"After the extinction, things change dramatically," Sidor said. "The animals that are common in the Karoo are not the ones that are common in Tanzania."
In particular, Sidor said, the post-extinction landscape hosted many archosaurs, a group that includes crocodiles, birds, flying reptiles called pterosaurs and non-avian dinosaurs. An animal that may be the earliest known dinosaur, or at least the archosaur most closely related to dinosaurs — Nyasasaurus parringtoni—comes from Tanzania and lived about 245 million to 240 million years ago.
"There are a whole bunch of different archosaurs," Sidor said. "There were plant-eaters, large carnivores, armored forms — so they were really taking off into a variety of different body forms. It's not just the origin of dinosaurs we're tracing backwards, but seemingly a completely different ecosystem in Tanzania than what you see in South Africa."
It's not clear how two similar ecosystems could emerge to be so different after a mass extinction, Sidor said, but it's not an uncommon occurrence. He likened the change to politics: It's hard to dislodge an incumbent politician, but once you do, anyone could step in to fill the gap.
Some scientists believe that the Earth is now undergoing another mass extinction, due to human activity. If this is the case, Sidor said, the Permian extinction is a cautionary tale.
"Mass extinctions have unpredictable consequences," he said. "You couldn't tell, based on what was existing before the extinction, what's going to do well afterwards."
The researchers report their findings this week in the journal Proceedings of the National Academy of Sciences.
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