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

200 million years ago, there was no Asia, Europe, Africa, or North America. There existed only one supercontinent called Pangaea, and it was home to the earliest dinosaurs known to mankind.

A recently published study from Yale University highlights the role of different climate zones in the origin and distribution of early dinosaurs throughout Pangaea.

The authors of the study examined a collection of dinosaur fossils discovered in Zimbabwe. They believe that the fossils are 230 million years old and they belong to the earliest known Triassic-era dinosaur species of Africa, South America, and Asia. The fossils reveal important details about how dinosaurs and then later amphibians, mammals, and reptiles got dispersed across Pangaea.

How did climate belts affect the distribution of dinosaurs on Pangaea?

Currently, there are seven separate continents with numerous geographical barriers affecting the distribution of organisms across the globe. Explaining this further, lead researcher and postdoctoral fellow at Yale University, Christopher Griffin told IE, “We have geographical barriers to dispersal from continent to continent. The most obvious of these are the oceans, but extremely tall mountain ranges can also be geographic barriers to dispersal. These barriers, especially the oceans, were not factors in Pangaea.”

The authors believe that the distribution of early dinosaurs was largely affected by climate barriers instead of geographical ones. For instance, the fossil collection from Zimbabwe indicates that the earliest dinosaurs were exclusively from environments that were temperate and semi-arid to semi-humid regions in the south of Pangaea.

Griffin reveals that the fossils belong to Africa’s oldest known dinosaurs, and they are roughly the same age as the oldest dinosaurs found anywhere in the world. Surprisingly, the collection also comprises remains of early dinosaurs similar to those that existed in Central Africa, South America, and India. This indicates that the dinosaurs did not start out with a worldwide range but were restricted to only a part of southern Pangaea at the earliest part of their history.

Climate belts still affect the distribution of species

The researchers suggest that since the dispersal of the first dinosaurs was linked to climate barriers, for a long time, those gigantic animals remained confined to the climate zones that suited them, and they didn’t spread throughout Pangaea. Interestingly, it also affected the distribution of other animals that originated during the same era, including those that still exist to this date.

“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.