Cretaceous floras containing angiosperm flowers and fruits from eastern North America

REvdEw

PAlAEU&6oTANY Review of Palaeobotany and Palynology 90 (1996) 319-337

PALYNOLOGY

Cretaceous floras containing angiosperm flowers and fruits from eastern North America Peter R. Crane, Patrick S. Herendeen Department of Geology, The Field Museum, Roosevelt Road at Lake Shore Drive, Chicago, IL 60605, USA

Received 10 November 1994; revised and accepted 20 January 1995

Abstract A recent innovation in paleobotanical studies of the Cretaceous has been the use of bulk sediment d&aggregation and sieving techniques. This approach has identified numerous Cretaceous floras that contain well-preserved plant fossil debris (“mesofloras”), and many of these have yielded abundant fossil angiosperm flowers, as well as angiosperm fruits, seeds and dispersed stamens. 0x1 the Atlantic Coastal Plain of eastern North America recent research has identified a new series of fossil floras of Campanian age from central Georgia. These form part of a rich sequence of mesofloras that range in age from early Aptian (or perhaps late Barremian) to Campanian. Detailed studies of fossil flowers from these floras have clarified the systematic relationships of Cretaceous angiosperms and identified source plants of several characteristic dispersed angiosperm pollen grains. Taxa referable to extant angiosperm families appear suddenly in the Albian and Cenomanian, and the number of extant angiosperm families that can be recognized increases rapidly through the Late Cretaceous. Based on the record of Cretaceous fossil flowers, “modernization” of angiosperm lineages occurred much earlier than had been inferred previously from studies of dispersed fossil pollen. Major extinct monophyletic “higher” taxa of Cretaceous angiosperms have not yet been recognized.

1. Introduction

The paleobotanical record documents a massive and coordinated increase in the diversity and abundance of angiosperm pollen and leaves that begins in the Early Cretaceous (c. 130 Ma) and continues into the Tertiary (Doyle and Hickey, 1976; Hughes, 1976; Hickey and Doyle, 1977; Lidgard and Crane, 1988, 1990; Crane and Lidgard, 1989, 1990). Until recently (e.g. Dilcher, 1979) information on Cretaceous angiosperms was confined almost entirely to leaf, wood and pollen remains, and flowers were virtually unknown. However, in the last 15 years there has been a spectacular increase in knowledge of Cretaceous angiosperm reproductive structures, mainly through the application 0034-6667/96/$15.00 0 1996Elsevier Science.B.V. All rights reserved SSDI 0034-6667(95)00090-9

of bulk sieving methods to unconsolidated sediments (e.g. Friis and Skarby, 1982). These techniques have yielded large numbers of exquisitely preserved flowers, fruits and other fossils from assemblages of dispersed plant debris (“mesofossils”). The material may be lignified or preserved as fusain (fossil charcoal), but both modes of preservation retain a wealth of structural details. Studies of these fossils have clarified the systematic relationships of many Cretaceous angiosperms, identified the plants that produced many distinctive Cretaceous pollen grains, and yielded important new information from which the reproductive biology of Cretaceous flowering plants can be inferred (e.g. Friis and Skarby, 1982; Friis, 1983; Friis et al., 1986, 1988; Crane et al., 1989).

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Cretaceous angiosperm flowers or flower parts are now known from several continents, but the majority of studies have been conducted in Europe and North America. On the Atlantic Coastal Plain of eastern North America alone, more than twenty separate localities ranging in age from early Aptian (or perhaps late Barremian) through Campanian have yielded well-preserved angiosperm flowers. These fossils complement inferences on early angiosperm evolution based on pollen and leaf macrofossils and have substantially expanded previous knowledge of angiosperm evolution. In this paper we introduce preliminary results from a new locality in central Georgia, provide a brief overview of recent studies on angiosperm reproductive structures from the Cretaceous of eastern North America, and discuss the implications of this record for interpreting the pattern of Cretaceous angiosperm diversification.

2. Selected Cretaceous floras on the Atlantic coastal Plain The Atlantic Coastal Plain of eastern North America preserves a remarkable series of Cretaceous mesofloras that contain rich assemblages of angiosperm flowers and other reproductive structures. Geographically these floras extend from Martha’s Vineyard in the north to central Georgia in the south, and occur in unconsolidated deposits that reflect a variety of continental depositional settings. In general, exposures at these localities are poor and few detailed sedimentological and paleoecological studies have been undertaken. Stratigraphically, the precise age of many floras on the Atlantic Coastal Plain is poorly constrained by non-paleobotanical criteria, and age determinations have frequently been based on correlation of palynofloras with pollen and spore assemblages elsewhere for which there is some independent age control. The approximate age relations of key floras with fossil angiosperm flowers and fruits are summarized in Fig. 1. In the following review we consider these floras under four headings: Early Cretaceous (early-middle Aptian), late Early Cretaceous (late Aptian-early (late Albian-early Albian) , mid-Cretaceous

Cenomanian) , and Late Cretaceous

(Turonian-

Campanian) . 2.1. Early Cretaceousfloras

(early-middle Aptian)

