel’s canal. Posteriorly, the subdental shelf tapers, not developing posterior to the (i) tooth position. Ventral on the subdental shelf the articulation facet of the splenial is poorly preserved, extending anteriorly to the (e) tooth position. The ventral border of the subdental shelf and that of the dentary are parallel and closed together in the anterior part of the conserved dentary. Ventral to the (i) tooth position, upon the roof of Mekel’s canal, is the internal foramen of internal mental canal (inferior alveolar canal of Gao and Fox, 1996). Tough cover by glue, there is no apparent posterior projection of the intramandibular septum (i.e. no intramandibular lamella, Smith, 2009). Dorsally on the dentary, developed upon the dental groove is the dental series. Between the bases of the teeth and the moderate subdental ridge of the subdental shelf there is a narrow space which is considered a shallow subdental gutter (i.e. sulcus dentalis). Though tooth bases cannot be adequately observed because of sediment and glue, tooth implantation is considered pleurodont since teeth have at least half their height attached to the labial parapet of the dental groove (pleurodoncy sensu Gao and Fox, 1996). Only 11 tooth positions are preserved, representing the posterior dentition. Teeth (a), (c) and (e) are missing, and only the base of tooth (b) is preserved. Among the remaining teeth, only (g), (h) and (i) are well-preserved. The last tooth (k) is broken, not preserving its distal half. Teeth are robust, firmly attached to the dentary. They are closely spaced and all of the same height, forming a close palisade. The bases of the teeth present a slight mesodistal compression and labiolingual development. The labial faces of the teeth are straight, vertical, whereas
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Fig. 2. Scincomorpha indet. (MSC-Pv 41) from the Anacleto Formation (Campanian) in the outskirts of Cinco Saltos city (Río Negro Province, Argentina). AeC, photograph in (A) labial, (B) lingual and (C) oclusal views. DeF, illustrations in (A) labial, (B) lingual and (C) oclusal views. Abbreviations: a.f.S, articulation facet for the splenial; M.c, Meckel’s canal; m.f, mental foramen; r.p, resorption pit; sb.s, subdental shelf; s.d, sulcus dentalis. Scale 5 mm.
the lingual faces are more oblique. Apically teeth are blunt, with a slight labialelingual compression. Detailed observation of tooth tips is not possible due to conservation and preparation factors. Nonetheless, teeth are unicuspid, with a convex apical outline (Fig. 3). No striae are observed. On the base of tooth (h) there is an important resorption pit which resembles the “iguanid replacement” of Edmund (1969). 4. Discussion
Fig. 3. Apical end of teeth (h) and (i) of fossil MCS-Pv 41. Scale 1 mm.
Albino (2002) first noted this fossil from the Anacleto Formation, tentatively relating it to the Teiidae (Scincomorpha). Latter, she considers that the fossil presents affinities with Pristiguana brasiliensis Estes and Price 1973 (Albino, 2007; de la Fuente et al., 2007), a lizard with Iguania or Teiidae affinities from the Cretaceous of Brazil (Estes and Price, 1973; Borsuk Bialynicka and Moody, 1984). The characters that the dentary from Anacleto Formation
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(MSC-Pv 41) shares with P. brasiliensis are: an anteriorly restricted intramandibular septum, a shallow subdental gutter, and the homodoncy where teeth are attached to the dentary with at least half their height. However, the fossil dentary differs from Pristiguana in not having clearly differentiated cusps on the teeth, whereas Pristiguana has a bluntly tricuspid condition (Estes and Price, 1973). Another difference between these fossils is that in the dentary MCS-Pv 41 Meckel’s canal closes more abruptly than in Pristiguana. Only 12 characters (C170, C171, C181, C182, C188, C211, C213, C214, C217, C219, C221, C225), a 2.3% of those presented by Conrad (2008), could be without doubt scored for fossil MSC-Pv-41. When Conrad’s (2008) data matrix þ MSC-Pv 41 was run in TNT (Goloboff et al., 2008), using the ratchet option set to find the shortest tree 1000 times, saving to RAM and performing two more ratchet analysis on the saved trees (initial part of Conrad’s (2008) protocol), MCS-Pv 41 appeared in a very large basal polytomy in the Strict Consensus (of 10 equally most parsimonic trees, length 3329). Therefore a more traditional character discussion is followed. Dentary MCS-Pv 41 presents a well-developed subdental shelf, a scleroglossan synapomorphy according to Estes et al. (1988). Following Conrad (2008) a subdental shelf is absent in Acrodonta and the scleroglossan Amphisbaenia and Serpentes. Within the Scleroglossa, the “iguanian tooth replacement” of the fossil dentary is indicating more affinity with the Scincomorpha (although not with Scinciformes: Conrad, 2008) than with the Anguimorpha (Edmund, 1969; Conrad, 