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Dinosaur Evolution: Chañares Formation Suggests Dinosaurs Evolved Rapidly From Ancestors

Dec 08, 2015 06:37 PM EST
Early Dinosaurs
The Chanares Formation in Argentina has preserved fossils of both dinosaurs and their predecessors, scientifically known as dinosauromorphs.
(Photo : Victor Leshyk)

Hidden in the 250-foot thick sediment pile-up that is Argentina's Chañares Formation, there is a treasure trove of dinosaur ancestry. Using the evolutionary secrets preserved in the many layers left behind by streams, rivers and lakes in the Triassic Period, researchers reveal dinosaurs may have evolved more rapidly than previously thought -- roughly five million years or less after their predecessors emerged.

Dinosauromorphs are considered the earliest relatives of dinosaurs.  For their study, researchers from Argentina, Brazil, California and the Natural History Museum of Utah at the University of Utah collected rock samples from the Chañares Formation and used radioactive isotope measurements to date zircon crystals left behind by volcanic eruptions that occurred when the sediments were originally deposited, according to a news release.

Volcanic ashes, or tuff, can be dated with great accuracy by measuring the ratio of uranium to lead in the crystals, simply because uranium decays into lead over time at a known rate. This revealed that the formation, and therefore the fossils found in it, is actually 234 to 236 million years old, from the Late Triassic Period. So, the formation had been misdated and is between five and 10 million years younger than previously thought.

"Among Triassic geologic formations containing fossils, the Chañares Formation is a classic. It contains a variety of complete fossil specimens of early dinosauromorphs, which are essentially dinosaur aunts, uncles and cousins," Randall Irmis, co-author of the study and an associate professor and curator of paleontology at the Natural History Museum, explained in the release. "To discover that these early dinosaur relatives were geologically much younger than previously thought was totally unexpected."

That is, the fact that the Chañares Formation contains fossils from both dinosaurs and dinosauromorphs allows researchers to basically trace the evolutionary timeline.  

"In other basins, dinosaur precursors, early dinosaurs and faunas dominated by dinosaurs do not all conveniently exist in the same place. In the basin containing the Chañares Formation, you can follow hundreds of meters of sediments back through time. Because of this, the margin of error is very narrow because you can see the complete history all in one basin," Claudia A. Marsicano, lead author of the recent study from the University of Buenos Aires, added.

Compared to the dinosaurs we are most familiar with, dinosauromorphs were smaller, and while they lived among dinosaurs for many years, increased competition eventually got the best them.

"For so long, people have been asking why did dinosaurs become so successful and what was special about them," Irmis told "This shows that dinosaurs were just a part of a bigger radiation of dinosauromorphs and we should be really asking the question why dinosaurmorphs became so successful."

Their findings were recently published in the Proceedings of the National Academy of Sciences

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

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