Jack L. Conrad

Phylogeny and systematics of Squamata (Reptilia) based on morphology

Abstract Squamata (amphisbaenians, “lizards”, mosasaurs, and snakes) is an extremely diverse clade with a rich fossil record. There is little consensus about the interrelationships of the major squamate clades (i.e., Iguania, Gekkota, Scincomorpha, Anguimorpha, Amphisbaenia, and Serpentes), or even the membership of some of these clades. Morphology-based cladistic analyses typically agree only that the major dichotomy in extant squamates is between Iguania and all other taxa. The phylogenetic placement of Amphisbaenia and Serpentes is particularly problematic. Incomplete taxon sampling is likely a major contributing factor to the absence of a consensus about squamate interrelationships. This study examines squamate relationships using 222 ingroup taxa scored for 363 morphological characters. Analysis of these data recovered 2,213 equally short trees with a length of 3,273 steps and a retention index of 0.7164. The results confirm the monophyly of the clades Scleroglossa (extant squamates exclusive of Iguania), Gekkota, Scincomorpha, Lacertoidea, Scincoidea, Anguimorpha, Carusioidea, Platynota, and Varanoidea. Novel results include the identification of a clade containing Scincidae sensu lato, Dibamidae, Amphisbaenia, and Serpentes; identification of a Mesozoic clade containing Bainguis, Eoxanta lacertifrons, Globaura venusta, and Myrmecodaptria; and identification of Dalinghosaurus as a basal shinisaur. A new taxonomic scheme is outlined. The names Iguanomorpha, Scincogekkonomorpha, Evansauria, and Mosasauriformes are applied to the stem-based groups including Iguania, Scleroglossa, Autarchoglossa, and Mosasauria, respectively. The importance of strict rigidity within taxonomy is questioned; taxonomy is most useful as a tool for communication about organisms or groups of organisms.

A combined evidence phylogenetic analysis of Anguimorpha (Reptilia: Squamata)

Anguimorpha is a clade of limbed and limbless squamates with ca. 196 extant species and a known fossil record spanning the past 130 million years. Morphology‐based and molecule‐based phylogenetic analyses disagree on several key points. The analyses differ consistently in the placements of monstersaurs (e.g. Gila Monsters), shinisaurs (Crocodile Lizards), the anguid Anniella (American Legless Lizards), carusioids (Knobby Lizards), and the major clades within Varanus (Monitor Lizards). Given different data sources with such different phylogenetic hypotheses, Anguimorpha is an excellent candidate for a combined phylogenetic analysis. We constructed a data matrix consisting of 175 fossil and extant anguimorphs, and 2281 parsimony‐informative characters (315 morphological characters and 1969 molecular characters). We analysed these data using the computer program TNT using the “new technology search” with the ratchet. Our result is novel and shows similarities with both morphological and molecular trees, but is identical to neither. We find that a global combined evidence analysis (GCA) does not recover a holophyletic Varanoidea, but omission of fossil taxa reveals cryptic molecular support for that group. We describe these results and others from global morphological analysis, extant‐only morphological analysis, molecular data‐only analyses, combined evidence analysis of extant taxa, and GCA.

The Theropod Furcula

The furcula is a structure formed by the midline fusion of the clavicles. This is the element which is unique to theropods and is important for understanding the link between birds and other theropods. New specimens from basal theropods suggest that the furcula appeared very early in theropod history. We review furcula development, function, and morphology, as well as the anatomical terminology applied to it. Furcular morphology is highly variable in crown‐group avians but is rather conserved among nonavian theropods. Here we review, or describe for the first time, the furculae in many nonavian theropods. Furculae occur in nearly all major clades of theropods, as shown by new theropod specimens from the Early Cretaceous of China and a close inspection of previously collected specimens. Informative phylogenetic characters pertaining to the furcula occur throughout Theropoda, though care should betake to consider taphonomic effects when describing furcular morphology. J. Morphol., 2009.

