Scientists have announced that prehistoric animals thought to be distant relatives of dinosaurs were actually much closer to them on the family tree.
The research team comprised paleontologists from Brazil, Argentina and the U.S. The Natural History Museum of Utah led the U.S. side of the research, helping to date fossil specimens from a site where a volcano once erupted in what is now Argentina. That site is called the Chañares Formation, and it is famous for its fossils of early dinosaur relatives, called dinosauromorphs.
Dinosauromorphs aren't direct ancestors of dinosaurs, but are "aunts, uncles and cousins," as Randall Irmis put it. Irmis is the curator of paleontology at the Natural History Museum and a co-author of the study.
The team used radioactive isotope measurements to date the sediment in which the fossils were buried. In particular, zircon crystals (made famous by cubic zirconia, considered a cheaper version of a diamond), held the secret to accurately dating the fossils.
The team found that the volcanic grave and all its fossils are 234 to 236 million years old, placing them in the late Triassic Period. Previous estimates had these fossils five to 10 million years older than that. Thus, they were the same number of years closer to the animals we commonly refer to as dinosaurs.
"To discover that these early dinosaur relatives were geologically much younger than previously thought was totally unexpected," said Irmis.
Knowing the accurate date also changes our view of the landscape on which these animals roamed. The Chañares Formation, now high desert badlands, were a lush and tropical home to the dinosauromorphs, and the atmosphere was extremely CO2-rich. These findings will give more clues to the physiology of the animals who called our Earth home even before the dinosaurs did.
The results of the research were recently published in the Proceedings of the National Academy of Sciences, and made available online this week.