The oldest Cretaceous floras identified so far from the Atlantic Coastal Plain are from the Potomac Group of Maryland and Virginia. These floras (e.g. Dutch Gap, Drewry’s Bluff) have been assigned to Zone I in the palynological zonation established for Potomac Group sediments by Brenner (1963), Doyle (1969), Doyle and Robbins (1977) and others. Lower Zone I floras (e.g. Dutch Gap, Drewry’s Bluff clay balls) were originally thought to be of probable Barremian age (Doyle and Robbins, 1977), but more recent studies suggest that lower Zone I floras are probably early Aptian, based on correlations to low-latitude Early Cretaceous sequences (Doyle, 1992). Upper Zone I floras (e.g. Drewry’s Bluff leaf bed) were originally dated as early Aptian (Doyle and Robbins, 1977) but are now interpreted as of middle Aptian age (Doyle, 1992). Palynofloras from Zone I localities consist almost entirely of pteridophyte spores and gymnosperm pollen (Doyle and Hickey, 1976; Hickey and Doyle, 1977). In a palynological sample from Dutch fern spores, Classopollis, Gap, Exesipollenites turn&s, Inaperturopollenites dubius

and bisaccate pollen grains each account for between 15 and 20% of the palynoflora (Upchurch and Doyle, 1981). In a palynological sample from clay balls at Drewry’s Bluff, Classopollis and Exesipollenites grains account for 78 and 10.5% respectively. In both samples the abundance of angiosperm grains (excluding equivocal smooth monosulcates) was less than 1% (Upchurch and Doyle, 1981). The majority of angiosperm pollen grains in Zone I are monosulcate forms (e.g. Clavatipollenites, Brenneripollis, Stellatopollis) that are attributable

Liliacidites,

to magnoliid dicots or perhaps basal monocots. Tricolpate pollen diagnostic of eudicots was originally thought to be restricted to upper Zone I but is now known to occur rarely at lower Zone I localities (Doyle, 1992). The occurrence of angiosperm macrofossils at

p.R Crane, P.S. Herenaken/ReviewofPalaeobotanyand PaIynology90 (i996) 319-337

vlaastrichtiar

Zampanian

Martha’s Vineyard (Massachusetts) Allon (Georgia) Whitewater Creek (Georgia) Neuse River (North Carolina)

Santonian

Upatoi Creek (Georgia)

Zoniacian Turonian

Crossman (New Jersey)

Zenomanian Mauldin Mountain (Maryland) Bull Mountain (Maryland)

Albian

West Brothers (Maryland), Quantico (Virginia)

Bank near Brooke (Virginia), Puddledock (Virginia)

Aptian

Drewry’s Bluff leaf bed (Virginia) Dutch Gap (Virginia), Drewry’s Bluff clay balls (Virginia

Barremian

Hauterivian Valanginian Berriasian Fig. 1. The approximate age relations (million years before present) of key floras from eastern North America.

321

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Zone I localities is even more sporadic than the occurrence of angiosperm pollen. About 12 leaf types have been recognized, most of which are of probable magnoliid affinity (Rogers& perhaps two taxa with Ficophyllum) (Acaciaephyllum, Plantaginopsis) representing early monocotyledons (Hickey and Doyle, 1977; Upchurch, 1984). Upchurch also recorded dispersed angiosperm leaf cuticles from both lower and upper Zone I localities (Upchurch, 1984). The best preserved suite of Zone I macrofossils is from the Drewry’s Bluff leaf bed (Upchurch, 1984). In this flora fragments of fern fronds, angiosperm leaves and shoots of the probable gnetalean Drewriupotomacensis are the most common fossils, with conifer shoots and cycadophyte leaves as subordinate elements. The diversity (five taxa) and abundance of angiosperm leaves in the Drewry’s Bluff leaf bed is unusual compared to other Zone I macrofossil localities where fern, conifer, cycad and bennettitalean remains predominate (e.g. Schizaeaceae, Pseudofrenelopsis, Podozamites, Taxodiaceae, Zamites). The unusual composition of the Drewry’s Bluff flora may reflect the preservation of herbaceous to shrubby early successional vegetation (Crane and Upchurch, 1987). Despite the availability of well-preserved mesofossil assemblages from Zone I of the Potomac Group no unequivocal angiosperm remains have so far been identified. The gymnospermous mesofossils that have been described in detail include seeds with Eucommiidites pollen in the micropyle (Brenner, 1967), and microsporangiate structures yielding Decussosporites pollen, and seeds containing Decussosporites in the micropyle (Pedersen, Friis and Crane, 1993), both from Drewry’s Bluff clay balls. 2.2. Late Early Cretaceousjoras

(early-middle

Albian; Table 1)

In eastern North America early or middle Albian fossil floras are currently known only from the Potomac Group. Among the floras of this age considered by Doyle and Hickey (1976) and others (Hickey and Doyle, 1977; Upchurch, 1984; Upchurch et al., 1994), those that have been most intensively investigated are West Brothers,

