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Alice Springs, Australia

Bonnan M.F.,The Richard Stockton College of New Jersey | Wilhite D.R.,Auburn University | Masters S.L.,Beaumont School | Yates A.M.,Museum of Central Australia | And 3 more authors.

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. © 2013 Bonnan et al. Source

Mcphee B.W.,University of Witwatersrand | Yates A.M.,Museum of Central Australia | Choiniere J.N.,University of Witwatersrand | Abdala F.,University of Witwatersrand
Zoological Journal of the Linnean Society

We present a comprehensive description and phylogenetic analysis of the important transitional sauropodomorph Antetonitrus ingenipes. New information sheds light on the stepwise acquisition of sauropod-like traits just prior to the Triassic/Jurassic boundary. Although the forelimb of Antetonitrus and other closely related sauropodomorph taxa retains the plesiomorphic morphology typical of a mobile grasping structure, the changes in the weight-bearing dynamics of both the musculature and the architecture of the hindlimb document the progressive shift towards a sauropodan form of graviportal locomotion. Nonetheless, the presence of hypertrophied muscle attachment sites in the femur of Antetonitrus suggests the retention of an intermediary form of facultative bipedalism. The term Sauropodiformes is adopted here and given a novel definition intended to capture those transitional sauropodomorph taxa occupying a contiguous position on the pectinate line towards Sauropoda. A re-examination of the biased distribution of Sauropodomorpha in the earliest Jurassic suggests the presence of genuine palaeo-environmental processes that may have excluded the large-bodied, graviportal taxa from participating in a number of Early Jurassic ecosystems. © 2014 The Linnean Society of London. Source

Worthy, T.H. & Yates, A., 27.3.2015. Connecting the thigh and foot: resolving the association of post-cranial elements in the species of Ilbandornis (Aves: Dromornithidae). Alcheringa 39, xxx–xxx. ISSN 0311-5518 Fossils of the two mid-sized dromornithid species classified in Ilbandornis are re-examined. A study of the large series of fossils from the late Miocene (ca 9–7 Ma) Alcoota Local Fauna shows that the holotypes of Ilbandornis woodburnei Rich and Ilbandornis lawsoni Rich, a femur and a tarsometatarsus, respectively, pertain to separate taxa. However, the femora and tibiotarsi of these species have been confused in the past. We provide qualitative descriptions and morphometrics to discriminate the limb bones, which overlap in absolute size. Ilbandornis woodburnei is characterized by short tarsometatarsi, tibiotarsi with relatively broad distal ends, and femora with a broad sulcus patellaris. In contrast, I. lawsoni has very elongate tarsometatarsi, slender tibiotarsi with relatively narrow distal ends, and femora with a narrow sulcus patellaris. Two morphotypes of the proximal pedal phalanges are present in the Alcoota LF. These manifest overlapping length ranges but are distinguished by relative robustness and other details of shape. For each phalanx II.1, III.1 and IV.1, those referred to I. lawsoni are more slender than those referred to I. woodburnei, with, for example, the trochlea articularis of II.1 and the proximal width of III.1 as a proportion of length, both more transversely compressed. Examination of the dromornithids from the middle Miocene Bullock Creek Local Fauna (ca 15–12 Ma), previously referred to? Bullockornis sp., and the late Miocene Ongeva LF (ca 7–6 Ma) reveals that two species of Ilbandornis are present in each fauna. On available data, these are indistinguishable from I. lawsoni and I. woodburnei, attesting to the continuity of these lineages minimally from 12 Ma to 7 Ma in parallel with a Dromornis lineage. Trevor H. Worthy [trevor.worthy@flinders.edu.au], School of Biological Sciences, Flinders University, GPO 2100, Adelaide 5001, SA, Australia; Adam Yates [adamm.yates@nt.gov.au], Museum of Central Australia, PO Box 831, Alice Springs, Northern Territory 0871, Australia. © 2015 Association of Australasian Palaeontologists. Source

Megirian D.,Museum of Central Australia | Prideaux G.J.,Flinders University | Murray P.F.,Museum of Central Australia | Smit N.,Marine Biodiversity Group

Constrained seriation of a species-locality matrix of the Australian Cenozoic mammal record resolves a preliminary sixfold succession of land mammal ages apparently spanning the late Oligocene to the present. The applied conditions of local chronostratigraphic succession and inferences of relative stage-of-evolution biochronology lead to the expression of a continental geological timescale consisting of, from the base, the Etadunnan, Wipajirian, Camfieldian, Waitean, Tirarian, and Naracoortean land mammal ages. Approximately 99 of the 360 fossil assemblages analyzed are classifiable using this method. Each is characterized by a diagnostic suite of species. An interval of age magnitude may eventually be shown to lie between the Camfieldian and Waitean, but is currently insufficiently represented by fossils to diagnose. Development of a land mammal age framework marks a progressive step in Australian vertebrate biochronology, previously expressed only in terms of local faunas. Overall, however, the record remains poorly calibrated to the Standard Chronostratigraphic Scale. Codifying the empirical record as a land mammal age sequence provides an objective basis for expressing faunal succession without resort to standard chronostratigraphic terms with the attendant (and hitherto commonly taken) risks of miscorrelating poorly dated Australian events to well-dated global events. © 2010 The Paleontological Society. All rights reserved. Source

New jaws and teeth referable to the rare thylacoleonid marsupialWakaleo alcootaensis are figured and described. The species is the geologically youngest known member of the genus and is only known from the late Miocene Alcoota Local Fauna of the Northern Territory, Australia. A revised diagnosis of the species is presented which is found to be morphologically distinct from its congeners. W. alcootaensis can be distinguished from other species of Wakaleo by its greater size, deeply recessed masseteric fossa, more steeply angled I1, loss of P2, greater P3 to M1 ratio and loss of M3. Several characters of W. alcootaensis, including the increase in size, steeply angled I1, increase of the relative size of P3, and reduction of the molar row are present in at least some species of Thylacoleo. Phylogenetic analysis suggests that these character states are convergences and that there was parallel evolution in these two thylacoleonid lineages. © 2015 Yates. Source

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