2008). In this same regard, the intramandibular septum, which is here considered to be found anterior to the midpoint of the articulation of the splenial-angular and the last tooth preserved, is not found within the Anguimorpha. Anguimorpha and the Contogeniidae (Cenomanian-middle Paleocene Scincomorpha) are characterized by a well-developed intramandibular septum, with an important posterior development (Estes et al., 1988; Lee and Scanlon, 2001; Nydam and Fitzpatrick, 2009). This last condition is absent in the fossil specimen. Meckel’s canal of the fossil dentary is medially open, but it is quickly restricted anterior to the internal foramen of internal mental canal. A medially open Meckel’s canal differs from the close condition observed uniformly within the Gekkota and Xantusiidae, and in some species of other families (Estes et al., 1988; Conrad, 2008), like in the majority of the Gymnophthalmidae (Presch, 1980). Meckel’s canal of the studied fossil also differs from that of the Lacertidae and Teiidae where the canal is widely opened all along its extension. The restriction noted by Denton and O’Neill (1995) in the Teiinae Teiidae is more anteriorly restricted. Within the Scincoidea sensu Estes et al. (1988) (i.e. Cordylidae and Scincidae sensu lato) there is an important variation of this character, where Meckel’s canal can be alternatively closed, open or very restricted (Estes et al., 1988). According to Conrad (2008), only in Scelotidae and Scincidae among the Scincidae sensu lato, Meckel’s canal is partially closed as in the fossil dentary, while in Acontidae and Feylinidae (i.e. members of the Scincophidia) it is closed and fused. Tooth morphology varies greatly among Scincomorpha (sensu Estes et al., 1988) at specific and interspecific levels. One can (arbitrarily) distinguish three main basic tooth plans, where exceptions are common. One (1) in which the striae dominantes (see Richter, 1994) form a secondary lingual cusp, common amongst Mesozoic Paramacellodidae and most of the recent Gerrhosauridae and Cordylidae sensu stricto (Kosma, 2004). In an other plan (2), the secondary lingual cusp is formed by different system of cutting edges (cristae linguales) (particularly abundant in Scincidae sensu lato) (Kosma, 2004). In both of these cases the enamel presents distinct dominant striae, a plesiomorphic character of the Scincomorpha or possibly the Scleroglossa (Nydam and Fitzpatrick, 2009). The third type (3) is that present in the Lacertoidea where there are
Fig. 4. Midsection of the left hemimandible of Mabuya frenata (Universidad Nacional de Mar del Plata 1599). Abbreviations: aiaf, anterior interior alveolar foramen; sb.s, subdental shelf; Sp, splenial. Scale 2 mm.
no marked, distinct main striae (e.g. striae dominantes or cristae linguales), enamel is generally smooth (exceptions occur e.g. posterior teeth of adult Tupinambis) and cusp are meso-lingualy orientated (exceptions occur in some extant Teiinae Teiidae, e.g. Teius and Dicrodon, and in some Borioteiioidea, e.g. Dicothodon). Fossil MCS-Pv 41 does not fall clearly in any of these types. Teeth with a blunt apical outline differ from those present in the majority of Lacertoidea which have acute tooth tips with several cusps (Presch, 1974; Herrel et al., 2004). Moreover, their distribution forming a palisade of closely together teeth of same height differs from the condition observed in the most Teiioidea where teeth are spaced and not always of the same height. A similar tooth disposition as that of the fossil was observed in the present-day genus Mabuya (Scincidae), although in this genus teeth are somewhat more spaced (Fig. 4). The teeth of the fossil and Mabuya share blunt distal outlines, although the teeth of Mabuya present a more complex apical morphology (bicuspid teeth, with cristae lingualis). In light of the stated above, specially taking into account the abrupt anterior restriction of Meckel’s canal, the teeth in palisade, with a blunt distal outlines and laterally compressed, the fossil can be tentatively assigned to the Scincomorpha not Scincophidia. Among the extant representatives of the Scincomorpha the fossil further differs from the Xantusiidae (open Meckel’s canal) and Lacertidae (in basic tooth morphology and disposition). The fossil cannot be differentiated from Cordyliformes (Cordylidae sensu stricto and Gerrhosauridae), Scelotidae nor Scincidae. Yet tooth morphology differs from the general tooth plan observed in these taxa (see above). These lizard families closely resemble the Scincoidae of Estes et al. (1988), with the exclusion of Acontidae and Feylinidae of Conrad (2008). Estes et al. (1988) based their differentiation of families Scincidae sensu lato, Cordylidae and Gerrhosauridae on cranial and postcranial characters not conserved in the fossil. Furthermore it has been stated that it is difficult to distinguish them based on dentary characters alone (Krause et al., 2003). A straight ventral margin of the dentary (not observed in the fossil) is considered by some authors as indicative of Cordylidae affinities although this character is present in some Scincidae sensu lato (Krause et al., 2003). Therefore, the fossil cannot be evaluated at a lower taxonomic level. Compared with Konkasaurus mahalana Krause et al., 2003, the only other known Scincomorpha non-Scincophidia gondwanian taxon, MCS-Pv 41 is deeper and a presents simpler tooth morphology. 