319-337

Quantico, and Bank near Brooke. In addition, an important new group of mesofossil floras (Puddledock) has been discovered that contains especially diverse angiosperm remains (Crane et al., 1994; Friis et al., 1994a, 1995). These floras can be assigned to palynological Subzone IIB, originally considered by Doyle and Robbins ( 1977) to range from the middle to upper Albian. Recent reevaluation (Doyle, 1992) suggests that floras from lower Subzone IIB may be as old as early Albian, while floras from upper Subzone IIB may be of middle Albian age. Floras attributable to lower Subzone IIB include Bank near Brooke and Puddledock. At Bank near Brooke the macrofossil flora is dominated by pinnatifid Supbuiopsis foliage (Fontaine, 1889; Doyle and Hickey, 1976; Hickey and Doyle, 1977) that has been linked to pistillate inflorescences (Platanocarpus brookensis) and staminate inilorescences (Aquiu brookensis) (Crane et al., 1993). Evaluation of the systematic aflinities of the reconstructed fossil plant indicates that it is attributable to the lineage that includes extant Platanus (Crane et al., 1993). Macrofossils at the Bank near Brooke locality also include trochodendroid and other angiosperm leaves, as well as conifer shoots, leaves and pollen cones, and fragmentary fern foliage. Cycad or bennettitalean foliage has not been recovered during our collecting from the Bank near Brooke locality. At the Puddledock locality the large number of exquisitely preserved mesofossil floras differ substantially in composition but all contain diverse and abundant assemblages of plant remains in which angiosperms, together with various conifers, such as Pseudofrenelopsis, Glenrosa virginiensis and undetermined taxodiaceous shoots (Srinivasan, 1992), dominate the fossil assemblages. A possible liverwort is common in some assemblages, and pteridophytes are represented by Onychiopsis (Dicksoniaceae), schizaeaceous ferns, dispersed sporangia, and various smooth and reticulate megaspores. Unequivocal cycads or Bennettitales have not been encountered, although a variety of enigmatic gymnosperm remains are present. The angiosperm component of the Puddledock mesofossil assemblages includes a range of magnoliids, some of which show clear relationships or

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Crane, P.S. HerendeenfReview of Palaeobotany and Palynology 90 (1996) 319-337

Table 1 Selected published records of angiosperm North America

323

reproductive structures from late Early Cretaceous floras (early-middle Albian) in eastern

Taxon/material

Plant part

Systematic relationship

Age

References

Conical magnolialean gynoecium

Gynoecium

Magnoliales

Crane et al. (1994a)

Bisexual, hypogynous flower

Flower

Magnoliidae

Stamens (at least four types)

Stamen

Magnoliidae

Lauralean flower and stamen

Flower and stamen

Laurales

Unilocular one-seeded fruit

Fruit

Magnoliidae, close to Laurales or Piperales

Virginianthus calycanthoides

Flower

Chloranthoid androecium

Androecium of three stamens

Similar to Calycanthaceae (including Idiospermum) Probably Chloranthaceae

Appomatoxia ancistrophora

Fruit

Similarities to

Early-middle Albian (Puddledock, Potomac Group) Early-middle Albian (Puddledock, Potomac Group) Early-middle Albian (Puddledock, Potomac Group) Early-middle Albian (Puddledock, Potomac Group) Early-middle Albiin (Puddledock, Potomac Group) Early-middle Albian (Puddledock, Potomac Group) Late Albian (West Brothers, Potomac Group) Early-middle Albian (Puddledock, Potomac Group) Late Albian (West Brothers, Potomac Group) Late Albian (Quantico, Potomac Group)

Drinnan et al. (1991)

Circaeaster,

Chloranthaceae, and Piperales Buxaceae

Crane et al. (1994a)

Crane et al. (1994a)

Crane et al. (1994a)

Crane et al. (1994a)

Friis et al. (1994a)

Crane et al. (1989)

Friis et al. (1995)

Spanomera marylandensis

Staminate flower and fruits

Reproductive structures associated with

Tepals, fruiting receptacle and fruits

Probably Nehnnbonaceae

Nehonbites extenuinervis Platanocarpus brookensis, Aquia brookensis, Sapindopsis

Staminate and pistillate inflorescences and infructescences

Platanaceae

Early-middle Albian (bank near Brooke, Potomac Group)

Crane et al. (1993)

Platanocarpus marylandensis, Platananthus potomacensis

Staminate and pistillate intlorescences

Platanaceae

Late Albian (West Brothers, Potomac Group)

Friis et al. (1988)

Staminate flower with five stamens

Flower

unknown

Albian Potomac

Crane et al. (1994a)

Pistillate flower with five carpels

Flower

Unknown

Albian Potomac

Crane et al. (1994a)

Epigynous flowers (at least two types)

Flower

Unknown

Early-middle (Puddledock, Group) Early-middle (Puddledock, Group) Early-middle (Puddledock, Group)

Albian Potomac

Crane et al. (1994a)

Upchurch et al. (1994)

SP.

