James D. Gardner

Morphology and Evolution of Turtles

The unquestioned unity of the Chelonia provides a necessary basis for establishing their interrelationships and determining the evolutionary history within the group. On the other hand, the host of uniquely derived features of the oldest known turtles make it extremely difficult to establish their ancestry among more primitive amniotes. This is illustrated by the great diversity of taxa that continue to be proposed as putative sister-taxa of turtles without general acceptance of any. Nearly every major clade of early amniotes from the late Paleozoic and early Mesozoic has been proposed as a possible sister-taxon of turtles, from synapsids to anapsids and diapsids, including pelycosaurs, captorhinomorphs, procolophonids, pareiasaurs, aquatic placodonts and crocodiles, but none possess derived characters that could be synapomorphic with the unique skeletal structure and patterns of development of the chelonian skull, carapace or plastron, which had reached an essentially modern configuration by the Late Triassic. Numerous molecular biologists have attempted to establish the closest sister-group of turtles through analyses of a host of living species, but there is no way for them to preclude turtles from having evolved from one or another of the Paleozoic or early Mesozoic clades that have become extinct without leaving any other living descendants. On the other hand, recent studies of the genetic and molecular aspects of the development of the carapace and plastron imply unique patterns of evolutionary change that cannot be recognized in any of the other amniote lineages, living or dead. This, together with the retention of a skull without temporal fenestration implies a very early divergence from a lineage that probably retained an anapsid skull configuration. This problem may be resolved by more detailed study of the enigmatic genus Eunotosaurus, from the Late Permian of South Africa.

THE FOSSIL SALAMANDER PROAMPHIUMA CRETACEA ESTES (CAUDATA; AMPHIUMIDAE) AND RELATIONSHIPS WITHIN THE AMPHIUMIDAE

Abstract A revised diagnosis and expanded description are presented for the amphiumid salamander Proamphiuma cretacea based on the original topotypic collection of vertebrae and on new atlantes, trunk vertebrae, and caudal vertebrae from the holotype locality. P. cretacea is the type and only species in the genus and is reliably known only from the Bug Creek Anthills (late Maastrichtian or early Paleocene in age), in the Hell Creek Formation, Montana, USA. A referred dentary originally believed to be from the same locality is shown to have come from the upper part (late Paleocene in age) of the Ravenscrag Formation of Saskatchewan, Canada, and is re-interpreted as belonging to an indeterminate amphiumid genus and species. Contrary to a recent claim, P. cretacea is a diagnosable amphiumid taxon and stands as the geologically oldest member of the family. Proamphiuma differs from the type and only other unequivocal amphiumid genus, Amphiuma (four species: late Paleocene–Recent, USA), in primitively retaining weaker vertebral crests and processes. Proamphiuma differs further from the three extant Amphiuma species (conditions unknown for the late Paleocene A. jepseni) in three character states that are potentially autapomorphic within the family—indistinct postzygapophyseal process on atlas, vertebrarterial canal closed posteriorly in trunk vertebrae, and spinal foramen present in anterior caudals—plus vertebral plesiomorphies and one vertebral character state of uncertain polarity. The following relationships are hypothesized within the Amphiumidae: Proamphiuma (A. jepseni (A. pholeter (A. means + A. tridactylum))). This phylogeny and fossil occurrences imply that the characteristic atlanto–cranial joint and elongate trunk and the unique vertebromuscular complex of amphiumids were established by the Cretaceous–Tertiary boundary, while elongation of the snout and associated cranial modifications seen in living amphiumids appeared after the late Paleocene. In terms of its morphology and provenance, Proamphiuma remains a good structural ancestor for, if not directly ancestral to, Amphiuma.

