Randall L. Nydam

NEW TAXA OF TRANSVERSELY-TOOTHED LIZARDS (SQUAMATA: SCINCOMORPHA) AND NEW INFORMATION ON THE EVOLUTIONARY HISTORY OF “TEIIDS”

Abstract New material of polyglyphanodontine lizards from the Late Cretaceous has been found in various localities in western North America. Several transversely oriented teeth representing a new species of Dicothodon were recovered from the Turonian of southern Utah. These specimens necessitate reassignment of Polyglyphanodon bajaensis to Dicothodon (Polyglyphanodon) bajaensis. From the Campanian of Utah, additional teeth and jaw fragments referable to Manangysaurus saueri have been recovered and this species is reassigned here to Peneteius (Manangysaurus) saueri. Also, an isolated tooth referable to Peneteius has been recovered from the Campanian of southern Texas. The results of a phylogenetic analysis support a monophyletic grouping of the transversely-toothed taxa with Bicuspidon as the sister taxon of Polyglyphanodontini new taxon, which is comprised of Polyglyphanodon, Dicothodon, and Peneteius. The phylogenetic analysis also places “teiid” lizards from the Cretaceous of Asia and North America in a monophyletic group, Borioteiioidea new taxon, which is the sister taxon to the Teiioidea (Teiidae + Gymnophthalmidae). This new hypothesis of the interrelationships of these taxa requires the reevaluation of several characteristics that were previously considered diagnostic for a more inclusive Teiidae. Another implication of our results is that Teiidae (sensu stricto) has no demonstrable pre-Tertiary occurrence. It appears that Teiioidea and Borioteiioidea diverged from a common ancestor by the Early Cretaceous. The Teiioidea entered South America and are currently represented by the Teiidae and Gymnophthalmidae, whereas Borioteiioidea radiated throughout North America with subsequent dispersal to Asia and Europe.

A new teiid lizard from the Cedar Mountain Formation (Albian–Cenomanian Boundary) of Utah

Abstract A heretofore unknown teiid lizard, recovered from the Cedar Mountain Formation (Albian–Cenomanian boundary) of Emery County, Utah, is the oldest teiid that is represented by numerous specimens. This new taxon has a heterodont dentition with conical anterior teeth and transversely oriented bicuspid posterior teeth that are distinct from those of Peneteius (Late Cretaceous) and Teius and Dicrodon (Recent). It also shows ontogenetic variation in tooth shape, in which the posterior teeth become more massive and have more transversely expanded crowns, as the individual grows older. Further comparisons and analysis indicate (1) that North American Cretaceous Polyglyphanodontinae (characterized by teeth with transversely-oriented crests) achieved their unusual dental specializations independently from those of analogous modern taxa; (2) that their transverse tooth-cresting resulted from addition of a medial cusp (rather than crown rotation, as previously hypothesized and which apparently is the case for living taxa); and (3) that the species from the Cedar Mountain Formation represents a sister-taxon to other North American polyglyphanodontines Polyglyphanodon, Peneteius and presumably Paraglyphanodon and Dicothodon. The new taxon thus represents an example of the morphologically antecedent dental specializations that culminated in the strikingly specialized dentition of Polyglyphanodon sternbergi.

The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution

The previous oldest known fossil snakes date from ~100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ~70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.

Giant taxon-character matrices: quality of character constructions remains critical regardless of size

Giant morphological data matrices are increasingly common in cladistic analyses of vertebrate phylogeny, reporting numbers of characters never seen or expected before. However, the concern for size is usually not followed by an equivalent, if any, concern for character construction/selection criteria. Therefore, the question of whether quantity parallels quality for such influential works remains open. Here, we provide the largest compilation known to us of character construction methods and criteria, as derived from previous studies, and from our own de novo conceptualizations. Problematic character constructions inhibit the capacity of phylogenetic analyses to recover meaningful homology hypotheses and thus accurate clade structures. Upon a revision of two of the currently largest morphological datasets used to test squamate phylogeny, more than one‐third of the almost 1000 characters analysed were classified within at least one of our categories of “types” of characters that should be avoided in cladistic investigations. These characters were removed or recoded, and the data matrices re‐analysed, resulting in substantial changes in the sister group relationships for squamates, as compared to the original studies. Our results urge caution against certain types of character choices and constructions, also providing a methodological basis upon which problematic characters might be avoided.