324

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similarities to modern groups, for example, Calycanthaceae (Virginianthus calycanthoides), and perhaps Chloranthaceae Laurales, Magnoliales and Piperales (Appomattoxia ancistrophoru) (Crane et al., 1994; Friis et al., 1994a, 1995). Unequivocal monocotyledons have not yet been identified. Eudicots include dispersed probable platanoid fruits and stamens, as well as several other fruit and stamen types. The macrofossil flora from the Quantico locality has recently been monographed by Upchurch et al. (1994) who document 22 species of leaves and shoots, including nine species of conifers and 12 species of angiosperms. Pteridophytes and cycadophytes are both represented by a single species each. The angiosperm component of the flora includes five probable magnoliids and three species attributable to the platanoid-Supindopsis complex (Upchurch et al., 1994). The heavily oxidized condition of the sediments at the Quantico site precludes recovery of a palynoflora or mesoflora. At the West Brothers locality the palynological assemblage is dominated by angiosperm pollen (Brermer, 1963; Doyle, 1969; Doyle et al., 1975; Doyle and Hickey, 1976). Brenner (1963) records that the palynoflora is approximately 30% fern spores, 15% conifer pollen, and 45% angiosperm pollen. The macrofossil assemblage at West Brothers is dominated by pinnate or pimratifid Supindopsis foliage and pahnately lobed platanoids (Friis et al., 1988), both of which are probably attributable to the platanoid lineage (Crane et al., 1993). Other macrofossils include fragmentary angiosperm leaves and conifer shoots. The presence of platanoids in the macroflora is also reflected in the mesoflora, where platanoid staminate inflorescences, stamens (Platananthus potomucensis) and pistillate inflorescences (Platanocurpus marylandensis) are common (Friis et al., 1988). Probable platanoid wood (Icucinoxylon sp.) is also present (Herendeen, 1991b). Other angiosperms present in the West Brothers mesoflora include a probable chloranthoid androecium (Friis, Crane and Pedersen, 1986; Crane et al., 1989), probable buxaceous staminate and pistillate flowers (Spunomera marylundensis; Drinnan et al., 199 1), and dispersed wood (Parczphyllanthoxylon) with affinities to the Lauraceae (Herendeen, 1991a).

These remains, together with a variety of other angiosperm stamens, fruits, and seeds, indicate much greater angiosperm diversity than is indicated by macrofossils. Conifers are represented in the West Brothers mesoflora by shoots, leaves, cone fragments, and seeds. Pteridophytes are represented by megaspores and groups of sporangia. Unequivocal cycads or Bennettitales have not been recovered. 2.3. Mid-Cretaceousflorus

(lute Albian-early

Cenomaniun; Table 2)

Mid-Cretaceous floras here are taken to include fossil assemblages interpreted to be of probable late Album-early Cenomanian age. The Bull Mountain locality in northern Maryland was assigned to palynological Subzone IIC (Doyle and Hickey, 1976; Hickey and Doyle, 1977), which is interpreted as of probable latest Albian age. The Mauldin Mountain locality has been assigned to palynological Zone III (J.A. Doyle, pers. commun.), which is interpreted as of probable latest Albian-earliest Cenomanian age (Doyle and Robbins, 1977). The macroflora at the Bull Mountain locality is dominated by the trilobed platanoid leaves of Araliopsoides cretacea (Newberry) Berry, and macroscopic platanoid reproductive structures have also been recovered (Pedersen et al., 1994). In the mesoflora platanoid staminate (Hamutia elkneckensis) and pistillate material (Platunocarpus elkneckensis) also predominates (Pedersen et al., 1994). Probable platanoid wood (Icucinoxylon sp.) is also present (Herendeen, unpubl. data). The mesoflora is as systematically depauperate as the macroflora and only a few other angiosperm remains have been recovered. The palynoflora at the Mauldin Mountain locality is dominated by angiosperm pollen and this is also reflected in the mesoflora, which includes a considerable diversity of angiosperm flowers, fruits, seeds, and wood. Probable taxodiaceous leafy shoots, cone scales, and seeds are also common, together with dispersed megaspores and occasional fern fragments. The angiosperm component of the Mauldin Mountain mesoflora includes several unequivocal

P. R Crane, P.S. Herer&en/Review

Table 2 Selected published records of angiosperm eastern North America Taxon/material

of Palaeobotanyand Palynology 90 (1996) 319-337

reproductive structures from mid-Cretaceous floras (late Albian-early

Plant part

Undescribed seeds

Age

References

Probable Magnoliales

Earliest Cenomanian (Mauldin Mountain, Potomac Group) Earliest Cenomanian (Mauldin Mountain, Potomac Group) Earliest Cenomanian (Mauldin Mountain, Potomac Group) Earliest Cenomanian (Mauldin Mountain, Potomac Group) Earliest Cenomanian (Mauldii Mountain, Potomac Group) Latest Albian (Bull Mountain, Potomac Group) Earliest Cenomanian (Mauldm Mountain, Potomac Group) Earliest Cenomanian (Mauldin Mountain, Potomac Group) Earliest Cenomanian (Mauldin Mountain, Potomac Group) Earliest Cenomanian (Mauldin Mountain, Potomac Group)

Plate I, 5

Staminate flower

Magnoliidae

Couperites mauldinensis

Fruit with

Chloranthaceae

Clavatipollenites pollen

on the stigmatic surface Inflorescence with flowers

Lauraceae

Spanomera mauldinensis

Staminate and pistillate flowers and fruits

Buxaceae

Platanocarpus elkneckensis, Hamatia elkneckensb

Staminate and pistillate inflorescences

Platanaceae

Undescribed stamen

Stamen

Platanaceae

Undescribed stamen

Stamen

Eudicot

Undescribed wedge-shaped unicarpellate fruit Undescribed bicarpellate fruit

Cenornanian) in

Systematic relationship

Undescribed staminate flower

Mauldinia mirabilis

325

Probable eudicot

Eudiwt

Magnoliidae. The Lauraceae are represented by flowers and inflorescences of Mauldinia mirabilis (Plate I, 6; Drinnan et al., 1990), and at this locality Mauldinia has been conclusively linked to marylandense of Paraphyllanthoxylon wood ( Herendeen, 199 1a). Other magnoliids include small unilocular single-seeded fruits (Plate I, 8; Couperites) associated with Clavatipollenites pollen (Plate II, 5; Pedersen et al., 1991) that are probably closely related to Chloranthaceae, and a small inflorescence or staminate flower (Plate I, 7) containing Brenneripollis pollen (Plate II, 6). Also present in the Mauldin Mountain flora are ellipsoidal seeds that adhere laterally into linear groups suggesting the possibility that they developed in a multiseeded follicle (Plate I, 5). These seeds may

have

been

from

Pedersen et al. (1991) Drimran et al. (1990) Drinnan et al. (1991) Pedersen et al. (1994) Plate I, 3

