Dinosaur Roots Discovered in Africa: Fossils Reveal Origins After Mass Extinction

First Posted: Apr 30, 2013 08:06 AM EDT

Where are the roots of the dinosaur family tree? Good question. Many scientists once believed that dinosaur predecessors missed the race to fill habitats when nine out of 10 species disappeared during Earth's largest mass extinction event about 252 million years ago. Yet now, they've discovered new fossils that may reveal a lineage of dinosaurs that appeared after this extinction event and preceded other dinosaurs in the fossil record.

The new findings were located in Tanzania and Zambia and have been dated back to the mid-Triassic period, which is millions of years before dinosaur relatives were seen in the fossil record elsewhere on Earth. It wasn't easy tracking down these fossils, though. It took seven fossil-hunting expeditions since 2003 in Tanzania, Zambia and Antarctica and work combing through existing fossil collections before researchers made their findings.

In order to better understand the history of these dinosaurs, the researchers created two "snapshots" of four-legged animals about five million years before and again about 10 million years after the extinction even at the end of the Permian period.

"The fossil record from the Karoo of South Africa remains a good representation of four-legged land animals across southern Pangea before the extinction event," said Christian Sidor, University of Washington professor of biology, in a news release. "But after the event, animals weren't as uniformly and widely distributed as before."

In fact, prior to the extinction even the pig-sized Dicynodon was a dominant plant-eating species across southern Pangea. Looking a bit like a fat lizard with a short tail and a turtle's head, this creature disappeared during the mass extinction event. This, in turn, allowed newly emerging herbivores to be able to compete for food sources, and thus changed the whole dynamic of Earth's ancient ecosystem.

So what did the snapshot reveal? About 10 million years after the extinction event, archosaurs were in Tanzanian and Zambian basins, but not distributed across all of southern Pangea as had been the pattern for four-legged animals prior to the extinction. Archosaurs are a group of reptiles that include crocodiles, dinosaurs, birds and a variety of extinct creatures. They're thought to have eventually evolved into creatures such as Asilisaurus, a dinosaur-like animal, and Nyasasaurus parringtoni, a dog-like creature with a five-foot tail. Nyasasaurus in particular is thought to be one of the earliest dinosaurs in existence--or at least one of the dinosaurs' closest relatives.

In addition to these snapshots, researchers discovered that before the extinction event, about 35 percent of four-legged species were found in two or more of the five areas that were studied. Some species had ranges that stretched almost 1,600 miles and encompassed the Tanzanian and South American basins. Yet all that changed after the extinction event; the species began to cluster together, and just seven percent of species were found in two or more regions.

What does this mean for the dinosaurs? It reveals their origins and how they may have evolved after this extinction event. In addition, it shows their distribution across ancient Earth and allows us to understand a little bit more about our planet's history.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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