5. Conclusions The continental lizards of the Mesozoic of South America are represented by few records. The lower and middle Jurassic reference of lizards in Patagonia (Casamiquela, 1962, 1975, 1980; Rauhut et al., 2001; Rauhut and Puerta, 2001; Evans, 2003) and lower
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Cretaceous of northwest Argentina (Huene, 1931) are dismissed (Estes, 1983; Albino, 2007). Likewise, the report of a possible teiid in the Cretaceous of Chile (Gayet et al., 1992; Albino, 1996) has never been confirmed (Albino, 2007). Furthermore many of the possible teiid and iguanian remains from the late Cretaceous of Patagonia (Leanza et al., 2004; Albino, 2007) are not fossils. The most complete lizard specimens are those of the early-middle Cretaceous (AptianeAlbian) (Olindalacerta brasiliensis and Tijubina pontei) and late Cretaceous (Maastrichtian) (Pristiguana brasilensis) of Brazil, the former being basal forms of squamates of uncertain phylogenetic relationships (Estes and Price, 1973; Bonfim and Marques, 1997; Evans and Yabumoto, 1998), the latter a possible Iguanid or Teiidae (Estes and Price, 1973; Borsuk Bialynicka and Moody, 1984). A partial skeleton of an indeterminate non-serpentian squamate has also been recovered from the Maastrichtian of Brazil (Candeiro et al., 2009). In Argentina, the only other Mesozoic lizard fossil is a partial frontal from the Cenomanian assigned to the “Iguanidae” (Apesteguía et al., 2005). Consequently, the dentary from the Anacleto Formation described in this paper constitutes the first record of a Scincogekkonomorpha lizard in the Cretaceous of South America. The tentative assignation to the Scincomorpha nonScincophidia allows to hypothetize that the group was already present in gondwanian territories in the late Cretaceous. The presence of a probable Cordylidae in the Maastrichtian of Madagascar (Krause et al., 2003) supports this hypothesis. This finding suggests that the presence of lizards in the Mesozoic of South America is sub-evaluated because its fossil record is composed of small, very fragmentary elements which are of poor preservation, and have not been intentionally targeted in the different fossil bearing sites of South America. Acknowledgments We like to thank Leonardo Salgado who notices us about the fossil specimen described in this paper and Ignacio Cerda for facilitating the studied material. We also thank reviewers S. Apesteguía and M.E.H. Jones as well as Editor M.B. Hart for their comments and suggestions on the early version of this contribution. PIP-CONICET 112-200901-00176 financed this study. References Albino, A.M., 1996. The South American Fossil Squamata (Reptilia: Lepidosauria). In: Arratia, G. (Ed.), Contributions of Southern South America to Vertebrate Paleontology (A)30. Münchner Geowissenchaftliche Abhandlungen, München, pp. 185e202. Albino, A.M., 2002. El lagarto más antiguo de la Argentina. I Congreso “Osvaldo A. Reig” de Vertebradología básica y evolutiva e Historia y Filosofía de la Ciencia, Bs. As., 2002, p. 21. Albino, A.M., 2007. Lepidosauromorpha. In: Gasparini, Z., Salgado, L., Coria, R.A. (Eds.), Patagonian Mesozoic Reptiles. Indiana University Press, Bloomington, Indiana, pp. 87e115. Apesteguía, S., Agnolin, F.L., Lio, G.L., 2005. An early Late Cretaceous lizard from Patagonia, Argentina. Comptes Rendus Palevol 4, 311e315. Ardolino, A., Caminos, R., Chucci, R., Franchi, M., Leanza, H., Lizuain, A., Nullo, F., 1994. Mapa geológico de la provincia de Río Negro, República Argentina. Bonfim Jr., F., Marques, R.B., 1997. Um novo lagarto do Cretáceo do Brazil (Lepidosauria, Squamata, Lacertilia e Formaçao Santana, Aptiano da Bacia do Araripe). Anuário do Instituto de Geociencias 20, 233e240. Borsuk Bialynicka, M., Moody, S.M., 1984. Priscagaminae, a new subfamily of the Agamidae (Sauria) from the Late Cretaceous of the Gobi Desert. Palaeontologia Polonica 29, 51e81. Candeiro, C.R.A., Navas, C.A., Martinelli, A.G., Forasiepi, A.M., Scanferla, C.A., Muzzopappa, P., 2009. New lizard record (Diapsida, Lepidosauria) from the Upper Cretaceous Adamantina Formation, Brazil. Bulletin of Geosciences 84, 573e576. Casamiquela, R.M., 1962. Sobre la pisada de un presunto sauria aberrante en el Liásico del Neuquén (Patagonia). Ameghiniana 2, 183e186. Casamiquela, R.M., 1975. La presencia de un sauria (Lacertilia) en el Liásico de Patagonia austral. I Congreso Argentino de Paleontología y Bioestratigrafía, Actas, 57e70.
