A new study suggests that dinosaurs might have evolved more rapidly than we'd thought, emerging less than 5 million years after so-called "pre-dinosaurs" hit the scene. That shaves about 10 million years off the previous evolutionary time line.
The paper published Monday in the Proceedings of the National Academy of Sciences revisits the age of some important early dinosaur fossils.
The researchers, led by University of Buenos Aires paleontologist Claudia Marsicano, suggest that these vital fossils - found in the Chañares Formation in Argentina - have previously been misdated.
The Chañares is important because it features fossils from dinosaurs as well as dinosauromorphs from earlier in evolutionary history, so researchers can track their evolutionary time line.
These dinosauromorphs were generally on the small side, but otherwise quite similar to the dinosaurs we're all familiar with - with a few important exceptions. Most notably, the earlier creatures lacked the ball-and-socket hips of later dinosaurs. While they coexisted for millions of years, true dinosaurs would eventually outcompete their predecessors.
Inside the rocks of the Chañares, paleontologists can watch the whole thing go down.
"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," Marsicano said in a statement. "Because of this, the margin of error is very narrow because you can see the complete history all in one basin."
To get the most accurate dating for the rocks holding these fossils, Marsicano and her team took samples from the basin and crushed them to extract zircon crystals left behind by volcanic eruptions. They then measured the precise ratio of uranium to lead in the crystals. Because the uranium in these crystals decays into lead over time at a known rate, the researchers could date them exactly based on the ratio of the two elements.
And since the Chañares has been shown to be 5 million to 10 million years younger than previously thought, pre-dinosaurs have as well. That gives dinosaurs a lot less time to show up, but they managed it anyway.