Sean P. Modesto

The phylogenetic definition of reptilia.

Naming taxa is an important endeavor in the documentation of life by systematists, whether it is conducted in the context of traditional rank-based classification or within a phylogenetic framework. Proponents of the phylogenetic approach distinguish between the diagnosis of a group and its definition (Ghiselin, 1984; Rowe, 1987, 1988), and this distinction forms the basis for a phylogenetically based method of naming taxa formerly referred to as Phylogenetic Taxonomy (de Queiroz and Gauthier, 1990, 1992, 1994) and now called Phylogenetic Nomenclature (PN; Cantino et al., 1999; Gauthier and de Queiroz, 2001; Bryant and Cantino, 2002). Emphasis in naming has been placed on ancestry using phylogenetic definitions, and the widespread adoption of nodeand stem-based definitions (apomorphy-based definitions have yet to receive as widespread acceptance, but see Gauthier and de Queiroz, 2001; Anderson, 2002; Laurin and Anderson, 2004) has led to a proliferation of new names and definitions. This shift in nomenclatural practice has, unfortunately, fostered a growth in redundant names and definitions for well-known taxa (Benton, 2000). The PhyloCode (Cantino and de Queiroz, 2003) has modified the rule of priority as used in other codes (i.e., International Code of Zoological Nomenclature) to determine which of two or more possible names with equivalent definitions is valid (Brochu and Sumrall, 2001), or which of several definitions for a given name is valid (Cantino and de Queiroz, 2003). Unfortunately, it is now apparent that some of the definitions for wellknown taxon names established early in the emergence of PN were not devised following conventions now widely accepted, by either defining groups in an overly restrictive manner, or via selection of reference taxa without due consideration of the ramifications of differing tree topologies (Anderson, 2002; Laurin and Anderson, 2004). It has become evident in broad-scale amniote taxonomy that the first published definition for Reptilia (Gauthier et al., 1988a), which would have priority under a binding PhyloCode, is problematic because of the dramatic controversies over the affinities of the specifier taxon Testudines (see Zardoya and Meyer, 2001 for review of hypotheses for turtle relationships). Recent morphological and molecular studies have challenged conventional hypotheses concerning the affinities of turtles, and this has led to unexpected and undocumented changes in the composition of the well-known taxon Reptilia, with additional ramifications for the nomenclature of some of its included taxa. We examine the consequences of the application of priority to the nomen Reptilia as our understanding of early amniote interrelationships has progressed over the past two decades, and offer a new definition that brings the phylogenetic concept of this taxon name into line with both currently accepted conventions of PN and historical usage. This new definition corrects an error created by the combination of the selection of a higher taxon (rather than a species) as a specifier, and an unexpected topology. We believe that now is an appropriate time to examine the definitions established when PN was in its earliest stages, and hope to correct what we consider to be a poorly formulated definition upon publication of a binding PhyloCode.

A New Triassic Owenettid Parareptile And The Mother Of Mass Extinctions

SEAN P. MODESTO1, ROSS J. DAMIANI2, JOHANN NEVELING3, and ADAM M. YATES4 1Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213 U.S.A., modestos@carnegiemuseums.org; 2Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Johannesburg, Private Bag 3, PO Wits, 2050, South Africa; 3Council for Geoscience, Private Bag X112, Pretoria, 0001, South Africa; 4Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom

A mixed-age classed ‘pelycosaur’ aggregation from South Africa: earliest evidence of parental care in amniotes?

Living species of mammals, crocodiles and most species of birds exhibit parental care, but evidence of this behaviour is extremely rare in the fossil record. Here, we present a new specimen of varanopid ‘pelycosaur’ from the Middle Permian of South Africa. The specimen is an aggregation, consisting of five articulated individuals preserved in undisturbed, close, lifelike, dorsal-up, subparallel positions, indicating burial in ‘life position’. Two size classes are represented. One is 50% larger than the others, is well ossified, has fused neurocentral sutures and is distinguished by a coat of dermal ossifications that covers the neck and shoulder regions. We regard this individual to be an adult. The remaining four skeletons are considered to be juveniles as they are approximately the same size, are poorly ossified, have open neurocentral sutures and lack dermal ossifications. Aggregates of juvenile amniotes are usually siblings. Extant analogues of adult and juvenile groupings suggest that the adult is one of the parents, leading us to regard the aggregation as a family group. The Late Middle Permian age of the varanopid family predates the previously known oldest fossil evidence of parental care in terrestrial vertebrates by 140 Myr.