Borioteiioidean lizard skulls from Kleskun Hill (Wapiti Formation; upper Campanian), west-central Alberta, Canada

ABSTRACT New material of borioteiioidean lizards (Squamata: Scincomorpha) from west-central Alberta, Canada, represent the first and northernmost record of multiple articulated skull elements from the Cretaceous of North America. Specimens were recovered from the fluvial beds of the Wapiti Formation (Campanian) within a bentonitic paleosol exposed at the Kleskun Hill Park, east of the city of Grande Prairie. Such beds accumulated during the maximum transgression of the Bearpaw Seaway (73–74 Ma), thus providing crucial information on lizard faunas during a time interval represented in most of coeval North American deposits by marine strata. Cranial material ascribed to Socognathus unicuspis give the occasion for a revision of the taxon with respect to osteologically better-known Polyglyphanodon sternbergi from the Late Cretaceous of Utah as well as a comparison with several lizards reported from coeval strata of Mongolia. Furthermore, a new scincomorphan lizard, Kleskunsaurus grandeprairiensis, gen. et sp. nov., is described. Socognathus unicuspis is assigned to Chamopsiidae, taxon nov., which also includes Chamops, Leptochamops, and several other morphologically similar taxa from the Cretaceous of North America.

Squamates from the Jurassic and Cretaceous of North America

Squamates from the Mesozoic of North America have been collected since the end of the nineteenth century. To date, the fossils are known to occur in the Late Jurassic, Aptian-Albian, Cenomanian, Turonian, Santonian, Campanian, and Maastrichtian. Most of the records are from the Western Interior in the arid regions associated with the Rocky Mountains. Geographically, these records extend from central Alberta, Canada, south to northern Mexico. The earliest squamates are primitive forms of scincoideans and anguimorphans from the Late Jurassic–Early Cretaceous. At the beginning of the Late Cretaceous, the squamate fauna in North America changes dramatically to include a much greater diversity of taxa with a mix of lineages now extinct (e.g. Polyglyphanodontini, Chamopsiidae, Contogeniidae) and lineages still alive today (e.g. Anguidae, Xantusiidae, Platynota, Serpentes). The greatest diversity appears to be during the late Campanian, but diversity appears correlated with number of localities sampled and the late Campanian is the best sampled horizon in the Mesozoic of North America. The apparent sudden change in the North American squamate fauna is coincident with similar changes to other vertebrates (mammals, dinosaurs) and the opening of a land bridge with Asia. The lack of taxonomic and systematic study of the squamates from the Early Cretaceous of Asia makes comparison difficult, but it is likely that introduction of Asian taxa into North America was responsible, at least in part, for the relatively rapid change in the North American fauna. The hypotheses of an additional invasion from Asia during the Turonian is not supported, but the hypothesis of a second opening with Asia during the Santonian is weakly supported by the appearance of an iguanian in North America. Additional iguanians from the Campanian may have evolved in situ or may have entered North America from Asia as late as the mid-Campanian. Many of the most conspicuous lizards of the Late Cretaceous (Polyglyphanodontini, Chamopsiidae, paramacellodid-cordylid grade scincoideans) went extinct at the terminal Cretaceous extinction event, while most of the anguimorphans and snakes appear little affected. Amphisbaenians do not appear in North America until after the early Paleocene.

The occurrence of Contogenys-like lizards in the Late Cretaceous and Early Tertiary of the western interior of the U.S.A.

ABSTRACT Based on diagnostic jaw and dental material from the Cenomanian—middle Paleocene of the western U.S.A., we erect a new fossil lizard taxon, Contogeniidae taxon nov., that contains the following species: Contogenys sloani Estes, 1969 (Maastrichtian—early Paleocene, Montana); Contogenys ekalakaensis sp. nov. (middle Paleocene, Montana); Palaeoscincosaurus middletoni Sullivan and Lucas, 1996 (early Paleocene, Colorado); Palaeoscincosaurus pharkidodon sp. nov. (Campanian, Utah); Utahgenys evansi gen. et sp. nov. (Turonian, Utah); and Utahgenys sp. indet. (Cenomanian, Utah). These taxa share unique characteristics of tooth and jaw morphologies (e.g., tooth crowns truncate and bearing longitudinal apical grooves; hypertrophied inferior alveolar canal). Phylogenetic analysis indicates that among squamates, Contogeniidae taxon nov. is most closely related to Xantusiidae.