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A Scincomorpha lizard from the Campanian of Patagonia Santiago Brizuela*, Adriana Albino CONICET, Departamento de Biología, Universidad Nacional de Mar del Plata, Funes 3250, 7600 Mar del Plata, Argentina
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a b s t r a c t
Article history: Received 16 April 2010 Accepted in revised form 11 May 2011 Available online 20 May 2011
The terrestrial lizard fossil record of Gondwana is very scarce. Few lizards, from mostly fragmentary fossils, have been identified in Madagascar, Tanzania, Morocco, South Africa, India and South America. Among the South American specimens there are basal Squamata forms (Olindalacerta and Tijubina) and a possible iguanid (Pristiguana) form Brazil. In Argentina gondwanian terrestrial lizards are represented by a putative iguanid and a small, poorly preserved dentary. This last specimen, recovered from the Anacleto Formation (Neuquén Group, Río Colorado Subgroup) in vicinity of the locality of Cinco Saltos (Río Negro Province), is here described formally. Comparisons with extant lizards indicate more affinity of the fossil with the Scincomorpha (non Scincophidia) than with any other group of lizards. This finding suggests that lizards were probably better represented and more diverse in the Mesozoic of South America than previously thought, although the fossil record is, at the moment, much poorer than in Laurasia. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Squamata Lizards Scincomorpha Cretaceous Patagonia
1. Introduction Extant squamates (Squamata) constitute a successful group of reptiles that, according to osteological-based phylogenetic hypothesis (contra molecular-based ones e.g. Vidal and Hedges, 2009; see Conrad, 2008 and references therein), includes two main clades, the Iguania and the Scleroglossa (Iguanomorpha and Scincogekkonomorpha if fossils are considered). Although lizards (non-amphisbaenian, non-serpentian squamates) constitute the majority of the living squamates, they are not a monophyletic group (e.g. Estes et al., 1988; Conrad, 2008; Vidal and Hedges, 2009). Lizards natural history is ancient but little known, especially in gondwanian territories (Evans, 2003). In South America the lizard fossil record is limited to a few findings in the Cretaceous of Brazil and Argentina (Estes and Price, 1973; Bonfim and Marques, 1997; Evans and Yabumoto, 1998; Albino, 2002, 2007; Apesteguía et al., 2005; de la Fuente et al., 2007; Candeiro et al., 2009). The Neuquén Group is one of the richest sedimentary unit in fossil vertebrates of Patagonia (Leanza et al., 2004). Within the Neuquén Group, the Río Colorado Subgroup (the upper third part of the Neuquén Group) is made up of two Formations: the inferior Bajo de la Carpa Formation and the superior Anacleto Formation (Cazau and Uliana, 1973; Leanza and Hugo, 2001; Leanza et al., 2004) (Fig. 1). This last Formation was deposited between 83.5
* Corresponding author. E-mail addresses: [email protected] (S. Brizuela), [email protected] (A. Albino). 0195-6671/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2011.05.006
and 79.5 Ma ago, during the early Campanian (Dingus et al., 2000). Leanza et al. (2004) list the tetrapod fauna recovered from the Anacleto Formation, which includes titanosaurid, theropod and ornithischian dinosaurs as well as birds (icnites) and at least one mammalian taxon. Very few Squamata have been recovered from the Anacleto Formation; among them, there is the most modern record of the snake Dinilysia patagonica Woodward, 1901 (Albino, 2007). Lizards are represented in this Formation solely by a small, partial dentary recovered near the locality of Cinco Saltos, Río Negro Province (Fig. 1) (Albino, 2002, 2007). Given the poverty of lizard remains in the Mesozoic of Gondwana (Evans, 2003 and references therein), this finding is significant to understand the early evolution of squamates in these territories. Therefore, the aim of this paper is to describe and discuss the taxonomic affinities of this fossil.
