Argentina’s Talampaya National Park is a desert expanse. Spanning 830 square miles, the area is characterized by craggy badlands with sparing vegetation. For paleontologists the site is specifically rich as it’s home to the Chañares Formation, a 250 ft thick geologic formation made of sediments from ancient waterways. According to the United Nations, the park along with the neighboring Ischigualasto National Park boast the most complete continental fossil record from the Triassic Period.
But a new study published in Proceedings of the National Academy of Sciences is calling into question the geologic timeline between dinosaurs and dinosauromorphs, early relatives of the former.
“Among Triassic geologic formations containing fossils, the Chañares Formation is a classic,” said the study’s coauthor Randall Irmis, a professor and curator at the Univ. of Utah’s National History Museum. “It contains a variety of complete fossil specimens of early dinosauromorphs, which are essentially dinosaur aunts, uncles and cousins.”
The team measured radiocarbon isotopes extracted from zircon crystals found within volcanic ash in the formation. The crystals contained uranium, which over time decayed into lead. Using a mass spectrometer, they measured the uranium/lead ratio in each crystal.
“The Chañares Formation contains tuffs, or volcanic ash, that can be dated with great accuracy,” said the study’s lead author Claudia A. Marsicano, of the Univ. of Buenos Aires. “So in this basin, not only are there many high-quality, complete fossils that allow us to easily identify taxa, but there are also tuffs in between that allow us to date the entire column.”
The results indicate the formation’s base is no older than 236 million years, and the top layer, no older than 235 million years. That is 5 to 10 million years younger than the previous estimate for the Middle Triassic period, indicating the time period between dinosauromorphs and dinosaurs is much shorter than previously believed.
“We always thought these ‘Middle Triassic’ fossils showed the ecological recovery from the worst mass extinction of all time, the end-Permian extinction, but if these fossils are actually Late Triassic in age, they really have nothing to do with that recovery,” said Irmis.
According to the Univ. of Utah, the new research calls into question the geologic timelines of formations bearing fossil species similar to the Chañares Formation, including the Maria Formation in Brazil and the Karoo sequence in South Africa.