Plate I, 1

Plate I, 2

Plate I, 4

a plant similar to (Dilcher and Crane, 1984), which occurs in sediments of similar age in central Kansas. Possible magnolialean stamens with in situ monosulcate, boat-shaped pollen (Plate II, 4) are also present at Mauldin Mountain (Friis et al., 1991). Eudicots are diverse in the Mauldin Mountain mesofossil assemblage but most appear to be attributable to various “lower” hamamelid groups. Staminate and pistillate material of the probable buxaceous Spanomera mauldinensis are abundant (Drinnan et al., 1991), as are undescribed platanoid remains (e.g. Plate I, 3) and probable platanoid wood attributable to Icacinoxylon (Herendeen, 1991b). Other eudicots in the Archaeanthus

derived

Plate I, 7

linnenbergeri

326

PLATE I

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321

PLATE II

Angiosperm pollen associated with reproductive structures from the Mauldin Mouutain locality (latest Albian+arliest 1. Tricolpate pollen on stigma of bicarpellate fruit (Plate I, 4). PP35035. x 4000. 2. Tricolpate pollen of Spanomera mauidihensis (Drinnan et al., 1991). PP34945. x 3200. 3. Tricolpate pollen from anther figured in Plate I, 1. PP44587. x 3000. 4. Monosulcate pollen from probable magnoliid anther. PP34948. x 2350. 5. Monosulcate pollen of Couperites mauldinensb (Pedersen et al., 1991). PP34957. x 1800. 6. Monosulcate pollen found in anthers figured in Plate I, 7. PP44589. x 4000.

Cenomanian).

PLATE I Angiosperm reproductive structures from the Mauldin Mountain locality (latest Albian-earliest Cenomanian). 1. Dispersed anther with short apical connective extension (see Plate II, 3 for pollen). PP44587. x 36. 2. Unilocular wedge-shaped fruit with sessile stigma and open ventral margin. PP44588. x 50. 3. Dispersed platanoid stamen. PP35127. x 65. 4. Bicarpellate fruit with sessile stigma (see Plate II, 1 for pollen on stigma). PP35035. x 55. 5. Dispersed seeds with probable magnolialean aRnities. PP44608. x 15. 6. Flower of Mauldinia mirabilis (Drinnan et al., 1990). PP35316. x 33. I. Single stamen (from staminate flower or inflorescence) with long apical connective extension (see Plate II, 6 for pollen). PP44589. x 100. 8. Fruit of Couperites mauldinensis (see Plate II, 5 for pollen of Couperites; Pedersen et al., 1991). PP35215. x 80.

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Mauldin Mountain mesoflora include small wedgeshaped fruits resembling those of the extinct latest Cretaceous and Tertiary genus Nordenskioldia (Trochodendraceae) (Plate I, 2), bicarpellate fruits with tricolpate pollen on the stigmatic surface (Plate I, 4; Plate II, l), and a variety of stamen types with tricolpate pollen (Plate I, 1; Plate II, 3). Occasional epigynous rosiid flowers have also been recovered but these await detailed study and are much less common than in later floras (e.g. Allon). 2.4. Late Cretaceousfloras

(Turonian-Campanian;

Table 3) The Late Cretaceous floras considered here include plant fossil assemblages of possible Turonian to Campanian age. Except for a single report of angiosperm flowers from Martha’s Vineyard (Tiffney, 1977) there are three important groups of Late Cretaceous localities on the Atlantic Coastal Plain in New Jersey, North Carolina, and Georgia. Recent studies of a suite of localities from the Crossman clay pit and adjacent sites in the vicinity of Sayreville, New Jersey, have yielded a diverse assemblage of angiosperm fossils (Crepet and Nixon, 1993, 1994a,b; Crepet et al., 1992; Herendeen et al., 1993, 1994; Nixon and Crepet, 1993a,b, 1994). These localities are assigned stratigraphically to the South Amboy Fire Clay Member of the Raritan Formation ( Herendeen et al., 1994). Based on palynological analyses the South Amboy Fire Clay has been assigned to the Complexiopollis exigua-Santalacites minor palynozone, which is considered to be of middle-late Turonian age (Christopher, 1979). The South Amboy Fire Clay palynoflora is dominated by angiosperm pollen, with tricolporates comprising c. 30%, and Normapolles and triporate types c. 35%, of the pollen assemblage. The Complexiopollis exigua-Santalacites minor palynozone is dominated by species of Complexiopollis, Santalacites minor, and Momipites fragilis (Christopher, 1979). Fossil plant assemblages from the Black Creek Formation, exposed in the “Neuse River Cut-Off” near Goldsboro, North Carolina, were among the first Cretaceous floras to be described with wellpreserved angiosperm flowers (Friis, 1988; Friis

