Newly discovered fossils from 10 million years after the world's largest known extinction indicate that dinosaurs' ancestors might have taken hold in present-day Tanzania and Zambia, millions of years before the dinosaurs roamed the Earth, and much earlier than dinosaur relatives are seen in the fossil record elsewhere, according to a new study in Proceedings of the National Academy of Sciences..
About 252 million years ago, 90 percent of marine life and about 70 percent of land animals vanished during what's known as the Permian-Triassic extinction event. No one knows why this happened, LiveScience.com reports. Scientists have speculated that meteorite impacts are a plausible explanation because they could have escalated volcanic activity and the release of carbon dioxide and methane, causing such major climate changes that many species may not have been able to survive..
The new study states that, “Bizarre four-legged creatures that resembled demonic dogs and predated the animals later called dinosaurs branched out shortly after an extinction that wiped out most of life on land.”. Some of these creatures were the direct ancestors of dinosaurs, and the mass extinction appears to have allowed them to flourish in spots in current-day Tanzania and Zambia.
"We get the hint that the dinosaur radiation, which we don't really see in the fossil record until about 20 million years later, is really starting to take off in this region," said Christian Sidor, a biologist at the University of Washington and a research associate at the Field Museum of Natural History in Chicago.
Researchers had thought that dinosaurs' predecessors hadn’t acted quickly enough to fill in the empty ecological niches left after their former occupants were wiped out, because that's what the fossil record seemed to show -- particularly in spots like South Africa's Karoo basin, which was treated as a sort of record of species in southern Pangaea (the super-continent that once contained nearly all the Earth’s landmass).
But now, it turns out that South Africa may not have been the right place to look. When the international team of scientists conducted a thorough search of fossil sites in Tanzania, Zambia and Antarctica and existing fossil collections, they found that the species that survived after the Great Dying were far more fragmentary and isolated than before the event.
Five million years before the extinction, 35% of four-legged species lived in at least two of five studied locations. But 10 million years afterward, only 7% did.
No longer could some species range a full 1,600 miles, as they did before the Great Dying. Different species were adjusting to dramatic environmental changes in their own local pockets of land. South Africa could no longer be a record for the larger region.
"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." [The 10 Weirdest Animal Discoveries]
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,” he mused.
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.
The researchers report their findings this week in the journal Proceedings of the National Academy of Sciences.