Comparative morphology of the ilium of anurans and urodeles (Lissamphibia) and a re-assessment of the anuran affinities of Nezpercius dodsoni Blob et al., 2001

ABSTRACT Ilia of anurans (frogs) and urodeles (salamanders) are commonly recovered from microvertebrate fossil localities. Ilia in these clades are distinctive when complete and articulated with the rest of the pelvic girdle, but when preserved as isolated and broken fossils they may appear superficially similar. Reliable identification of urodele ilia is further hampered by limited information about the basic structure and contacts of the bone and its variation within the clade. Here we demonstrate that the ilium is more variable among urodeles than previously realized and provide the first detailed inventory of features that are potentially useful for differentiating ilia of anurans and urodeles. Many of these features relate to differences between the two clades in the orientation of the ilium and its contacts with other bones and with soft tissues. Based on the results of our survey, we re-interpret the holotype and two referred ilia of Nezpercius dodsoni (Late Cretaceous; Montana, U.S.A.) as being from an indeterminate urodele, not an anuran as originally described. Additional examples of Late Cretaceous urodele ilia are documented to highlight some of the variation seen in fossil urodele ilia and to aid in the proper identification of such specimens.

Redescription of the geologically youngest albanerpetontid (?Lissamphibia): Albanerpeton inexpectatum Estes and Hoffstetter, 1976, from the Miocene of France

Abstract Albanerpeton inexpectatum Estes and Hoffstetter, 1976 , the type species of Albanerpeton and the geologically youngest albanerpetontid, is rediagnosed and redescribed based on a large collection of jaws and frontals from Miocene fissure fills near La Grive-Saint-Alban, southeastern France. Intraspecific variation is documented in these elements, and is attributed to growth and individual differences. Synapomorphies of the upper jaws indicate that A. inexpectatum a) belongs in a clade whose members are otherwise known from the Upper Cretaceous-Paleocene of North America and b) is the sister species of an undescribed North American Paleocene species. The presence of A. inexpectatum in the Miocene of France is postulated to be the result of an Early or Middle Tertiary dispersal of an unknown ancestral species from North America into Europe. Cranial apomorphies of A. inexpectatum are interpreted as having strengthened the skull for burrowing in rocky soil and feeding.

The Euro-American genus Eopelobates, and a re-definition of the family Pelobatidae (Amphibia, Anura)

The extinct Eopelobates (Eocene of western North America; Eocene–Pliocene of Europe) and Pelobates (Oligocene–Recent of Europe; Recent of northern Africa and the Middle East) are superficially toad-like anurans that are united within the family Pelobatidae mainly on the basis of a unique, tripartite frontoparietal complex. Both genera have a relatively good fossil record consisting of isolated bones, skeletons, and developmental series of tadpoles through adults, all of which are potentially informative for tracing the evolutionary history of the family. Eopelobates is of interest for several reasons. Of the two pelobatid genera, Eopelobates appears earlier in the fossil record (early Eocene vs. late Oligocene) and it is more primitive in lacking many of the features associated with fossoriality in extant Pelobates. The taxonomic composition of Eopelobates has been contentious and at least one putative new species has long been recognised, but never formally named. Here, we provide updated taxonomic accounts for Pelobatoidea, Pelobatidae, Pelobates, and Eopelobates and document development within a series of tadpoles and juveniles of E. bayeri from Bechlejovice (late Oligocene in age), Czech Republic. We also provide updated accounts for the five previously named and currently accepted species of Eopelobates. For the European congeners, E. anthracinus (late Oligocene) and E. bayeri (early Oligocene–middle Miocene) can confidently be regarded as separate species; although the distinction between E. hinschei and E. wagneri (both middle Eocene) is less certain, we provisionally maintain them as separate species. Micro-CT scans for the holotype skeleton of E. grandis (latest Eocene, USA) help resolve some problematic features, most notably showing that the cranial sculpture is of the pit-and-ridge style that is typical for Eopelobates. A sixth congener is named and described based on two skeletons from the middle Eocene portion of the Green River Formation, in Wyoming, USA. We caution that reports of Eopelobates-like anurans from the pre-Eocene of western North America and the early Eocene of India are based on isolated bones that cannot be assigned with confidence to that genus. The presence of Eopelobates in both North America and Europe may be explained by dispersal via the high latitude land bridge that connected those two continents during the late Paleocene through Eocene. The pelobatid fossil record is informative for documenting the nature and timing of changes in cranial features (e.g. ornament patterns, shape of nasals, pattern of frontoparietal–squamosal contact) from the inferred primitive condition seen in most Eopelobates to the more derived condition seen in extant Pelobates, but it is less informative for tracing the evolution of fossoriality, which is a key attribute of extant Pelobates.