High-resolution X-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öösh (Övörkhangai; Mongolia)

We describe the braincase of AMNH FR 21444, a gecko-like squamate from the Early Cretaceous of Mongolia, based on high-resolution X-ray computed tomography scans (CT scans) and incorporate it in a phylogenetic analysis of 36 squamate taxa scored for 226 morphological characters. Our analysis corroborates the Eublepharidae-Gekkonoidea split as the basal gekkotan dichotomy, but retrieves Teratoscincus as the sister-taxon to pygopodines + diplodactylines. The combination of plesiomorphic and apomorphic character states within AMNH FR 21444 demonstrates a decoupled evolutionary history between the braincase and the rest of the skull and mandible within gekkonomorph squamates. Enclosure of the lateral head vein and mandibular branch of the trigeminal nerve are both plesiomorphic for gekkonomorphs. The mechanisms responsible for the transition from the plesiomorphic skull roof of basal gekkonomorphs to the modern gekkotan condition cannot be anticipated given the current data.

A Complete Late Cretaceous Iguanian (Squamata, Reptilia) from the Gobi and Identification of a New Iguanian Clade

Abstract Iguania is a diverse clade with an incompletely known fossil record. Here, we describe and name the earliest iguanian known from a complete skeleton. The specimen (IGM 3/858) comes from Ukhaa Tolgod (Upper Cretaceous of Mongolia) and offers important insights into the evolutionary history of iguanian osteology. The new taxon is diagnosed by a combination of character states, including the presence of a frontoparietal fontanelle, absence of an enlarged nuchal fossa, and unflared tooth crowns. We performed a cladistic analysis including 54 taxa scored for 202 informative morphological characters. A strict consensus of 46 shortest recovered trees reveals that the new taxon is a basal member of a previously unidentified clade of Cretaceous iguanians, probably endemic to the Gobi. This clade of Gobi iguanians is nested within a monophyletic Pleurodonta (non-acrodontan iguanians).

A GREEN RIVER (EOCENE) POLYCHROTID (SQUAMATA: REPTILIA) AND A RE-EXAMINATION OF IGUANIAN SYSTEMATICS

Abstract A pleurodontan iguanian from the Green River Formation (Eocene) is described in detail and named. The new taxon is known only from a single specimen preserving all areas of the body. Although many of the bone surfaces are eroded, almost all of the skeleton is present and some cartilaginous elements are preserved. The new taxon shares important characteristics with the extant anisolepines and leiosaurines, including the morphology and placement of the caudal autotomy planes, the postxiphisternal inscriptional ribs, and notched or fenestrated clavicles that are expanded proximally. This is the earliest complete iguanian known from the Americas and the earliest known iguanian that may be confidently referred to an extant “family.” A phylogenetic analysis including this taxon and other fossil and extant iguanians offers some support for the monophyly of Polychrotidae sensu lato, Tropiduridae sensu lato, and non-acrodont iguanians (Pleurodonta).

A New Platynotan Lizard (Diapsida: Squamata) from the Late Cretaceous Gobi Desert (Ömnögov), Mongolia

Abstract Here we describe a new diminutive varanoid from the Late Cretaceous Djadoktha Formation of Omnogov, Mongolia. The new taxon, Ovoo gurval, was found in the Nemegt Basin at the locality of Little Ukhaa, a locality adjacent to the rich fossil beds of Ukhaa Tolgod. The new varanoid is similar to Aiolosaurus oriens, another small varanoid from the Ukhaa Tolgod locality and several diagnostic characters of Ovoo gurval are shared with Aiolosaurus oriens. Ovoo gurval also has a pair of unusual neomorphic ossifications on the skull roof overlying the frontonasal contact. Positionally, these are unlike any neomorphic ossifications in other squamates, and certainly can be distinguished from osteoderms found in some varanoids.

Earliest example of a giant monitor lizard (Varanus, Varanidae, Squamata).