2. Materials and methods The dentary was found by Marcos Poblete in the vicinity of the locality of Cinco Saltos, Río Negro Province, Argentina (Fig. 1). Because of the fragility of the fossil it was covered with abundant glue. Latter it was not possible to remove the glue without damaging the fossil given its poor fossilization state. The glue hinders the observation of some of the details of the dentary and prevents the use of electronic microscopy, particularly to analyze apical tooth morphology. The fossil was confronted directly with osteological material from a diverse group of present-day lizards and its systematic
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Fig. 1. Map of fossil site in vicinities of Cinco Saltos city (38 490 S, 68 040 W) (open circle) and stratigraphic column of the Neuquén Group. A) Río Negro province in gray; B) northwester section of Río Negro province (light gray), Neuquén Group outcrops in dark gray (modified from Ardolino et al., 1994); C) generalized stratigraphic column of the Neuquén Group (modified from Leanza et al., 2004). Figure Legend from left to right: National route; Provincial route; railroad; temporary river; paleosols; conglomerates; sandstones; siltstones; siliceous geodes; mudrocks; volcanic ash.
affinities were analyzed taking into account previously published data. Systematic follows Conrad (2008). 3. Systematic paleontology SQUAMATA Oppel, 1811 SCINCOGEKKONOMORPHA Sukhanov, 1961 EVANSAURIA Conrad, 2008 SCLEROGLOSSA Estes et al., 1988 SCINCOMORPHA Camp, 1923 (not Scincophidia) Gen et sp. indet. (Figs. 2 and 3)
3.1. Referred material Incomplete left dentary. The dentary is housed at the Museo Regional de Cinco Saltos (Cinco Saltos locality, Río Negro Province, Argentina) in the section Paleontología de Vertebrados under the acronym MCS-Pv 41. 3.2. Geographic and stratigraphic provenance Outskirts of the locality of Cinco Saltos (38 490 S, 68 040 W), Province of Río Negro, Argentina (Fig. 1). Anacleto Formation (Neuquén Group, Río Colorado Subgroup), early Campanian (Dingus et al., 2000) (Fig. 1). 3.3. Description The fossil corresponds to the middle-posterior part of a robust dentary, of regular size, and a total length of 10.69 mm. Its size is comparable with that of a similar portion of the dentary of an adult Timon lepidus (Daudin, 1802) (previously Lacerta lepida, maximun snout vent length in males ¼ 240 mm, Mateo and Castanet, 1994; figured in Estes et al., 1988: 212). The dentary is labially plane,
smooth and bears three mental foramina (inferior alveolar foramina of Gao and Fox, 1996) at a middle height and below the tooth positions (a), (d) and (h) (Fig. 2). The dorsal margin of the dentary is straight, whereas the ventral margin is convex, therefore the dentary is deeper posteriorly. The posterior end of the dentary is not preserved; no articulation facet for the anterolateral process of the coronoid is present on the preserved section of the dentary. Lingually, Meckel’s canal is medially opened. The important ventral development of the subdental shelf, whose maximum is achieved the midpoint of the conserved dental series, confines the anterior part of Meckel’s canal. Posteriorly, the subdental shelf tapers, not developing posterior to the (i) tooth position. Ventral on the subdental shelf the articulation facet of the splenial is poorly preserved, extending anteriorly to the (e) tooth position. The ventral border of the subdental shelf and that of the dentary are parallel and closed together in the anterior part of the conserved dentary. Ventral to the (i) tooth position, upon the roof of Mekel’s canal, is the internal foramen of internal mental canal (inferior alveolar canal of Gao and Fox, 1996). Tough cover by glue, there is no apparent posterior projection of the intramandibular septum (i.e. no intramandibular lamella, Smith, 2009). Dorsally on the dentary, developed upon the dental groove is the dental series. Between the bases of the teeth and the moderate subdental ridge of the subdental shelf there is a narrow space which is considered a shallow subdental gutter (i.e. sulcus dentalis). Though tooth bases cannot be adequately observed because of sediment and glue, tooth implantation is considered pleurodont since teeth have at least half their height attached to the labial parapet of the dental groove (pleurodoncy sensu Gao and Fox, 1996). Only 11 tooth positions are preserved, representing the posterior dentition. Teeth (a), (c) and (e) are missing, and only the base of tooth (b) is preserved. Among the remaining teeth, only (g), (h) and (i) are well-preserved. The last tooth (k) is broken, not preserving its distal half. Teeth are robust, firmly attached to the dentary. They are closely spaced and all of the same height, forming a close palisade. The bases of the teeth present a slight mesodistal compression and labiolingual development. The labial faces of the teeth are straight, vertical, whereas
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Fig. 2. Scincomorpha indet. (MSC-Pv 41) from the Anacleto Formation (Campanian) in the outskirts of Cinco Saltos city (Río Negro Province, Argentina). AeC, photograph in (A) labial, (B) lingual and (C) oclusal views. DeF, illustrations in (A) labial, (B) lingual and (C) oclusal views. Abbreviations: a.f.S, articulation facet for the splenial; M.c, Meckel’s canal; m.f, mental foramen; r.p, resorption pit; sb.s, subdental shelf; s.d, sulcus dentalis. Scale 5 mm.