A New Albanerpetontid Amphibian from the Barremian (Early Cretaceous) Wessex Formation of the Isle of Wight, Southern England

A new albanerpetontid, Wesserpeton evansae gen. et sp. nov., from the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern England, is described. Wesserpeton is established on the basis of a unique combination of primitive and derived characters relating to the frontals and jaws which render it distinct from currently recognized albanerpetontid genera: Albanerpeton (Late Cretaceous to Pliocene of Europe, Early Cretaceous to Paleocene of North America and Late Cretaceous of Asia); Celtedens (Late Jurassic to Early Cretaceous of Europe); and Anoualerpeton (Middle Jurassic of Europe and Early Cretaceous of North Africa). Although Wesserpeton exhibits considerable intraspecific variation in characters pertaining to the jaws and, to a lesser extent, frontals, the new taxon differs from Celtedens in the shape of the internasal process and gross morphology of the frontals in dorsal or ventral view. It differs from Anoualerpeton in the lack of pronounced heterodonty of dentary and maxillary teeth; and in the more medial location and direction of opening of the suprapalatal pit. The new taxon cannot be referred to Albanerpeton on the basis of the morphology of the frontals. Wesserpeton currently represents the youngest record of Albanerpetontidae in Britain.

New albanerpetontid amphibians from the albian to Coniacian of Utah, Usa—Bridging the gap

ABSTRACT Newly discovered fossils described herein from Utah, USA, help fill a sizeable gap in the Cretaceous record of the Albanerpetontidae and provide information on the evolution of the family during the latest Early–middle Late Cretaceous. The geologically oldest record of sympatry among albanerpetontids is in the Mussentuchit Member (latest Albian–earliest Cenomanian in age), Cedar Mountain Formation, where two indeterminate species are recognized based on jaws. The first species primitively resembles geologically older albanerpetontids in the structure of the premaxilla and documents the last appearance of this more primitive premaxillary pattern. The second species closely resembles the North American Campanian–Maastrichtian species Albanerpeton nexuosus in derived premaxillary features, and is the earliest record both of a subgeneric clade that includes all congeners, except A. arthridion, and of a less inclusive clade of Euramerican Upper Cretaceous–Miocene species having premaxillary synapomorp...

Mesozoic and Palaeocene lissamphibian assemblages of North America: a comprehensive review

The Mesozoic and Palaeocene record of lissamphibians (i.e. anurans, caudates, gymnophionans and albanerpetontids) in North America is reviewed on the basis of over 400 published and unpublished occurrences from 61 geological formations. The record is heavily biased towards isolated bones, although some associated and articulated skeletons and rare tracks and trackways are known. Most of the localities are in the Western Interior: in central and southern Alberta and southern Saskatchewan, Canada, extending southwards through the USA and into northern Mexico. Outside of that region, records are limited to one Late Cretaceous age formation in Baja California and several Late Triassic and Cretaceous age formations in the eastern USA. Putative lissamphibians have been reported from the Late Triassic (middle Carnian and early Norian). Unambiguous lissamphibians are known from the Early Jurassic (Sinemurian–Pliensbachian), the Late Jurassic (Kimmeridgian–earliest Tithonian), the basal Cretaceous (late Berriasian–Valanginian) and a nearly continuous sequence extending from the Aptian through to the terminal Palaeocene. The Early Jurassic (Sinemurian–Pliensbachian) of Arizona documents the oldest global occurrences of an anuran (i.e. crown frog) and a stem caecilian; the latter also is the only North American fossil occurrence for Gymnophiona prior to the Quaternary. Late Jurassic (Kimmeridgian–earliest Tithonian) age deposits in Colorado, Utah and Wyoming contain a moderate diversity of anurans, urodeles (i.e. crown salamanders) and possibly stem salamanders. A basal Cretaceous locality (late Berriasian–Valanginian) in South Dakota contains a urodele and the first North American occurrence for Albanerpetontidae. Aptian/Albian age localities in Montana, Wyoming, Texas and Oklahoma contain a mixture of anurans, urodeles and albanerpetontids—that tripartite lissamphibian composition persists in North America through the remainder of the Cretaceous and intermittently through the Palaeocene. Most of the anurans are of uncertain familial affinities. The urodeles contain a mixture of extinct families (Scapherpetontidae and Batrachosauroididae) that were prominent through the Cretaceous into the early Palaeogene, along with the earliest appearances of several extant families, specifically sirenids in the Santonian, amphiumids and proteids in the late Maastrichtian and dicamptodontids and unequivocal cryptobranchids in the late Palaeocene. The albanerpetontid genus Albanerpeton was moderately diverse during the Cretaceous and Palaeocene, before vanishing from the North American record near the end of the Palaeocene. Temporal richness estimates of North American lissamphibians were calculated based on taxic and minimum lineage level occurrence data per 5 million year time interval beginning in the Early Jurassic and though to the end of the Palaeocene. The resulting richness curves demonstrate a general pattern of increasing richness leading up to the Cretaceous-Palaeogene (K-Pg) boundary, with peak values during the Campanian and Maastrichtian and a decline thereafter. The latter part of that pattern suggests higher extinction rates for lissamphibians across the K-Pg boundary compared to previous estimates, which we attribute to our coarser temporal binning, taxonomic additions and changes to some earlier taxonomic identifications. Although the overall richness pattern may at least partially reflect a true signal, it is heavily influenced by factors such as taphonomy, temporal gaps, fossil sampling and publication biases towards particular intervals and taxonomic groups; more detailed studies of all major lissamphibian clades are needed to corroborate these findings. This review highlights the strengths and weaknesses of the Mesozoic and Palaeocene portion of the North American lissamphibian record and provides a framework for future work.