Background Varanidae is a clade of tiny (<20 mm pre-caudal length [PCL]) to giant (>600 mm PCL) lizards first appearing in the Cretaceous. True monitor lizards (Varanus) are known from diagnostic remains beginning in the early Miocene (Varanus rusingensis), although extremely fragmentary remains have been suggested as indicating earlier Varanus. The paleobiogeographic history of Varanus and timing for origin of its gigantism remain uncertain. Methodology/Principal Findings A new Varanus from the Mytilini Formation (Turolian, Miocene) of Samos, Greece is described. The holotype consists of a partial skull roof, right side of a braincase, partial posterior mandible, fragment of clavicle, and parts of six vertebrae. A cladistic analysis including 83 taxa coded for 5733 molecular and 489 morphological characters (71 previously unincluded) demonstrates that the new fossil is a nested member of an otherwise exclusively East Asian Varanus clade. The new species is the earliest-known giant (>600 mm PCL) terrestrial lizard. Importantly, this species co-existed with a diverse continental mammalian fauna. Conclusions/Significance The new monitor is larger (longer) than 99% of known fossil and living lizards. Varanus includes, by far, the largest limbed squamates today. The only extant non-snake squamates that approach monitors in maximum size are the glass-snake Pseudopus and the worm-lizard Amphisbaena. Mosasauroids were larger, but exclusively marine, and occurred only during the Late Cretaceous. Large, extant, non-Varanus, lizards are limbless and/or largely isolated from mammalian competitors. By contrast, our new Varanus achieved gigantism in a continental environment populated by diverse eutherian mammal competitors.

Osteology of Gobiderma pulchrum (Monstersauria, Lepidosauria, Reptilia)

Abstract Joint expeditions by the American Museum of Natural History and Mongolian Academy of Sciences have recovered significant new remains of the basal monstersaur Gobiderma pulchrum. We describe these new specimens in detail and also revisit the originally described material in order to more fully understand this pivotal anguimorph taxon. The newly discovered specimens include skull and postcranial materials that add dramatically to the understanding of the osteology of Gobiderma pulchrum. We revise the diagnosis of this species, adding to the previously published diagnosis the following character states: premaxillary nasal process is narrowest mediolaterally; postfrontal and postorbital remain unfused; postorbital extends posteriorly for almost the entire length of the supratemporal fenestra; the Vidian canal is posteriorly enclosed by the parabasisphenoid; an anterior coracoid emargination is present; the pelvis is completely fused; and the lateral plantar tubercle is distally placed. A phylogenetic analysis confirms the placement of Gobiderma pulchrum as a non-helodermatid monstersaur. As such, the fact that it is known from reasonably complete remains makes it pivotal for understanding character evolution within Monstersauria. The Djadokhta Formation includes several carnivorous/insectivorous lizards and theropod dinosaurs—more than is usual for extant communities, but perhaps analogous in some ways to parts of modern Australia.

The braincases of two glyptosaurines (Anguidae, Squamata) and anguid phylogeny

Abstract Glyptosaurines are an extinct clade of anguids whose remains are common in many Holarctic Paleogene and Cretaceous deposits. Despite their extensive fossil record (comprised mainly of scutes) the braincase is poorly known. Here, we describe braincase morphology in two North American Eocene glyptosaurines, Melanosaurus maximus and Helodermoides tuberculatus. Although generally conservative in their braincase morphology compared with other anguids, these taxa and some other “higher” glyptosaurines possess a dorsally displaced parasphenoid rostrum. The anterior openings for the Vidian canals open almost directly ventral to the parasphenoid rostrum, and the internal carotids exit anteriorly almost directly dorsal to it. Our phylogenetic analysis recovers a monophyletic Glyptosaurinae nested within Anguidae as the sister taxon to a clade containing Gerrhonotinae and Anguinae. According to our analysis, “melanosaurins” are paraphyletic, Placosaurus is paraphyletic, and Anniella is the sister taxon to Anguis.