The classic dinosaur family tree could be inacurrate

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The classic dinosaur family tree has two subdivisions of early dinosaurs at its base: the Ornithischians, or bird-hipped dinosaurs, which include the later Triceratops and Stegosaurus; and the Saurischians, or lizard-hipped dinosaurs, such as Brontosaurus and Tyrannosaurus.

Now an MIT geochronologist, along with paleontologists from Argentina and Brazil, has found evidence to support the classical view of dinosaur evolution.

The team reanalyzed fossils of Pisanosaurus, a small bipedal dinosaur that is thought to be the earliest preserved Ornithiscian in the fossil record. The researchers determined that the bird-hipped herbivore dates back to 229 million years ago, which is also around the time that the earliest lizard-hipped Saurischians are thought to have appeared.

The new timing suggests that Ornithiscians and Saurischians first appeared and diverged from a common ancestor at roughly the same time, giving support to the classical view of dinosaur evolution.

“For many years, people thought Chinle and Ischigualasto formations didn’t overlap, and based on that assumption, they developed a model of diachronous evolution, meaning the earliest dinosaurs appeared in South America first, then spread out to other parts of the world including North America,” Ramezani says. “We’ve now studied both formations extensively, and shown that diachronous evolution isn’t really based on sound geology.”

Source: https://www.heritagedaily.com/2020/07/study-sheds-light-on-the-evolution-of-the-earliest-dinosaurs/134491

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