the lingual faces are more oblique. Apically teeth are blunt, with a slight labialelingual compression. Detailed observation of tooth tips is not possible due to conservation and preparation factors. Nonetheless, teeth are unicuspid, with a convex apical outline (Fig. 3). No striae are observed. On the base of tooth (h) there is an important resorption pit which resembles the “iguanid replacement” of Edmund (1969). 4. Discussion
Fig. 3. Apical end of teeth (h) and (i) of fossil MCS-Pv 41. Scale 1 mm.
Albino (2002) first noted this fossil from the Anacleto Formation, tentatively relating it to the Teiidae (Scincomorpha). Latter, she considers that the fossil presents affinities with Pristiguana brasiliensis Estes and Price 1973 (Albino, 2007; de la Fuente et al., 2007), a lizard with Iguania or Teiidae affinities from the Cretaceous of Brazil (Estes and Price, 1973; Borsuk Bialynicka and Moody, 1984). The characters that the dentary from Anacleto Formation
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(MSC-Pv 41) shares with P. brasiliensis are: an anteriorly restricted intramandibular septum, a shallow subdental gutter, and the homodoncy where teeth are attached to the dentary with at least half their height. However, the fossil dentary differs from Pristiguana in not having clearly differentiated cusps on the teeth, whereas Pristiguana has a bluntly tricuspid condition (Estes and Price, 1973). Another difference between these fossils is that in the dentary MCS-Pv 41 Meckel’s canal closes more abruptly than in Pristiguana. Only 12 characters (C170, C171, C181, C182, C188, C211, C213, C214, C217, C219, C221, C225), a 2.3% of those presented by Conrad (2008), could be without doubt scored for fossil MSC-Pv-41. When Conrad’s (2008) data matrix þ MSC-Pv 41 was run in TNT (Goloboff et al., 2008), using the ratchet option set to find the shortest tree 1000 times, saving to RAM and performing two more ratchet analysis on the saved trees (initial part of Conrad’s (2008) protocol), MCS-Pv 41 appeared in a very large basal polytomy in the Strict Consensus (of 10 equally most parsimonic trees, length 3329). Therefore a more traditional character discussion is followed. Dentary MCS-Pv 41 presents a well-developed subdental shelf, a scleroglossan synapomorphy according to Estes et al. (1988). Following Conrad (2008) a subdental shelf is absent in Acrodonta and the scleroglossan Amphisbaenia and Serpentes. Within the Scleroglossa, the “iguanian tooth replacement” of the fossil dentary is indicating more affinity with the Scincomorpha (although not with Scinciformes: Conrad, 2008) than with the Anguimorpha (Edmund, 1969; Conrad, 2008). In this same regard, the intramandibular septum, which is here considered to be found anterior to the midpoint of the articulation of the splenial-angular and the last tooth preserved, is not found within the Anguimorpha. Anguimorpha and the Contogeniidae (Cenomanian-middle Paleocene Scincomorpha) are characterized by a well-developed intramandibular septum, with an important posterior development (Estes et al., 1988; Lee and Scanlon, 2001; Nydam and Fitzpatrick, 2009). This last condition is absent in the fossil specimen. Meckel’s canal of the fossil dentary is medially open, but it is quickly restricted anterior to the internal foramen of internal mental canal. A medially open Meckel’s canal differs from the close condition observed uniformly within the Gekkota and Xantusiidae, and in some species of other families (Estes et al., 1988; Conrad, 2008), like in the majority of the Gymnophthalmidae (Presch, 1980). Meckel’s canal of the studied fossil also differs from that of the Lacertidae and Teiidae where the canal is widely opened all along its extension. The restriction noted by Denton and O’Neill (1995) in the Teiinae Teiidae is more anteriorly restricted. Within the Scincoidea sensu Estes et al. (1988) (i.e. Cordylidae and Scincidae sensu lato) there is an important variation of this character, where Meckel’s canal can be alternatively closed, open or very restricted (Estes et al., 1988). According to Conrad (2008), only in Scelotidae and Scincidae among the Scincidae sensu lato, Meckel’s canal is partially closed