Ross Damiani

Earliest evidence of cynodont burrowing

A 251 million year old partial burrow cast containing an articulated skeleton of the mammal–like carnivore Thrinaxodon liorhinus is the oldest evidence for burrowing by a cynodont synapsid. The burrow cast comes from terrestrial flood plain sediments close to the Permian–Triassic boundary in the Karoo of South Africa. Together with those of the later cynodont Trirachodon, the Thrinaxodon burrow cast indicates that burrow–making was broadly distributed in basal synapsids and has a long history in non–mammalian synapsid evolution. A reconstruction of its appendicular skeleton in cross–section indicates that Thrinaxodon was able to adopt a facultatively mammalian stance within its burrow shaft. Burrows of cynodont design are more common in Triassic rocks than previously realized, and suggest that burrowing may represent an adaptive response by cynodonts to the environmental conditions associated with the mass extinction event that punctuated the end of the preceding Permian period. The widespread occurrence of burrowing among extant mammals implies that the ancient synapsid ability to burrow conferred a strong adaptive value in the evolution of Mammalia.

A procolophonoid reptile with temporal fenestration from the Middle Triassic of Brazil

The small tetrapod Candelaria barbouri, from the Middle Triassic of southern Brazil, is the first example of an owenettid procolophonoid outside Africa and Madagascar. Candelaria barbouri was originally described as a primitive procolophonid; however, a re–examination of the holotype, as well as new material, reveals that C. barbouri is in fact the youngest member of the Owenettidae, extending the chronological range of the group by more than 10 million years. The recognition of C. barbouri as an owenettid points to a broader diversity and distribution for owenettids than hitherto thought. In addition, C. barbouri is the first member of the Owenettidae to exhibit temporal fenestrae, a discovery that draws attention to the significance of this feature in ‘anapsid’ reptiles.

A new Triassic procolophonoid reptile and its implications for procolophonoid survivorship during the Permo-Triassic extinction event.

A reptile specimen from the Lystrosaurus Assemblage Zone of the Beaufort Group, lowermost Triassic of South Africa, represents a new procolophonoid parareptile. Sauropareion anoplus gen. et sp. nov. is identified as the sister taxon of Procolophonidae in a phylogenetic analysis of procolophonoids. Stratigraphic calibration of the most parsimonious tree reveals that four of the six procolophonoid lineages originating in the Permian Period extended into the succeeding Triassic Period. This relatively high taxic survivorship (67%) across the Permo–Triassic boundary strongly suggests that procolophonoids were little if at all affected by the mass extinction event that punctuated the end of the Palaeozoic Era (ca. 251 million years ago).

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

THE VERTEBRATE FAUNA OF THE UPPER PERMIAN OF NIGER. IV. NIGERPETON RICQLESI (TEMNOSPONDYLI: COCHLEOSAURIDAE), AND THE EDOPOID COLONIZATION OF GONDWANA

Abstract We describe the edopoid temnospondyl Nigerpeton ricqlesi from the Upper Permian Moradi Formation of northern Niger on the basis of two partial skulls and tentatively associated postcranial material. This crocodile-like taxon displays several edopoid characters states such as a long prenarial region with enlarged premaxillae, elongated vomers, large, posteriorly tapering choanae, and a jugal that broadens anteriorly. Nigerpeton possesses a unique carnivo rous dentition. It is autapomorphic in its possession of an extremely elongate snout bearing a maxillary bulge that accommodates three hypertrophied caniniform teeth, inner premaxillary tusks, and anterior paired fenestrae, which pierce the skull roof. In addition, both the maxilla and dentary tooth rows show the sporadic appearance of ‘doubled’ tooth positions. The lateral-line system is present at the adult stage, which suggests an aquatic habitat for this taxon. A phylogenetic analysis of Edopoidea and its relatives places Nigerpeton as the sister taxon to the Permo-Carboniferous genus Chenoprosopus from the U.S.A. As with other members of the Moradi tetrapod fauna, the discovery of Nigerpeton strengthens support for the hypothesis that West Africa hosted an endemic fauna at the close of the Paleozoic Era. Biogeographically, we propose that Late Carboniferous and Permian edopoids were geographically widespread and that they twice crossed the Central Pangean mountain chain (between Laurussia and Gondwana) during their evolution. This distribution was later fragmented with the onset of Late Permian climatic warming.

First trematosaurid temnospondyl from the Lystrosaurus Assemblage Zone of South Africa and its biostratigraphic implications

A large temnospondyl mandible from the Lystrosaurus Assemblage Zone (Early Triassic) of South Africa is referred to the higher-level taxon Trematosauridae. The mandible is remarkably similar to that described for Trematosaurus from the Middle Buntsandstein of Germany, a genus closely related to the South African Trematosuchus , for which the mandible is unknown. However, the mandible cannot be referred unequivocally to either of these taxa. Trematosuchus is considered to be restricted to the lowermost subzone of the overlying Cynognathus Assemblage Zone, which, based principally on the temnospondyl and therapsid fauna, is considered to be of Upper Olenekian age. The mandible described here extends back the range of the Trematosauridae to the underlying Lystrosaurus Assemblage Zone and argues against the long-held notion of a sharp palaeontological break between the faunas of the Lystrosaurus and Cynognathus Assemblage zones. It also supports the hypothesis that the Lystrosaurus Assemblage Zone extended up to the Upper Olenekian.

Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy

Abstract The Permo-Triassic Beaufort Group (Karoo Basin) of South Africa is biostratigraphically subdivided into eight, temporally successive assemblage zones based on therapsids (‘mammal-like reptiles’). The Temnospondyli, fossil tetrapods usually regarded as extinct amphibians, are second only to therapsids in terms of diversity and abundance in these strata, with nine higher-level taxa (‘families’) known. Temnospondyls are also playing an increasingly important role in biostratigraphy and correlation of the Beaufort strata. The lower Beaufort Group (Late Permian) contains six of the eight biozones, but only one temnospondyl ‘family’, the Rhinesuchidae, whose record in the Karoo is the richest in the world. However, rhinesuchid taxonomy remains in flux and the group is thus of limited biostratigraphic utility. The Early Triassic Lystrosaurus Assemblage Zone (middle Beaufort Group) contains the Rhinesuchidae, Amphibamidae, Lydekkerinidae, Tupilakosauridae, Rhytidosteidae, Mastodonsauridae and Trematosauridae, although the biostratigraphy of temnospondyls within this biozone is poorly constrained. The uppermost reaches of the Lystrosaurus biozone contain a paucity of fossils but includes ‘Kestrosaurus’ (Mastodonsauridae) and ?Trematosuchus (Trematosauridae), taxa previously thought to pertain to the lower part of the overlying Cynognathus biozone. The late Early to Middle Triassic Cynognathus Assemblage Zone (upper Beaufort Group) hosts the Mastodonsauridae, Trematosauridae, Brachyopidae, Laidleriidae and, possibly, the Rhytidosteidae. Based largely on the spatial and temporal distribution of mastodonsaurids, this biozone has been biostratigraphically subdivided into a lower A, middle B and upper C subzones, characterised by differing ages and faunas.

A Reappraisal Of Coletta Seca, A Basal Procolophonoid Reptile From The Lower Triassic Of South Africa

The skeletal structure of Coletta seca, a small procolophonoid reptile from the Lower Triassic Lystrosaurus Assemblage Zone of South Africa, is reconsidered in light of descriptions of other procolophonoids. The presence of a single row of relatively large, fang–like vomerine teeth, identified originally as the single autapomorphy of this taxon, is reinterpreted as two rows of parachoanal vomerine teeth that are similar in organization to those of coeval procolophonids from Russia. Coletta is distinguished from other procolophonoids by a complex tongue–and–groove suture between the anterolateral margin of the parietal and the posterolateral edge of the postfrontal, and by a transversely broad interpterygoid vacuity. The postfrontal in Coletta retains contact with the postorbital, as in basal taxa such as Owenetta, but it is restricted to the orbital margin, as in Procolophon and all other procolophonids. A phylogenetic analysis identifies Coletta as the sister taxon of the clade Procolophonidae. This phylogenetic position suggests that Procolophonoidea originated and diversified initially in Gondwana during the Permian, prior to Procolophonidae achieving a cosmopolitan distribution in the succeeding Triassic.

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.

New mastodonsaurid temnospondyls from the Cynognathus Assemblage Zone (Upper Beaufort Group; Karoo Basin) of South Africa

Abstract Two new mastodonsaurid temnospondyls are described from the Early to Middle Triassic Cynognathus Assemblage Zone of the Upper Beaufort Group (Karoo Basin) of South Africa. Paracyclotosaurus morganorum, sp. nov. is based on a partial skull from the uppermost part of the Cynognathus Assemblage Zone (Subzone C; late Anisian) in the southern Karoo Basin, and is the first occurrence of the genus Paracyclotosaurus outside of India and Australia. Jammerbergia formops, gen. et sp. nov. is based on a partial skull, presumably from Subzone B (early Anisian) of the Cynognathus Assemblage Zone, and is distinctive in its unique suite of primitive and derived characters. Although the intrarelationships of mastodonsaurids remain largely unresolved, the two most recent analyses are similar in the identification of an ‘advanced’ mastodonsaurid clade whose members are characterized by laterally directed tabular horns. Jammerbergia probably belongs within this clade, albeit within a basal position. Jammerbergia and Paracyclotosaurus share the synapomorphy of large, antero-posteriorly expanded tabulars, and may represent sister taxa. The Cynognathus Assemblage Zone is characterized by three subzones of differing ages and faunas, with no overlap in the temnospondyls between the subzones.