et al., 1988). The plant-bearing sediments are considered to be early Campanian in age (Owens and Sohl, 1989). Several diverse fossil floras have recently been discovered in central and western Georgia, of which the most thoroughly studied is from the Allon Quarry at Gaillard, Georgia (Herendeen et al., 1995). Sediments at the Allon locality have been assigned to the Buffalo Creek Member of the Gaillard Formation (Huddlestun and Hetrick, 199 1) . A single fossil-bearing clay lens interbedded with sands at the Allon locality has yielded wellpreserved dispersed angiosperm flowers and fruits, as well as leaf compressions and a diverse palynoflora (Lupia, 1994). The clay lens at the Allon locality was investigated by Christopher (in Huddlestun and Hetrick, 1991), who assigned the palynological assemblage to the ?Pseudoplicapollis cuneata-Semioculopollis verrucosa assemblage zone, which is considered to be late Santonian to possibly earliest Campanian in age (Christopher, 1979). Like other Late Cretaceous localities, the palynological assemblage is dominated by angiosperms and is particularly rich in Normapolles grains. Other newly discovered Late Cretaceous localities in Georgia include Whitewater Creek and Upatoi Creek (Herendeen, unpublished). Whitewater Creek is approximately 25 km southwest of the Allon locality, with which it shares several taxa. Along Upatoi Creek, in central westem Georgia, a suite of localities is yielding several well-preserved assemblages from the lower part of the Eutaw Formation. These assemblages are somewhat older than those at the Allon and Neuse River sites and are considered to be of Santonian age (Reinhardt and Donovan, 1986). Fossil assemblages from the TuronianCampanian floras of the Atlantic Coastal Plain are dominated by angiosperm remains, especially taxa with triaperturate pollen (eudicots) that are of hamamelid, rosiid, and dilleniid affinity. The spectrum of taxa is very similar to that in the late Santonian-early Campanian assemblages from southern Sweden (e.g. Friis and Skarby, 1982; Friis, 1983, 1984,199O; Friis et al., 1988; Srinivasan and Friis, 1989). Ferns and lycopods are represented by fragmentary remains including leaves and megaspores. Gymnosperms are not diverse,

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329

Table 3 Selected published records of angiosperm reproductive structures from Late Cretaceous floras (Turonian-Maastricht North America

in eastern

Taxon/material

Plant part

Systematic relationship

Age

References

Spirematospermum chandler@

Seed

Zmgiberales

Friis (1988)

Chloranthistemon crossrnanensis Perseanthus crossmanensir

Three-lobed stamen

Cbloranthaceae

Flower

Lauraceae

Undescribed magnolialean flowers (at least two types) Undescribed fruit

Flowers with cupshaped receptacle

Magnoliidae, similar to Eupomatiaceae and Calycanthaceae Similar to Laurales

Santonian- Campanian (Neuse River, Black Creek Formation) Turonian (Crossman, Raritan Formation) Turonian (Crossman, Raritan Formation) Turonian (Crossman, Raritan Formation)

Plate IV, 5

Unnamed flowers

Flower

Allovia decandra

Flower and stamens

Protofagacea allonensis

Dichasia bearing staminate flowers; fruits and cupules Cupule bearing fruits and dispersed fruits

Fagaceae s.1.

Undescribed flower

Flower

Normapolles taxa

Paleoenkianthus sayrevillensis

Flower and fruit

Ericales

Undescribed flower

Flower

Actinidiaceae

Undescribed flower

Flower and fruit

Similar to Saxifragales

Undescribed flower

Flower

Probable Saxifragales

Unnamed flower

Flower

Eudiwt

Undescribed flower

Flower

Eudicot

Undescribed flower and fNit

Flower and fruit

Eudiwt

Undescribed stamen

Stamen

Eudicot

Undescribed flower

Flower

unknown

Early Campanian (Allon, Gaillard Formation) Turonian (Crossman, Raritan Formation) Early Campanian (Allon, Gaillard Formation) Early campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation) Turonian (Crossman, Raritan Formation) Early Campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation) Earliest campanian (Martha’s Vineyard) Early campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation) Early Campanian (Allon, Gaillard Formation)

Undescribed fruit

Fruit

similar to Hamamelidaceae Hamamelidaceae

Fagaceae s.1.

Herendeen et al. (1993) Herendeen et al. (1994) Crepet and Nixon (1994b)

Crepet et al. (1992) Plate III, 7, 8; Magallon-Puebla et al. (in press) Herendeen et al. (1995) Plate III, 6

