The pig-size Dicynodon was part of a large, dominant group of plant eaters found across the southern hemisphere until the mass extinction event weakened their numbers so that newly emerging herbivores could compete. (Photo : Marlene Donnelly/Field Museum of Natural History/ University of Washington )
Researchers have now found that dinosaur-like creatures were living in Tanzania and Zambia before they were found anywhere else on the Earth. These ancestors of dinosaurs lived in the mid-Triassic period.
Previous studies, mostly on fossils obtained from South Africa and southwest Russia, had led researchers to believe that the predecessors of dinosaurs failed to repopulate Earth after a mass extinction some 252 million years ago.
"The fossil record from the Karoo of South Africa, for example, is a good representation of four-legged land animals across southern Pangea before the extinction," says Christian Sidor, a paleontologist at the University of Washington.
Pangea was a landmass that had all continents. The Southern Pangea was comprised of present-day regions such as Africa, South America, Australia and Antarctica.
The latest study is based on fossils obtained from non-traditional sites like Tanzania, Zambia and Antarctica. The expeditions were funded by the National Science Foundation (NSF).
Researchers created a kind of snapshot, based on the available fossil records, of the creatures that roamed the Earth some 5 million years before and 10 million years after the event.
Some types of four-legged creatures lost the race after the mass extinction, such as the Dicynodon- a creature that had the head of a turtle with the body of a fat lizard. Dicynodon along with its relative disappeared after the massive wipeout of dinosaurs more than 250 million years ago.
"Groups that did well before the extinction didn't necessarily do well afterward," Sidor added, according to a news release.
In the second snapshot, archosaurs were present in the Tanzanian basin but weren't found in other places. This four-legged animal is of great interest to researchers because it is believed to be a predecessor of dinosaurs and a relative of crocodiles.
The study showed that animals were widespread before the mass extinction event. But, even 10 million years after the event, only 7 percent of the animals were found in two or more places, showing that there was geographical clustering of animals.
The study is published in the journal Proceedings of the National Academy of Science.
