Sixty-five million years ago, a giant asteroid collided with Earth. But were dinosaurs around when it hit?
A team of Yale scientists led by Tyler Lyson GRD ’12 and Stephen Chester GRD ’12 discovered a fossil last year that provides evidences for the well-known hypothesis that an asteroid wiped out the dinosaurs. They found the fossil only 13 centimeters below the layer of rock that indicates a massive impact 65 million years ago, a discovery that they said proves dinosaurs were thriving before an asteroid hit earth then.
Lyson and Chester found their fossil, likely a triceratops’ horn, in mudstone, as opposed to the usual sandstone, meaning that the fossils were untouched by relocating forces like river water.
Prior to their research, published in the July issue of the journal Biology Letters, a gap in the fossil record was believed to extend down 3 meters from the K-T boundary, which is a layer of rock containing fallout from the impact that is supposed to have killed the dinosaurs. The gap resulted from a lack of discovered in situ fossils, or remains preserved in their original location.
After a laboratory analysis, the team learned earlier this year that their in situ fossil dated just before the impact event, Lyson said.
“A colleague in France analyzed the pollen in the sample and it turned out that it was right below the K-T boundary,” Lyson said. “It was such exciting news. I wrote up the paper on a flight home.”
Since elementary school, Lyson has been hunting fossils at Hell Creek Formation, the same site in Montana where his team made their recent discovery. He oversaw the team’s reptile excavations, while Chester was in charge of the dig for mammals. It was Chester, an anthropology student, who initially unearthed the specimen.
The new in situ fossil complements the other fossils found below the K-T boundary, and weakens the arguments against the asteroid-extinction hypothesis, Lyson said. Warren Douglas Allmon, a paleontology professor at Cornell University, said this type of evidence, which expands the fossil record, is especially important to paleontologists.
“The authors can say we’ve established with much higher confidence that the last appearances of the dinosaurs were around the K-T boundary,” he said.
Since paleontologists rely on random geological conditions like river formations to make observations about ancient life, improving the range of bones available to study is an especially important job, Allmon added.
Lyson began working with a paleontologist in sixth grade, and in high school uncovered a “dino-mummy,” so-called because the dinosaur’s skin and muscles were still intact. That discovery earned him an interview on “Good Morning America.”
“Some of my earliest childhood memories are of looking for fossils,” Lyson said.
For decades, opponents of the asteroid-extinction hypothesis have cited the so-called “3-meter gap,” which refers to the apparent absence of fossilized dinosaurs below the K-T boundary, to show that dinosaurs died off before the impact, said Peter Sheehan, head of the Milwaukee Public Museum’s geology department.
“The initial thought in 1980 was that we never find fossils within the top three meters below the boundary,” he said. “That held up for a little while, but then people started finding fossils in that area; then it became, ‘Well, you’ll find some there, but they’re not common.’”
The new finding has convinced some scientists of the presence of dinosaurs up until the impact, although many remain skeptical, Lyson said.
“There have been people saying, ‘You’re wrong,’” he said. “That’s how science works.”