MONOPHYLY AND INTRA-GENERIC RELATIONSHIPS OF ALBANERPETON (LISSAMPHIBIA; ALBANERPETONTIDAE)

Abstract The first phylogenetic analysis of the Euramerican Early Cretaceous–Miocene genus Albanerpeton is presented based on 16 characters of the jaws, frontals, and inferred body size scored for the seven recognized species in the genus and three other albanerpetontid taxa. Monophyly of Albanerpeton is corroborated and nested sets of synapomorphies yield the following hypothesized relationships: A. arthridion ((A. cifellii + A. galaktion + A. gracilis) (A. nexuosus (unnamed late Paleocene species + A. inexpectatum))). Osteological modifications identified in Albanerpeton initially involve the frontals, then shift largely to the jaws. Many of these changes are interpreted to be associated with broadening the head and strengthening the snout and jaws, presumably for feeding and burrowing. The first half or more (latest Aptian/earliest Albian to late Paleocene) of the known record for Albanerpeton and six of the seven species are restricted to the North American Western Interior. These occurrences and the phylogenetic framework proposed here suggest that the evolutionary history of Albanerpeton was centered in the Western Interior of North America.

Micro-Computed Tomography Study of a Three-Dimensionally Preserved Neurocranium of Albanerpeton (Lissamphibia, Albanerpetontidae) from the Pliocene of Hungary

ABSTRACT The Albanerpetontidae, small salamander-like tetrapods from the Middle Jurassic-Neogene of Laurasia and northern Africa, are widely considered to be lissamphibians; however, relationships among major lissamphibian clades are unresolved. A recently identified, isolated, and three-dimensionally preserved neurocranium (early Pliocene, Hungary) referred to Albanerpeton pannonicum is described, incorporating information gained from the application of micro-computed tomography. It is revealed that the neurocranium is a robust, box-like structure composed of the coossification of the parasphenoid, otic capsules, and occipital elements. The otic capsule endocast reveals the morphology of the endosseous labyrinth, complete with well-defined endosseous semicircular canals and a modestly developed ventral endosseous auditory region; however, details of the individual auditory organs are not discernable from the endocast. Features of the neurocranium and endosseous labyrinth are consistent with the hypothesis that A. pannonicum, and albanerpetontids in general, were somewhat fossorial. The neurocranium and endosseous labyrinth exhibit a mosaic of anuran, urodele, and apodan traits, thus precluding refinement of the phylogenetic position of albanerpetontids. In general, the neurocranium and endosseous labyrinth appear most similar to urodeles, and similarities with apodans and anurans may be due to convergent evolution resulting from similar habits and responses to inner ear stimulation. This new neurocranium represents the best-known specimen of its kind for albanerpetontids, and the data presented here combined with future comparative studies will contribute to a better understanding of the biology and evolution of this group.