230 million-year-old fossils from Zimbabwe reveal the secret origin of dinosaurs in Pangaea

“The Triassic Period saw the origin of most of the major groups of land vertebrates (lizards, dinosaurs, mammals, etc.). We hope that this hypothesis-driven method, using climate and biogeography to conduct targeted paleontological fieldwork, will be useful for studying the origins of these major groups as they arose across Pangaea,” said Griffin.

Although, at present, there are vast geographical barriers such as oceans and mountains that affect species distribution, climate and different climate zones still play an important role in the dispersal of fauna. Various studies highlight that the evolution and distribution of animals in a region are mostly driven by climatic conditions. The most obvious and current example is the drastic change in species distribution happening across the globe due to climate change.

For instance, research from the U.S. Department of Agriculture suggests that the rate of migration observed in insects, birds, and tree species is witnessing a major shift, but even this rate is not enough to cope with the threats that climate change poses.

Coming back to the recent study, Griffin and his team are planning to excavate more sites in Zimbabwe. “The biggest limitation (of our research) is simply that the fossil record is incomplete. New finds can overturn old hypotheses, but this is just a better reason to keep looking,” Griffin told IE.

The study is published in the journal Nature.

Abstract:

The vertebrate lineages that would shape Mesozoic and Cenozoic terrestrial ecosystems originated across Triassic Pangaea1–11. By the Late Triassic (Carnian stage, ~235 million years ago), cosmopolitan ‘disaster faunas’ (refs. 12–14) 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 distribution15–18. 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 America4,19–21 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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