A new basal dicynodont from the Upper Permian of South Africa

The skull of a small anomodont therapsid, from the Tapinocephalus Assemblage Zone (Abrahamskraal Formation, Beaufort Group, Upper Permian) in Northern Cape Province, South Africa, represents a new basal dicynodont and is described in detail. Colobodectes cluveri gen. et sp. nov. is distinguished from other dicynodonts by an anteroposteriorly extensive caniniform process, parietals that were broadly overlapped posterolaterally by posterodorsal processes of the postorbitals, diverging anterior palatal ridges, and a dorsoventrally low foramen magnum. A phylogenetic analysis indicates that Colobodectes is the basalmost member of a dicynodont clade that excludes Eodicynodon. This position is not particularly strong, as two additional steps are needed to make Colobodectes and Eodicynodon oosthuizeni exchange places on the most parsimonious tree. Another discovery of the phylogenetic analysis is that there is little basis for recognizing Eodicynodon oelofseni as the closest relative of E. oosthuizeni. The former species is identified as the sister taxon of a clade that includes the latter and all other dicynodonts.

HELEOSAURUS SCHOLTZI FROM THE PERMIAN OF SOUTH AFRICA: A VARANOPID SYNAPSID, NOT A DIAPSID REPTILE

ensis from Upper Carboniferous rocks of central North America (Reisz and Dilkes, 2003), whereas the youngest described members are the Middle Permian Mesenosaurus romeri and Pyozia mesenensis from Russia, and Elliotsmithia longiceps from South Africa (Anderson and Reisz 2003; Dilkes and Reisz, 1996; Reisz et al., 1998; Modesto et al., 2001). The monitor lizard-like aspect of some varanopids has generated some confusion with regards to their taxonomic affinities. Mesenosaurus romeri was first recognized as a varanopid (Efremov, 1940), but was later identified as an archosaurian diapsid reptile (Ivachnenko and Kurzanov, 1979); a detailed description and reappraisal has affirmed the original taxonomic assessment (Reisz and Berman, 2001). The holotype of A. hamiltonensis was heralded as a new, early diapsid (Reisz, 1988), one that was suspected to be a more crownward taxon (Laurin, 1991) than the Pennsylvanian diapsid Petrolacosaurus kansensis (Reisz, 1977). The formal description of A. hamiltonensis by Dilkes and Reisz (2003) demonstrated that it was a varanopid. All of the above mentioned varanopids were relatively small carnivores, equivalent to or slightly smaller in size than Mycterosaurus longiceps, known from Lower Permian rocks in Texas and Oklahoma (Reisz et al., 1997). However, Varanopidae also includes larger predators, members of the clade Varanodontinae: Aerosaurus, Varanops, Varanodon, and Watongia (Reisz and Laurin, 2004). All of these larger varanopids, ranging in size from 1.5 to greater than 2 m in total length, are restricted to North American strata.

The procolophonoid reptile Sauropareion anoplus from the lowermost Triassic of South Africa

Abstract The holotype of Sauropareion anoplus, a procolophonoid reptile from the Lystrosaurus Assemblage Zone of the Beaufort Group, lowermost Triassic of South Africa, is described in detail. New information includes the presence of fields of teeth on the vomer, the palatine, and the pterygoid, and the presence of a relatively long, tear-shaped interpterygoid vacuity. The parabasisphenoid features relatively broad posterolateral wings. A cleithrum is present. An entepicondylar foramen is present, but neither an ectepicondylar foramen nor a supinator process are present. We coded Sauropareion for the data matrices in two recent studies that had excluded this genus from consideration in phylogenetic analyses. Running of these slightly augmented matrices results in numerous optimal trees (8 and 15 optimal trees), i.e. the inclusion of Sauropareion greatly weakens the resolution of the tree topologies; in one case the inclusion of Sauropareion highlights the lack of anatomical information available for most procolophonids, and in the other it reveals weaknesses that are possibly attributable to character selection. We conducted a new phylogenetic analysis of Procolophonoidea, incorporating new phylogenetic characters from other studies. Our results confirm the position of S. anoplus as the sister taxon of a clade comprising all procolophonoids exclusive of Coletta seca. New phylogenetic definitions are devised for Owenettidae and Procolophonidae, making the latter one of the two primary clades within Procolophonoidea; Owenettidae and Procolophonidae are now sister taxa. As a result, the non-owenettid procolophonoids species S. anoplus and C. seca can be recognized as the most basal members of Procolophonidae.

Reassessment of the morphology and paleobiology of the therocephalian Tetracynodon darti (Therapsida), and the phylogenetic relationships of Baurioidea

