Adam M. Yates

Solving a dinosaurian puzzle: the identity of Aliwalia rex Galton

Eucnemesaurus fortis Van Hoepen 1920 from the Late Triassic of South Africa is demonstrated to be the senior synonym of the puzzling dinosaur taxon Aliwalia rex Galton 1985. A new specimen of this poorly-known taxon is described. Eucnemesaurus is clearly a sauropodomorph and increases the diversity of sauropodomorph taxa in the South African Late Triassic to six. It shares a number of femoral synapomorphies with Riojasaurus from the Late Triassic of Argentina and Riojasauridae tax. nov. is erected to accommodate them. These conclusions are supported by a comprehensive cladistic analysis of 46 sauropodomorph and other basal dinosauriform taxa using 353 osteological characters. This analysis also supports the paraphyletic nature of the traditional ‘prosauropod’ assemblage.

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

Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow

Fossorialism is a beneficial adaptation for brooding, predator avoidance and protection from extreme climate. The abundance of fossilised burrow casts from the Early Triassic of southern Africa is viewed as a behavioural response by many tetrapods to the harsh conditions following the Permo-Triassic mass-extinction event. However, scarcity of vertebrate remains associated with these burrows leaves many ecological questions unanswered. Synchrotron scanning of a lithified burrow cast from the Early Triassic of the Karoo unveiled a unique mixed-species association: an injured temnospondyl amphibian (Broomistega) that sheltered in a burrow occupied by an aestivating therapsid (Thrinaxodon). The discovery of this rare rhinesuchid represents the first occurrence in the fossil record of a temnospondyl in a burrow. The amphibian skeleton shows signs of a crushing trauma with partially healed fractures on several consecutive ribs. The presence of a relatively large intruder in what is interpreted to be a Thrinaxodon burrow implies that the therapsid tolerated the amphibian’s presence. Among possible explanations for such unlikely cohabitation, Thrinaxodon aestivation is most plausible, an interpretation supported by the numerous Thrinaxodon specimens fossilised in curled-up postures. Recent advances in synchrotron imaging have enabled visualization of the contents of burrow casts, thus providing a novel tool to elucidate not only anatomy but also ecology and biology of ancient tetrapods.

The Early Evolution of Postcranial Skeletal Pneumaticity in Sauropodomorph Dinosaurs

Postcranial skeletal pneumaticity (PSP) is present in a range of basal sauropodomorphs spanning the basal sauropodomorph—sauropod transition. We describe the PSP of five taxa, Plateosaurus engelhardti, Eucnemesaurus fortis, Aardonyx celestae, Antetonitrus ingenipes, and an unnamed basal sauropod from Spion Kop, South Africa (hereafter referred to as the Spion Kop sauropod). The PSP of Plateosaurus is apparently sporadic in its occurrence and has only been observed in very few specimens, in which it is of very limited extent, affecting only the posterior cervical vertebrae and possibly the mid dorsals in one specimen. The PSP of Eucnemesaurus, Aardonyx, Antetonitrus, and the Spion Kop sauropod consists of subfossae (fossa-within-fossa structures) that excavate the vertices of the posterior infradiapophyseal fossae of the posterior dorsal vertebrae. These subfossae range from simple shallow depressions (Eucnemesaurus) to deep, steepsided, internally subdivided and asymmetrically developed chambers (Antetonitrus). The middle and anterior dorsal vertebrae of these taxa lack PSP, demonstrating that abdominal air sacs were the source of the invasive diverticula. The presence of pneumatic features within the infradiapophyseal fossae suggest that the homologous fossae of more basal saurischians and dinosauriforms were receptacles that housed pneumatic diverticula. We suggest that it is probable that rigid non-compliant lungs ventilated by compliant posterior air sacs evolved prior to the origination of Dinosauria.

A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph-sauropod boundary?