as in the fossil dentary, while in Acontidae and Feylinidae (i.e. members of the Scincophidia) it is closed and fused. Tooth morphology varies greatly among Scincomorpha (sensu Estes et al., 1988) at specific and interspecific levels. One can (arbitrarily) distinguish three main basic tooth plans, where exceptions are common. One (1) in which the striae dominantes (see Richter, 1994) form a secondary lingual cusp, common amongst Mesozoic Paramacellodidae and most of the recent Gerrhosauridae and Cordylidae sensu stricto (Kosma, 2004). In an other plan (2), the secondary lingual cusp is formed by different system of cutting edges (cristae linguales) (particularly abundant in Scincidae sensu lato) (Kosma, 2004). In both of these cases the enamel presents distinct dominant striae, a plesiomorphic character of the Scincomorpha or possibly the Scleroglossa (Nydam and Fitzpatrick, 2009). The third type (3) is that present in the Lacertoidea where there are
Fig. 4. Midsection of the left hemimandible of Mabuya frenata (Universidad Nacional de Mar del Plata 1599). Abbreviations: aiaf, anterior interior alveolar foramen; sb.s, subdental shelf; Sp, splenial. Scale 2 mm.
no marked, distinct main striae (e.g. striae dominantes or cristae linguales), enamel is generally smooth (exceptions occur e.g. posterior teeth of adult Tupinambis) and cusp are meso-lingualy orientated (exceptions occur in some extant Teiinae Teiidae, e.g. Teius and Dicrodon, and in some Borioteiioidea, e.g. Dicothodon). Fossil MCS-Pv 41 does not fall clearly in any of these types. Teeth with a blunt apical outline differ from those present in the majority of Lacertoidea which have acute tooth tips with several cusps (Presch, 1974; Herrel et al., 2004). Moreover, their distribution forming a palisade of closely together teeth of same height differs from the condition observed in the most Teiioidea where teeth are spaced and not always of the same height. A similar tooth disposition as that of the fossil was observed in the present-day genus Mabuya (Scincidae), although in this genus teeth are somewhat more spaced (Fig. 4). The teeth of the fossil and Mabuya share blunt distal outlines, although the teeth of Mabuya present a more complex apical morphology (bicuspid teeth, with cristae lingualis). In light of the stated above, specially taking into account the abrupt anterior restriction of Meckel’s canal, the teeth in palisade, with a blunt distal outlines and laterally compressed, the fossil can be tentatively assigned to the Scincomorpha not Scincophidia. Among the extant representatives of the Scincomorpha the fossil further differs from the Xantusiidae (open Meckel’s canal) and Lacertidae (in basic tooth morphology and disposition). The fossil cannot be differentiated from Cordyliformes (Cordylidae sensu stricto and Gerrhosauridae), Scelotidae nor Scincidae. Yet tooth morphology differs from the general tooth plan observed in these taxa (see above). These lizard families closely resemble the Scincoidae of Estes et al. (1988), with the exclusion of Acontidae and Feylinidae of Conrad (2008). Estes et al. (1988) based their differentiation of families Scincidae sensu lato, Cordylidae and Gerrhosauridae on cranial and postcranial characters not conserved in the fossil. Furthermore it has been stated that it is difficult to distinguish them based on dentary characters alone (Krause et al., 2003). A straight ventral margin of the dentary (not observed in the fossil) is considered by some authors as indicative of Cordylidae affinities although this character is present in some Scincidae sensu lato (Krause et al., 2003). Therefore, the fossil cannot be evaluated at a lower taxonomic level. Compared with Konkasaurus mahalana Krause et al., 2003, the only other known Scincomorpha non-Scincophidia gondwanian taxon, MCS-Pv 41 is deeper and a presents simpler tooth morphology. 5. Conclusions The continental lizards of the Mesozoic of South America are represented by few records. The lower and middle Jurassic reference of lizards in Patagonia (Casamiquela, 1962, 1975, 1980; Rauhut et al., 2001; Rauhut and Puerta, 2001; Evans, 2003) and lower
