Dinosaurs might be old, but their ancestors are actually a lot younger than previously thought.
Randy Irmis, associate professor of geology and curator of paleontology at the Natural History Museum of Utah, worked with researchers from Argentina, Brazil and California to study a rock formation known to contain many of the dinosaur relatives’ fossils. They dated the Chañares Formation, found in Argentina, at 234 to 236 million years old.
“This Chañares Formation, which has the early dinosauromorphs (think of them as the aunts, uncles and cousins of dinosaurs), is a lot later than we thought,” he said.
The fossils were previously dated at 240 to 245 million years ago. This places them a lot closer to the first dinosaurs, which were seen about 231 million years ago.
This geologic formation, which was discovered and named in the 1950s, is found in La Rioja Province in northwestern Argentina. It contains dinosaur precursors, such as the dicynodont Dinodontosaurus and the cynodont Massetognathus.
“If you want to study the origin and diversification of dinosaurs, this is the place to do it,” Irmis said.
Now that Irmis and his team have dated these formations, they will continue to study other geologic formations and see if they are in fact more recent. With current data, the Chañares Formation contains the first dinosaurs in the world, but Irmis hasn’t ruled out finding other older fossils.
The team used radio-isotopic techniques to study the minerals in the rock. They took rock samples that contained volcanic ash and crushed them to extract a mineral called zircon. Zircon incorporates uranium, which decays into uranium over time. By measuring the ratio of uranium to lead in the crystal, they can see how far back the crystal was formed and, therefore, how old the rock is.
Diego Fernandez, research associate professor of geology, said the radioisotopic technique researchers use to date the fossils (done by measuring the amount of uranium) is one of the best known ways to do so and is constantly improving.
“Techniques are evolving all the time,” he said. “Things nobody was doing three or five years ago, now they can do.”
Irmis has been working with this type of radioisotopic dating technology for years, and because of his experience, researchers from Argentina asked if he would join the team with Claudia Marsicano, Adriana Mancuso, Roland Mundil and Farid Chemale. Now, Irmis hopes others will follow suit and try to re-date common formations so scientists can come closer to understanding the animals that used to walk this earth.
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