Back in school, we all learned about the mass extinction that killed the dinosaurs and ushered in the era of mammals. But what most of us don’t realise is that nearly 190 million years before the extinction of the dinosaurs was an even larger mass extinction event.
Called the Permian-Triassic extinction and dating back nearly 252 million years ago, it has the claim of being the Earth’s most severe known extinction event – serving as the end-of-the-road for 96 % of all marine species and 70 % of all terrestrial vertebrate species. It also has the distinction of being the only known mass extinction of insects. In fact, the Permian-Triassic extinction was so massive, it left 57 % of all biological families and 83 % of all genera extinct in its wake.
Despite its large-scale destruction, the Permian-Triassic extinction also ushered in one of the most important evolutionary diversifications ever. This includes the rise of the archosaurs, a general term that includes not only the now-extinct dinosaurs, but also crocodilians and birds – many of whose ancestors are still around. Even though they went on to dominate terrestrial ecosystems for over 130 million years – and still represent the most diverse group of land vertebrates today – little is known about the early evolution of archosaurs and their close relatives.
The EU-funded ARCHOSAUR RISE project has shed new light on this exciting corner of evolution. “A central goal of palaeontology and evolutionary biology is to understand the drivers and dynamics of the major evolutionary events that have shaped the history of life on Earth and governed the origins of today’s flora and fauna,” says researcher Richard Butler.
Butler and his team of researchers visited museum collections around the world to study fossil specimens of early archosaurs and collect data on their anatomy. They also carried out fieldwork in key rock sequences from the Triassic Period in South Africa and India, collecting new fossils of early archosaurs and the animals that lived alongside them.
“From this research, we have a much more detailed understanding of the patterns of how archosaurs and their relatives diversified and rose to dominance in the aftermath of the Permian-Triassic mass extinction,” says Butler. For example, researchers now recognise that much of this diversification took place 5 million years after the extinction, as global ecosystems finally began to stabilise and recover. “This has helped us better understand just how slow the recovery from mass extinctions can be,” adds Butler.
The project also provided critical new insights into the origins of dinosaurs, challenging traditional and long-established hypotheses about the morphology and evolution of the immediate ancestors and close relatives of the first dinosaurs. For example, in 2017, the project team was involved in describing a new species called Teleocrater, which was discovered in 245-million-year-old rocks in Tanzania.
“As the oldest known close relative of the dinosaur, Teleocrater challenges traditional hypotheses about dinosaur ancestors, which have reconstructed them as tiny, pigeon-sized animals running fast on two legs,” explains Butler. “Instead, Teleocrater is a much larger and slower moving, four-legged animal.”
Butler notes that Teleocrater was identified based on fossils at the Natural History Museum in London, which were collected in the 1930s, thus demonstrating the importance of re-evaluating museum collections.
Scratching the surface
Although the project has closed, Butler remains busy. For example, in the second half of 2018 he helped curate an exhibition entitled ‘Drawing Out the Dinosaurs’ at the University of Birmingham’s Lapworth Museum of Geology.
Butler also continues the research first started during the ARCHOSAUR RISE project, both in South Africa and Russia. “The insights we gained during the project were significant, but we really just scratched the surface,” he says. Thanks in part to the work done during the ARCHOSAUR RISE project, he received a collaborative research grant with scientists at Moscow’s Paleontological Institute. Together, they are currently examining in detail the Russian record of Early and Middle Triassic archosaurs.