The early evolution of sauropod dinosaurs remains poorly understood, with a paucity of unequivocal sauropod taxa known from the first twenty million years of the Jurassic. Recently, the Early Jurassic of South Africa has yielded an assemblage of dental and post-cranial remains displaying a more apomorphic character suite than any other similarly aged sauropodomorph. These remains are interpreted as a new species of basal sauropod and recovered cladistically as the sister taxon to Vulcanodon +more derived Sauropoda, underscoring its importance for our understanding of this pivotal period of sauropod evolution. Key changes in the dentition, axial skeleton and forelimb of this new species suggest a genuine functional distinction occurring at the sauropodiform-sauropod boundary. With reference to these changes, we propose a scenario in which interdependent refinements of the locomotory and feeding apparatus occurred in tandem with, or were effected by, restrictions in the amount of vertical forage initially available to the earliest sauropods. The hypothesized instance of niche-partitioning between basal sauropodan taxa and higher-browsing non-sauropodan sauropodomorphs may partially explain the rarity of true sauropods in the basal rocks of the Jurassic, while having the added corollary of couching the origins of Sauropoda in terms of an ecologically delimited ‘event’.

A Second Species of Eucnemesaurus Van Hoepen, 1920 (Dinosauria, Sauropodomorpha): New Information on the Diversity and Evolution of the Sauropodomorph Fauna of South Africa's Lower Elliot Formation (Latest Triassic)

ABSTRACT The Late Triassic—Early Jurassic Elliot Formation of South Africa is one of the most important geological formations worldwide for understanding the early evolution of sauropodomorph dinosaurs. However, many of the taxa currently recognized as valid within its lower strata remain either poorly understood, vaguely diagnosed, or both. The recent discovery of an articulated partial skeleton of a single individual of the enigmatic lower Elliot genus Eucnemesaurus provides an important opportunity to expand our understanding of the anatomy and phylogeny of this poorly known taxon. A comprehensive investigation of the morphological relationships of this new specimen identified key features, pertaining primarily to the femoral shaft and distal tibia, which distinguish it from the only other previously named species of Eucnemesaurus—E. fortis. A new species, E. entaxonis, is erected within which to accommodate it. A cladistic analysis confirms the monophyly of Eucnemesaurus, as well as its continued inclusion within the low-diversity ‘Riojasauridae.’ Nonetheless, this result highlights continued uncertainties regarding the constituency of the Riojasaurus hypodigm. The relatively robust pedal architecture of E. entaxonis suggests an unexpectedly early experiment in a slower, subgraviportal form of locomotion within Late Triassic basal Massopoda, whereas the intriguing mosaic of plesiomorphic and derived characters evident in E. entaxonis raises questions regarding the hypothesized population dynamics of the basal-most sauropodomorph taxa of the lower Elliot Formation. This latter concern has particular bearing on newly observed inconsistencies in the prevailing hypodigms of other lower Elliot basal sauropodomorph taxa such as Melanorosaurus.

A pathological tail in a basal sauropodomorph dinosaur from South Africa: evidence of traumatic amputation?

RICHARD J. BUTLER,*,1 ADAMM. YATES,2,3 OLIVERW. M. RAUHUT,1,4 and CHRISTIAN FOTH4; 1GeoBio-Center, Ludwig-Maximilians-Universitat Munchen, Richard-Wagner-Strase 10, D-80333 Munich, Germany, r.butler@lrz.uni-muenchen.de; 2Bernard Price Institute, University of the Witwatersrand, Johannesburg 2050, South Africa; 3Museum of Central Australia, Araluen Cultural Precinct, P.O. Box 3521, Alice Springs, Northern Territory 0871, Australia; 4Bayerische Staatssammlung fur Palaontologie und Geologie and Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitat Munchen, Richard-Wagner-Strase 10, D-80333 Munich, Germany

Sexual dimorphism in the late Miocene mihirung Dromornis stirtoni (Aves: Dromornithidae) from the Alcoota Local Fauna of central Australia

