Scientists previously thought that dinosaurs evolved from their smaller ancestors over a period of at least 10 million years but findings of a new study suggest that the evolution occurred in less than five million years.

For the new study published in the Proceedings of the National Academy of Sciences on Dec. 7, Randall Irmis, from the Natural History Museum, and colleagues used radioactive isotope measurements for dating the zircon crystals that were found in the sediments of the Chañares Formation, which is known for its fossils of early dinosaur relatives.

The analysis revealed that the formation is between 234 million and 236 million years old from the Late Triassic period, which means that the fossils of the dinosaur's reptile predecessors, the early dinosauromorphs, that were sandwiched in the rock layers are of the same age.

The early dinosauromorphs were like the dinosaurs sans some key features such as the former having a ball-and-socket hip that rotates easily and an additional vertebra at the end of their spine.

Scientists have already studied dinosauromorphs but there were uncertainties about their age since biostratigraphy, the technique used to date their fossils, were not as accurate as other dating methods such as the one employed in the new study.

The findings provided evidence that the early dinosauromorphs lived between five to 10 million years earlier than previously believed revamping the long held timeline of the early dinosauromorphs evolving into dinosaurs. The study likewise offered proof that the dinosaurs evolved much faster than previously thought.

"We constrain the rate of dinosaur origins, demonstrating their relatively rapid origin in a less than 5-Ma interval, thus halving the temporal gap between assemblages containing only dinosaur precursors and those with early dinosaurs," Irmis and colleagues wrote.

The researchers said that although the dinosaurs may have evolved rapidly, the prehistoric animals appear to have dominated paleo-Earth in a smooth and gradual manner. It took quite a while for the prehistoric giants to spread globally as it took them millions of year after their origin to gradually dominate the mid to high-latitude regions of the Earth.

"You don't seem to see dinosaurs showing up and immediately taking over," Irmis said. "It really emphasizes that there wasn't much special about the first dinosaurs. They were pretty similar to their early dinosauromorph relatives and probably doing very similar things."

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