A new study by a team of scientists from Argentina, Brazil, California and the Natural History Museum of Utah at the University of Utah has determined that the time elapsed between the emergence of early dinosaur relatives and the origin of the first dinosaurs is much shorter than previously believed. The discovery not only places a new timeline on the connection between early dinosaur relatives and the first dinosaurs in this particular geologic formation, but also in other formations across the world. The team, which included Randall Irmis, associate professor and curator of paleontology at the Natural History Museum, employed radioactive isotope measurements to date zircon crystals found in the sediments of the Chañares Formation, which is famous for its fossils of early dinosaur relatives.

The team found that the formation, and therefore the fossils found in it, is 234 to 236 million years old, from the Late Triassic Period; this is 5-10 million years younger than previous estimate of a Middle Triassic age.

"To discover that these early dinosaur relatives were geologically much younger than previously thought was totally unexpected," said Irmis.

The results were recently published in the Proceedings of the National Academy of Sciences. The lead author is Claudia A. Marsicano from the University of Buenos Aires, and the co-authors are Irmis, Adriana C. Mancuso, Roland Mundil and Farid Chemale.