Plate III, 5

Nixon and Crepet (1993a) Plate III, 2; Keller et al. (in press) Plate III, 9

Plate III, 1

Tiffney (1977) Plate III, 4

Plate IV, l-3

Plate N, 4

Plate N, 6

330

PLATE III

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but conifers are well-represented in both palynofloras and macrofloras. In general, conifers from the Late Cretaceous mesofossil floras of the Atlantic Coastal Plain have not been described in detail and the most thoroughly studied conifer assemblage is from Neuse River (Hueber and Watson, 1988; Raubeson and Gensel, 1991). The enigmatic, Late Cretaceous genus Androvettia (A. carolinensis; Hueber and Watson, 1988; Raubeson and Gensel, 1991), and Brachyphyllum sp., are probably attributable to the Cheirolepidiaceae. Genitzia reichenbachii and Brachyphyllum squamosum are probably attributable to the Araucariaceae. The affinities of Moriconia cyclotoxon are currently unresolved (Raubeson and Gensel, 1991). Among the angiosperms from TuronianCampanian floras, fossils assignable to the magnoliids are relatively sparse, but include forms similar to Calycanthaceae and Eupomatiaceae flowers with strongly concave floral receptacles (Crossman; Crepet and Nixon, 1993, 1994a,b) and Mauldinia (Lauraceae) (Neuse River, Allon; Drinnan et al., 1990; Crane et al., 1994). Lauraceae are also represented by Perseanthus crossmanensis at the Crossman locality (Herendeen et al., 1994). Additional magnoliids at Crossman include Chloranthistemon crossmanensis (Herendeen et al., 1993). Unequivocal monocotyledons are rare in the New Jersey, North Carolina and Georgia floras, but are represented by leaf macrofossils at Allon and fossil seeds assigned to the genus Spirematospermum at Neuse River (Zingiberales; Friis, 1988; see also Rodriguez-de la Rosa and Cevallos-Ferriz, 1994).

319-337

331

The majority of angiosperm floral structures recovered from Turonian-Campanian floras are attributable to the eudicots. “Lower” hamamelids include platanoids (Friis et al., 1988) and Hamamelidaceae (Plate III, 7, 8; Crepet et al., 1992; Magallon-Puebla), but as in the fossil assemblages from southern Sweden, the angiosperm component is dominated by flowers attributable to the rosiid, “higher” hamamelid, and dilleniid complex. Among “higher” hamamelids, unequivocal Fagaceae occur at the Allon locality (Plate III, 3, 6; Herendeen et al., 1995, unpubl. data). In addition, as in the Swedish flora (Skarby, 1968; Friis, 1983), palynological assemblages are especially rich in Normapolles grains, and at the Allon locality these have been associated with several different kinds of epigynous flowers with similarities to Betulaceae and Juglandales (Plate III, 5; Plate V, 1, 4; Crane et al., 1994b). Among the rosiiddilleniid complex, two groups of taxa seem to be especially diverse and common at Allon and Crossman. One group includes epigynous flowers probably related to the Saxifragales sensu lato (Plate III, 1, 6; Crane et al., 1994b, unpubl. data), while another group of flowers is apparently attributable to the Dilleniidae and especially the Ericales sensu lato and Actinidiaceae (Plate III, 2) (Crane et al., 1994b; Nixon and Crepet, 1993a, 1994; Keller et al., in press). To date no unequivocal flowers of the Caryophyllidae (notwithstanding Nixon and Crepe& 1993b, who reported a flower with pantoporate pollen but with other non-caryophyll features) or Asteridae are known from these Upper Cretaceous localities, although many of the numerous angiosperm taxa

PLATE III Angiosperm reproductive structures from the Allon locality (upper Santonian-lower Campanian). _ trimerous flower of probable saxifragalean aknityPP44590. x 35. 1. &xual 2. Bisexual pentamerous flower with probable aEnities to the Actinidiaceae. PP44591. x 60. 3. Staminate flower of Protofagacea allonensis (Herendeen et al., 1995; see Plate V, 5 for pollen). PP44481. x 70. 4. Bisexual pentamerous flower. PP44592. x 25. 5. Bisexual flower similar to Caryanthus. PP44593. x 45. 6. Trigonous fruit probably related to the Normapolles complex and with possible afhnities to the Juglandales/Myricales (cf. Manningia crassa; Friis, 1983). PP44594. x 16. 7. Fragmentary flower of Hamamelidaceae bearing ten stamens. PP44595. x 27. 8. Single dispersed hamamelidaceous stamen comparable to those in Plate III, 7; note long connective extension. PP44596. x 45. 9. Bisexual bicarpellate possible saxifragakan flower with lobed perianth parts and a bilobed epigynous disc (see Plate V, 6 for pollen). PP44597. x 30.

332

P. R Crane, P.S. HerendeenjReview

of Palaeobotany and Palynology 90 (1996) 319-337

PLATE IV

Angiosperm reproductive structures from the Allon locality (upper Santonian-lower Campanian). l-3. “Spindle fruit”. Immature specimen of tricarpelIate fruit formed from an inferior ovary. PP44598. x 12. 1. Apex of fruit showing receptacle and three-lobed stigma (see Plate V, 3 for pollen). PP44599. x 45. 2. Dispersed stamens yielding same type of pollen (Plate V, 3) as found on “spindle fruits”. PP44600. x 45. 3. Dispersed stamen with welldiierentiated fllament and anther. PP44601. x 50. 4. Unidentified fruit with possible atXnities to the Laurales. PP44602. x 20. 5. Unidentitied epigynous flower. PP44603. x 30. 6.

P. R Crane, P.S. HerendeenfReview of Palaeobotany and Palynology 90 (1996) 319-337

PLATE V

~neios~ermDollenassociatedwith reproductive structures from the Allon locality- (upper __ Santonian-lower Camnanian). _ I 1. Ihlokapoiles-typepollengrain from a dispersedanther. PP44604. x 3700. 2. Tricolpate pollen grain from a dispersedanther.PP44605.x 1800. 3. TricolpatePollenfrom stigmaof fruit from PlateIV, 2. PP44599.x 1600. Pollengrainfrom dispersedanther. PP44606.x 1500. 4. Normapolles-type 5. Pollenof Protofagacea allonensis (Herendeen et al., 1995). PP43879. x 3000. 6. Extremely small pollen of epigynous flower illustrated in Plate III, 9. PP44607. x 8000.