ABSTRACT The dromornithids were giant flightless birds endemic to Australia from the late Paleogene to the late Pleistocene. Dromornithids are generally considered to be divergent members of the Anseriformes, but they display many convergent features with extant ratites. In this study, we investigate Dromornis stirtoni from the Alcoota Local Fauna, a species for which little is known of its biology. We used traditional methods of comparative morphology, mass estimation, landmark-based morphometrics, and histological investigations to determine the presence of medullary bone, to assess the possible presence, form, and extent of sexual dimorphism in D. stirtoni. Two morphological groups were identified for each main leg element, differing primarily in relative robustness. Core samples from femora and tibiotarsi shafts revealed medullary bone in the less robust morph, indicating that these were females. Mass, as estimated by algorithms applied to our preferred measurement of least-shaft circumference of tibiotarsi, was significantly different between males (mean = 528 kg) and females (mean = 451 kg). Therefore, male D. stirtoni were more robust but not much taller than the females and challenge the elephant bird, Aepyornis maximus, for the title of the most massive bird to have existed. Sexual dimorphism in this largest of all dromornithids, therefore, was like that of extant Anseriformes. We infer long-term monogamy, mutual display, shared parental care, female incubation, and aggressive defense of nests in these birds. The techniques of geometric morphometrics applied in this study maximize the use of fragmentary material, helping to overcome the common paleontological challenge of limited sample sizes.

The Earliest Post-Paleozoic Freshwater Bivalves Preserved in Coprolites from the Karoo Basin, South Africa

Background Several clades of bivalve molluscs have invaded freshwaters at various times throughout Phanerozoic history. The most successful freshwater clade in the modern world is the Unionoida. Unionoids arose in the Triassic Period, sometime after the major extinction event at the End-Permian boundary and are now widely distributed across all continents except Antarctica. Until now, no freshwater bivalves of any kind were known to exist in the Early Triassic. Principal Findings Here we report on a faunule of two small freshwater bivalve species preserved in vertebrate coprolites from the Olenekian (Lower Triassic) of the Burgersdorp Formation of the Karoo Basin, South Africa. Positive identification of these bivalves is not possible due to the limited material. Nevertheless they do show similarities with Unionoida although they fall below the size range of extant unionoids. Phylogenetic analysis is not possible with such limited material and consequently the assignment remains somewhat speculative. Conclusions Bivalve molluscs re-invaded freshwaters soon after the End-Permian extinction event, during the earliest part of the recovery phase during the Olenekian Stage of the Early Triassic. If the specimens do represent unionoids then these Early Triassic examples may be an example of the Lilliput effect. Since the oldest incontrovertible freshwater unionoids are also from sub-Saharan Africa, it is possible that this subcontinent hosted the initial freshwater radiation of the Unionoida. This find also demonstrates the importance of coprolites as microenvironments of exceptional preservation that contain fossils of organisms that would otherwise have left no trace.

What Lies Beneath: Sub-Articular Long Bone Shape Scaling in Eutherian Mammals and Saurischian Dinosaurs Suggests Different Locomotor Adaptations for Gigantism

Eutherian mammals and saurischian dinosaurs both evolved lineages of huge terrestrial herbivores. Although significantly more saurischian dinosaurs were giants than eutherians, the long bones of both taxa scale similarly and suggest that locomotion was dynamically similar. However, articular cartilage is thin in eutherian mammals but thick in saurischian dinosaurs, differences that could have contributed to, or limited, how frequently gigantism evolved. Therefore, we tested the hypothesis that sub-articular bone, which supports the articular cartilage, changes shape in different ways between terrestrial mammals and dinosaurs with increasing size. Our sample consisted of giant mammal and reptile taxa (i.e., elephants, rhinos, sauropods) plus erect and non-erect outgroups with thin and thick articular cartilage. Our results show that eutherian mammal sub-articular shape becomes narrow with well-defined surface features as size increases. In contrast, this region in saurischian dinosaurs expands and remains gently convex with increasing size. Similar trends were observed in non-erect outgroup taxa (monotremes, alligators), showing that the trends we report are posture-independent. These differences support our hypothesis that sub-articular shape scales differently between eutherian mammals and saurischian dinosaurs. Our results show that articular cartilage thickness and sub-articular shape are correlated. In mammals, joints become ever more congruent and thinner with increasing size, whereas archosaur joints remained both congruent and thick, especially in sauropods. We suggest that gigantism occurs less frequently in mammals, in part, because joints composed of thin articular cartilage can only become so congruent before stress cannot be effectively alleviated. In contrast, frequent gigantism in saurischian dinosaurs may be explained, in part, by joints with thick articular cartilage that can deform across large areas with increasing load.