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Cretaceous of northwest Argentina (Huene, 1931) are dismissed (Estes, 1983; Albino, 2007). Likewise, the report of a possible teiid in the Cretaceous of Chile (Gayet et al., 1992; Albino, 1996) has never been confirmed (Albino, 2007). Furthermore many of the possible teiid and iguanian remains from the late Cretaceous of Patagonia (Leanza et al., 2004; Albino, 2007) are not fossils. The most complete lizard specimens are those of the early-middle Cretaceous (AptianeAlbian) (Olindalacerta brasiliensis and Tijubina pontei) and late Cretaceous (Maastrichtian) (Pristiguana brasilensis) of Brazil, the former being basal forms of squamates of uncertain phylogenetic relationships (Estes and Price, 1973; Bonfim and Marques, 1997; Evans and Yabumoto, 1998), the latter a possible Iguanid or Teiidae (Estes and Price, 1973; Borsuk Bialynicka and Moody, 1984). A partial skeleton of an indeterminate non-serpentian squamate has also been recovered from the Maastrichtian of Brazil (Candeiro et al., 2009). In Argentina, the only other Mesozoic lizard fossil is a partial frontal from the Cenomanian assigned to the “Iguanidae” (Apesteguía et al., 2005). Consequently, the dentary from the Anacleto Formation described in this paper constitutes the first record of a Scincogekkonomorpha lizard in the Cretaceous of South America. The tentative assignation to the Scincomorpha nonScincophidia allows to hypothetize that the group was already present in gondwanian territories in the late Cretaceous. The presence of a probable Cordylidae in the Maastrichtian of Madagascar (Krause et al., 2003) supports this hypothesis. This finding suggests that the presence of lizards in the Mesozoic of South America is sub-evaluated because its fossil record is composed of small, very fragmentary elements which are of poor preservation, and have not been intentionally targeted in the different fossil bearing sites of South America. Acknowledgments We like to thank Leonardo Salgado who notices us about the fossil specimen described in this paper and Ignacio Cerda for facilitating the studied material. We also thank reviewers S. Apesteguía and M.E.H. Jones as well as Editor M.B. Hart for their comments and suggestions on the early version of this contribution. PIP-CONICET 112-200901-00176 financed this study. References Albino, A.M., 1996. The South American Fossil Squamata (Reptilia: Lepidosauria). In: Arratia, G. (Ed.), Contributions of Southern South America to Vertebrate Paleontology (A)30. Münchner Geowissenchaftliche Abhandlungen, München, pp. 185e202. Albino, A.M., 2002. El lagarto más antiguo de la Argentina. I Congreso “Osvaldo A. Reig” de Vertebradología básica y evolutiva e Historia y Filosofía de la Ciencia, Bs. As., 2002, p. 21. Albino, A.M., 2007. Lepidosauromorpha. In: Gasparini, Z., Salgado, L., Coria, R.A. (Eds.), Patagonian Mesozoic Reptiles. Indiana University Press, Bloomington, Indiana, pp. 87e115. Apesteguía, S., Agnolin, F.L., Lio, G.L., 2005. An early Late Cretaceous lizard from Patagonia, Argentina. Comptes Rendus Palevol 4, 311e315. Ardolino, A., Caminos, R., Chucci, R., Franchi, M., Leanza, H., Lizuain, A., Nullo, F., 1994. Mapa geológico de la provincia de Río Negro, República Argentina. Bonfim Jr., F., Marques, R.B., 1997. Um novo lagarto do Cretáceo do Brazil (Lepidosauria, Squamata, Lacertilia e Formaçao Santana, Aptiano da Bacia do Araripe). Anuário do Instituto de Geociencias 20, 233e240. Borsuk Bialynicka, M., Moody, S.M., 1984. Priscagaminae, a new subfamily of the Agamidae (Sauria) from the Late Cretaceous of the Gobi Desert. Palaeontologia Polonica 29, 51e81. Candeiro, C.R.A., Navas, C.A., Martinelli, A.G., Forasiepi, A.M., Scanferla, C.A., Muzzopappa, P., 2009. New lizard record (Diapsida, Lepidosauria) from the Upper Cretaceous Adamantina Formation, Brazil. Bulletin of Geosciences 84, 573e576. Casamiquela, R.M., 1962. Sobre la pisada de un presunto sauria aberrante en el Liásico del Neuquén (Patagonia). Ameghiniana 2, 183e186. Casamiquela, R.M., 1975. La presencia de un sauria (Lacertilia) en el Liásico de Patagonia austral. I Congreso Argentino de Paleontología y Bioestratigrafía, Actas, 57e70.
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