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New sediment dating changes dinosaur timeline

The new dating data suggests many Middle-Triassic fossils may actually be Late Triassic.

By Brooks Hays
Dusk descends upon the badlands of the Chañares Formation in Argentina's Talampaya National Park. Geologists have re-dated sediments known for holding dinosaur fossils. Photo by study co-author Adriana Mancuso
Dusk descends upon the badlands of the Chañares Formation in Argentina's Talampaya National Park. Geologists have re-dated sediments known for holding dinosaur fossils. Photo by study co-author Adriana Mancuso

SALT LAKE CITY, Dec. 8 (UPI) -- Researchers at the University of Utah have been retesting the age of soil and rock strata well known for the fossils they house -- specifically, the remains of the earliest dinosaur relatives.

The new data, published in the journal PNAS, suggest the first dinosaur species and their earliest relatives, called dinosauromorphs, weren't separated by as large a chronological gap as previously thought.

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After analyzing zircon crystals from Argentina's Chanares Formation, scientists realized the sediments from which they have long been unearthing dino relatives are 234 to 236 million years old -- 5 to 10 million years younger than earlier estimates.

"To discover that these early dinosaur relatives were geologically much younger than previously thought was totally unexpected," Randall Irmis, associate professor and curator of paleontology at the Natural History Museum, said in a press release.

The Chanares Formation is offers one of the most complete fossil records on Earth, making it an ideal place to study the timeline of dinosaur evolution.

"If you wish to constrain a major evolutionary event, like the beginning of a group or the diversification of a group, the methodology has to have a margin of error that is much smaller," explained study author Claudia Marsicano, a University of Buenos Aires paleontologist.

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"For something that happens over the course of, say, 600 million years, an error of 3 to 4 million years is not statistically significant," she continued. "But if something happens over the course 10 to 12 million years, like the diversification of a group, an error of 3 to 4 million years is a major problem."

Now, for the first time, researchers have accurately dated the sediment layers containing dinosauromorphs. They did so by measuring the ratio of uranium to lead in resident zircon crystals.

As uranium decays, it becomes lead. And because uranium decays at a consistent rate, scientists use it to precisely measure the age of rocks.

The new dates suggest early dinosaurs evolved much more quickly than previously thought, but the findings may have larger implications than reshuffling the timeline of early dinosaur evolution. Geological formations key in the study of other fossil timelines may have to be re-dated.

Many Middle Triassic fossils may actually be Late Triassic.

"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.

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