Traditionally, the dinosaur family tree features to main subdivisions of the early dinosaurs at its base. The Ornithischians group features bird-hipped dinosaurs, with notable species being the Triceratops and Stegosaurs. Saurischians, which have lizard hips, are best known in the form of the Brontosaurus and Tyrannosaurs.
While this view has many supporters, it was challenged in 2017 when new information suggested that lizard-hipped dinosaurs were the first to evolve with the discovery forcing a series of major shifts in the branches of dinosaurs family trees.
A surprising discovery
A mixed team of researchers from MIT, Argentina, and Brazil have discovered new evidence in favor of the classical view on dinosaur evolution. The researchers reanalyzed a set of fossils of Pisanosaurus, which is deemed to be the earliest preserved Ornithiscian that is known at this point and concluded that the fossils could be traced back to 229 million years ago.
Within the same timeframe, the earlier Saurichians may have appeared. As such, the new timeline infers that both Ornithiscians and Saurichians have a common ancestor and have diverged at the same time, a theory that is in favor of the classical view of dinosaur evolution.
Extracting information from ancient rocks
During the study, researchers also took a closer look at a set of rocks collected from the Ischigualasto Formation, which is a layered sedimentary rock unit that is located in Argentina. The formation is well-known for the abundant presence of relics.
Fossils from the middle layers of the Chinle Formation, located in the U.S., was also of interest for the researchers as the period during which the Chinle and the Ischigualasto formations started to form is quite similar. However, it is interesting that the lower layers of the Chinle Formation do not feature a large number of fossils of any kind.
The new study has been published in a peer-reviewed journal.