Reevaluation of the anatomy of the Cenomanian (Upper Cretaceous) hind-limbed marine fossil snakes Pachyrhachis, Haasiophis, and Eupodophis

ABSTRACT New anatomical observations and reinterpretations of previously identified structures have resulted in new taxonomic diagnoses for the fossil hind-limbed marine snakes Pachyrhachis problematicus, Eupodophis descouensi, and Haasiophis terrasanctus. Among the most important conclusions of our study are the following: Haasiophis and Eupodophis show no evidence of possessing a laterosphenoid; Pachyrhachis and Eupodophis do retain a jugal; Haasiophis, like Eupodophis, has chevron bones in the caudal region; Haasiophis has a large number of unfused intercentra along the anterior portion of the precloacal column; the dentary of Pachyrhachis has numerous mental foramina (at least four); Pachyrhachis has at least one sacral vertebra with unfused sacral ribs. To test the effect of our new observations on the phylogenetic relationships of snakes, we ran three phylogenetic analyses using alternative outgroups to polarize the character transformations. The ingroup consisted of all well-preserved fossil snakes from the Cretaceous, the madtsoiids, and taxa that are representative of all major groups of extant snakes. The analyses yielded a series of most parsimonious trees that placed Pachyrhachis, Eupodophis, and Haasiophis either as a series of stem taxa at the base of the radiation of snakes (two analysis), or as members of a clade of fossil snakes that are the sister group of all living alethinopidians (one analysis).

Lizards and snakes of the Terlingua Local Fauna (late Campanian), Aguja Formation, Texas, with comments on the distribution of paracontemporaneous squamates throughout the Western Interior of North America

ABSTRACT The late Campanian—aged (= Judithian) squamates from the Terlingua Local Fauna of the Aguja Formation, southern Texas, includes four scincomorphans: a new taxon (Catactegenys solaster, gen. et sp. nov.), referable to Xantusiidae, that has massive teeth and tooth crown morphology similar to that of contogeniid lizards; an indeterminate scincomorphan (Apsgnathus triptodon, gen et sp. nov.) with robust teeth; and two unnamed scincomorphan morphotypes. Anguimorphans in the fauna include Odaxosaurus piger, cf. Parasaniwa wyomingensis, and a likely xenosaur. Ophidian jaw fragments confirm the presence of a snake in the fauna. The Aguja squamate assemblage is one of the most southerly of a series of paracontemporaneous squamate faunas extending from central Alberta to northern Mexico. Comparison of these faunas reveals that, although two taxa are endemic to the Aguja Formation, others show some latitudinal trends. Odaxosaurus and Parasaniwa are present in all well-sampled faunas from Alberta to Texas. The mammal-like Peneteius and snakes are found only in faunas from southern Utah to Mexico. Chamopsiids are only present from Alberta to New Mexico. The sole representatives of Contogeniidae and Xantusiidae are restricted to southern Utah and southern Texas, respectively. These hypotheses of distributional patterns must continue to be tested through ongoing investigations of all of the relevant faunas from the late Campanian of the Western Interior. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution

Temporal fenestration has long been considered a key character to understand relationships amongst reptiles. In particular, the absence of the lower temporal bar (LTB) is considered one of the defining features of squamates (lizards and snakes). In a re-assessment of the borioteiioid lizard Polyglyphanodon sternbergi (Cretaceous, North America), we detected a heretofore unrecognized ontogenetic series, sexual dimorphism (a rare instance for Mesozoic reptiles), and a complete LTB, a feature only recently recognized for another borioteiioid, Tianyusaurus zhengi (Cretaceous, China). A new phylogenetic analysis (with updates on a quarter of the scorings for P. sternbergi) indicates not only that the LTB was reacquired in squamates, but it happened independently at least twice. An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release. The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages. This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.