ABSTRACT Several new specimens of the Triassic therocephalian Tetracynodon darti have become available in recent years, allowing substantial corrections and expansions to previous descriptions. We here analyze T. darti in the context of therocephalian relationships and biology, using computed tomographic (CT) scanning to reveal details of the skull. Histological sections, as well as the degree of ossification of individual elements, both suggest that the available specimens are subadults (rather than rapidly growing neonates), and probably yearlings. A maxillary shelf bearing a long suture with the vomer similar to that of Lycideops is present, and T. darti also shares a nasal-lacrimal contact with that taxon. There is no evidence for the presence of maxilloturbinal bones. The postcranial skeleton is slender and similar to that of regisaurids and other small baurioids. The skull bones show clear indentations demarcating the major divisions of the brain, allowing one of the most detailed reconstructions of a non-mammalian therapsid brain published to date. The brain is strikingly plesiomorphic in many features, particularly in the retention of large dorsally positioned optic lobes of the tectum, but generally shows features that are intermediate between gorgonopsians and cynodonts, thus clarifying this stage of the evolution of the synapsid brain. A cladistic analysis of 33 therapsid taxa and 131 morphological characters supports the monophyly of Therocephalia, and there is evidence for a monophyletic Lycideopidae within Baurioidea. Lycideopidae contains species with long snouts, nasal-lacrimal contacts, and incipient secondary palates, including Lycideops, Choerosaurus, T. tenuis, and T. darti.

A new Early Permian reptile and its significance in early diapsid evolution

The initial stages of evolution of Diapsida (the large clade that includes not only snakes, lizards, crocodiles and birds, but also dinosaurs and numerous other extinct taxa) is clouded by an exceedingly poor Palaeozoic fossil record. Previous studies had indicated a 38 Myr gap between the first appearance of the oldest diapsid clade (Araeoscelidia), ca 304 million years ago (Ma), and that of its sister group in the Middle Permian (ca 266 Ma). Two new reptile skulls from the Richards Spur locality, Lower Permian of Oklahoma, represent a new diapsid reptile: Orovenator mayorum n. gen. et sp. A phylogenetic analysis identifies O. mayorum as the oldest and most basal member of the araeoscelidian sister group. As Richards Spur has recently been dated to 289 Ma, the new diapsid neatly spans the above gap by appearing 15 Myr after the origin of Diapsida. The presence of O. mayorum at Richards Spur, which records a diverse upland fauna, suggests that initial stages in the evolution of non-araeoscelidian diapsids may have been tied to upland environments. This hypothesis is consonant with the overall scant record for non-araeoscelidian diapsids during the Permian Period, when the well-known terrestrial vertebrate communities are preserved almost exclusively in lowland deltaic, flood plain and lacustrine sedimentary rocks.

A burrow cast with Lystrosaurus skeletal remains from the Lower Triassic of South Africa

Abstract We report on a large burrow cast with skeletal contents from Lower Triassic strata of the Palingkloof Member of the Balfour Formation, which forms the lowermost portion of the Lystrosaurus Assemblage Zone (LAZ) of South Africa. The burrow cast is similar to large burrow casts previously described from the LAZ that were identified as large-scale Scoyenia domichnia. It is the first large burrow cast from the LAZ found to contain diagnostic fossil bone. The burrow cast is a relatively straight, subhorizontal (inclined ∼12°), dorsoventrally compressed tube consisting of an entry ramp and living chamber; the entrance to the burrow is not preserved and there is no evidence that the ramp formed a spiral section. The skeletal material comprises a single, partial, disarticulated skeleton of a juvenile animal that can be assigned with confidence to the dicynodont genus Lystrosaurus. Whereas similar large-diameter burrow casts from strata slightly higher in the LAZ have been attributed to Lystrosaurus, we present an alternative hypothesis that a carnivorous tetrapod constructed the burrow. Our preferred hypothesis is supported by the observation that the interred Lystrosaurus skeleton is too small to be the maker of this particular burrow, by the general observation that carnivorous tetrapods construct relatively straight burrows, and by the partial, disarticulated state of the skeleton, which we interpret as the remains of larded prey. We suggest that akidnognathid theriodonts of the genera Moschorhinus or Olivierosuchus, the most conspicuous large predators of the LAZ, were the constructors of large-diameter, subhorizontal burrows.

New Material of Colobomycter Pholeter, a Small Parareptile from the Lower Permian of Oklahoma

Abstract A new specimen of the parareptile Colobomycter pholeter, from the Lower Permian Dolese Brothers Quarry near Fort Sill, Oklahoma, preserves previously unknown portions of the skull, including the premaxilla, elements of the palate, and the sphenethmoid. The premaxilla houses two teeth, of which the first is caniniform in size. The pattern and the morphology of the upper dentition indicates that C. pholeter was a small faunivore. Fortuitous damage to the dentition reveals that the large marginal teeth are polyplocodont, the simplest kind of folded teeth. The folding may have strengthened the crowns of teeth, which were otherwise relatively thin-walled in C. pholeter. Considering its small size, C. pholeter was either an insectivore that specialized on prey with hard exoskeletons, or an insectivore that was facultatively carnivorous, capable of taking other small vertebrates as opportunities arose. Folded teeth appear not to be a rare phenomenon among parareptiles, but given the lack of detailed descriptions of the dentition for many parareptiles, the evolutionary history of polyplocodont teeth in this group requires further investigation. Phylogenetic analysis of an augmented data matrix from the literature supports the hypothesis of a sister-group relationship between C. pholeter and the lanthanosuchoid Acleistorhinus pteroticus.