Crossman, Upatoi Creek, and Allon remain to be studied in detail.

at

3. Discussion: implications for angiospem~

diversikation Despite uncertainty over the precise age of some of the fossil floras on the Atlantic Coastal Plain, and the current inability to control for taphonomic differences among localities, mesofossil floras from

eastern North America are an exceptional source of detailed information on the structure and biology of early angiosperms. Together with the extensive series of fossil floras from the Cretaceous of Portugal (e.g. Teixeira, 1948, 1950; Friis et al., 1992, 1994b), these assemblages are providing a wealth of new data for interpreting evolutionary patterns through the first half of angiosperm evolutionary history. The major advance achieved through studies of Cretaceous flowers has been increased precision in

334

P.R Crane, P.S. HerendeenfReview of Palaeobotany and Palynology 90 (1996) 319-337

interpreting the systematic relationships of early angiosperms. Frequently it has been possible to demonstrate that well-characterized fossils have the diagnostic features (synapomorphies) of extant taxa, and in situations where the defining characters of extant taxa are unclear, it has generally been possible to provide a crude phenetic indication of the likely systematic position. Taken together, these data have substantially modified previous estimates of the time of differentiation of extant angiosperm families. Syntheses of palynological data (Muller, 1981, 1984) have suggested that most extant angiosperm families differentiated during the latest Cretaceous or early Tertiary, but recent evidence from floral remains indicates that many groups were already distinct in the midCretaceous. Among the factors that may account for this apparent discrepancy, two seem particularly important. First, it is becoming increasingly clear that there are substantial biases against the representation of certain angiosperm groups in the palynological record, both because of poor preservation (e.g. pollen of Lauraceae) and low pollen production or poor dispersal (Lupia, 1994). Second, in many instances the rigorous palynological criteria used for the unequivocal recognition of extant taxa appear to be based on characters that are diagnostic of subgroups within an extant family. In such situations the palynological record provides a conservative estimate of the time of appearance of extant angiosperm groups but will fail to detect early members of a group that may have more generalized palynological features (cf. Protofagacea; Herendeen et al., 1995). Notwithstanding the availability of more precise systematic data in fossil flowers, the overall pattern of angiosperm diversification that emerges from studies of mesofossil floras from eastern North America is consistent with inferences on early angiosperm evolution based on leaf macrofossils and dispersed pollen grains (Brenner, 1961; Doyle, 1969; Doyle and Hickey, 1976; Hickey and Doyle, 1977). In the early-middle Aptian floras of the Potomac Group (e.g. Dutch Gap, Drewry’s Bluff) angiosperm leaves and pollen are of low diversity, and although leaves may be locally common (e.g. Drewry’s Bluff leaf bed), both leaves and pollen are generally rare. Angiosperm flowers, fruits or

seeds have not yet been unequivocally identified from mesofloras of this age on the Atlantic Coastal Plain. Given this sparse early representation, even in floras that are rich in the well-preserved remains of other taxa, the abundance and diversity of angiosperm reproductive structures in Albian floras is striking. It is also remarkable that in these floras there is strong evidence for the differentiation of several extant lineages of magnoliids (e.g. Calycanthaceae, Chloranthaceae, Lauraceae), “lower” hamamelids (e.g. platanoids, trochodendroids) and possibly early rosiids. By the latest Albian-earliest Cenomanian, there is unequivocal evidence of the rosiid-dilleniid-asterid clade, and by the Turonian-Campanian eudicots are extremely diverse. Among the extant groups recognixed to date in Turonian-Campanian or earlier floras from eastern North America are Zingiberales (monocots), Chloranthaceae, Calycanthaceae, Lauraceae, Magnoliaceae (Magnoliidae), and Buxaceae, Ericales, Fagaceae, Hamamelidaceae, Juglandales, “Saxifragales”, and Platanaceae (eudicots). A distinctive feature of the current angiosperm record from the Cretaceous of the Atlantic Coastal Plain is the apparent absence of large extinct monophyletic higher taxa. Together with increasing evidence that many extant lineages differentiated in the fist half of angiosperm history, this suggests a macroevolutionary signature dominated by background extinction, rather than the extinction of large higher-level groups. Ongoing studies of mesofloras from the Atlantic Coastal Plain and elsewhere provide the opportunity for further clarification and ultimately comparison with macroevolutionary patterns in other groups.

Acknowledgements We thank S. Archangelsky, R. Cuneo and T.N. Taylor for the opportunity to attend the VI Congress0 Argentino de Paleontologia y Biostratigrafia in Trelew, 1994, and the invitation to participate in the symposium on “Paleobiology of Fossil Plants: New Insights and Perspectives”. We also thank E.M. Friis and K.R. Pedersen who contributed to much of the research presented

p. R Crane, P. S. HerendeenjReview of Palaeobotany and Palynology 90 (I 9%) 319-337

here, and W.L. Crepet for unpublished information on the Crossman flora. This work was supported in part by National Science Foundation Grants BSR-9020237 to PRC and INT-9007619 to PSH.

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