Life would have been particularly hot and dry if dinosaurs really appeared near the equator
Mark Witton/Trustees of the Natural History Museum, London
Dinosaurs may have first evolved close to the equator, not in the southern part of the southern hemisphere as previously thought. A modeling study suggests that the original in a region covering what is the Amazon rainforest, the Congo basin and the Sahara desert.
“When you consider the gaps in the fossil record and the evolutionary tree of dinosaurs, it could very likely be a center of origin for dinosaurs,” says Joel Heath of University College London.
Dinosaurs evolved sometime during the Triassic period, which ran from 252 to 201 million years ago, but Heath says there is “pretty huge” uncertainty about where and when. The oldest known fossils of these animals are about 230 million years old, but they are different enough to suggest that dinosaurs had already been around for a few million years. “There must have been a lot going on in terms of dinosaur development, but we just don’t have the fossils,” he says.
At this time, Earth looked very different. All the continents joined together into a single supercontinent called Pangea, which was shaped like a C with its middle tightening at the equator. South America and Africa were in the southern hemisphere segment of this where they fit together like a puzzle. The earliest known dinosaurs are from southern parts of these two continents in places like Modern Argentina and Zimbabwe – so this was assumed to be their point of origin.
To learn more, Heath and his colleagues built computer models to work backwards in time from the oldest known dinosaurs to the group’s origins. They created several dozen versions, to account for AccountéTainties such as gaps in the fossil record, possible geographic barriers, and ongoing doubts about howling dinosaurs were related to each other.
Most of these simulations concluded that dinosaurs first appeared near the equator, with just a minority supporting a southern origin.
Palaeontologists have tended to assume that dinosaurs couldn’t have originated near the equator, Heath says, because there are no early dinosaur fossils from that region. In addition, it was a challenging place to live. “It was very, very dry and very hot,” he says. “The dinosaurs were thought to have been unable to survive in these spells.”
However, most of the models say otherwise. “It suggests things that we didn’t actually think were possible in the past,” says Heath.
Instead, the lack of early dinosaur fossils from near the equator may have a more prosaic explanation. Palaeontologists have tended to dig in North America and Europe and, more recently, China. “There are lots of areas in the world that are quite neglected,” says Heath. He adds that geologists have found rocks of the right age in the regions traveling to the study’s findings to excavate. “They may not be exhibiting in a way that we can easily study them.”
However, evidence has recently emerged to support Heath’s idea. On January 8, researchers led by David Lovelace at the University of Wisconsin-Madison reported that they had found the oldest known dinosaur from the northern part of Pangea. They discovered a species that is new to science called Ahvaytum Bahndooiveche, A sauropodomorph related to long-necked dinosaurs such as Diplodocus That developed later. The team found it in the rocks of the Popo Agie Formation in Wyoming, dated to 230 million years ago.
If dinosaurs were already in northern and southern Pangea that long ago, the equatorial center may not have been closed to them, says Heath. “They must have crossed that region.”
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