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Permian–Triassic rocks of the Transantarctic Basin provide an unparalleled record of high latitude paleoenvironments and terrestrial vertebrate faunas. Here we summarize the taxonomic and paleoecological implications of the approximately 1300 vertebrate fossils collected since 1968, as well as report on new geologic field observations made during the 2017–18 austral field season. The Fremouw Formation records a vertebrate assemblage taxonomically most similar to that of the Karoo Basin of South Africa, with 10 genera shared in common. However, temnospondyls form a much greater percentage of tetrapod occurrences in the Fremouw Formation, suggesting favorable conditions for these ectothermic fossil amphibians at high latitudes. Lower Triassic small reptiles (viz. Procolophon, Prolacerta) occur in slightly higher proportions than in the Karoo, but their taxonomic diversity is likely undercounted. Seven stratigraphic columns of the upper Buckley and lower–middle Fremouw formations detail fluvial depositional environments in the central Transantarctic region, recording a shift from wet swamp lands to drier floodplains, most similar to Gondwanan basins in Australia. Fremouw Formation paleosols primarily consist of Protosols, which indicate poor soil forming conditions likely due to low precipitation and high sediment supply from crevasse splays. Mineralogy from X-ray diffraction, review of igneous intrusives, and Buckley Formation coal characterization demonstrate post-pedogenic diagenetic alteration that casts doubt on the results of previous stable isotopic studies of these paleosols. Tetrapod fossils first appear in the Fremouw Formation, which has been taken as evidence for immigration to the Antarctic portion of southern Pangea around the time of the end-Permian mass extinction. However, this may be due to higher soil pH, increased base saturation, lower moisture content, and more rapid burial conditions in the Fremouw than the underlying Buckley Formation that favored bone preservation.
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Africa’s oldest dinosaurs reveal early suppression of dinosaur distribution
The vertebrate lineages that would shape Mesozoic and Cenozoic terrestrial ecosystems originated across Triassic Pangaea1,2,3,4,5,6,7,8,9,10,11. By the Late Triassic (Carnian stage, ~235 million years ago), cosmopolitan ‘disaster faunas’ (refs. 12,13,14) had given way to highly endemic assemblages12,13 on the supercontinent. Testing the tempo and mode of the establishment of this endemism is challenging—there were few geographic barriers to dispersal across Pangaea during the Late Triassic. Instead, palaeolatitudinal climate belts, and not continental boundaries, are proposed to have controlled distribution15,16,17,18. During this time of high endemism, dinosaurs began to disperse and thus offer an opportunity to test the timing and drivers of this biogeographic pattern. Increased sampling can test this prediction: if dinosaurs initially dispersed under palaeolatitudinal-driven endemism, then an assemblage similar to those of South America4,19,20,21 and India19,22—including the earliest dinosaurs—should be present in Carnian deposits in south-central Africa. Here we report a new Carnian assemblage from Zimbabwe that includes Africa’s oldest definitive dinosaurs, including a nearly complete skeleton of the sauropodomorph Mbiresaurus raathi gen. et sp. nov. This assemblage resembles other dinosaur-bearing Carnian assemblages, suggesting that a similar vertebrate fauna ranged high-latitude austral Pangaea. The distribution of the first dinosaurs is correlated with palaeolatitude-linked climatic barriers, and dinosaurian dispersal to the rest of the supercontinent was delayed until these barriers relaxed, suggesting that climatic controls influenced the initial composition of the terrestrial faunas that persist to this day.
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- Award ID(s):
- 2010677
- PAR ID:
- 10520346
- Publisher / Repository:
- Springer Nature
- Date Published:
- Journal Name:
- Nature
- Volume:
- 609
- Issue:
- 7926
- ISSN:
- 0028-0836
- Page Range / eLocation ID:
- 313 to 319
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41586-022-05133-x
