Yale Graduate School of Arts and Sciences

Graduate School News and Events

In Search of the Last Dinosaur

A team of scientists, including graduate students Tyler Lyson (Geology & Geophysics) and Stephen Chester (Anthropology), has discovered the remains of the youngest dinosaur ever found. The location of their finding strongly suggests that dinosaurs did not go extinct prior to the catastrophic meteor impact that struck the earth 65 million years ago and gives further evidence that the impact was in fact the cause of their extinction.

The fossilized horn of a ceratopsian — probably a Triceratops — was found last year in the Hell Creek badlands in Montana, a barren, rugged area. The fossil was buried just five inches below what is known as “the K-T boundary,” the geological layer that marks the transition from the Cretaceous period to the Tertiary period. Eric Sargis, curator of vertebrate paleontology at the Yale Peabody Museum of Natural History, and Stephen Chester discovered the ceratopsian while searching for fossilized mammals that evolved after the meteor impact. At first the team thought the fossil was buried within about three feet of the K-T boundary, but was surprised to learn just how close to the boundary it was indeed buried — and hence, how close in time to the meteor’s impact. Because the dinosaur was buried in a mudstone floodplain, they knew it had not been re-deposited from older sediments, which can sometimes happen when fossils are found in riverbeds that may have eroded and re-distributed their material over time. They sent soil samples to a laboratory to determine the exact location of the boundary, which is marked by the relative abundance of certain types of fossilized pollen and other geological indicators that are difficult to determine visually while in the field.

Last dinosaur workers

Looking for dinosaurs in Rwanda

Since the impact hypothesis for the demise of the dinosaurs was first proposed more than 30 years ago, many scientists have come to believe that a meteor wiped out the dinosaurs, but a sticking point has been an apparent lack of fossils buried within the 10 feet of rock below the K-T boundary. The seeming anomaly has come to be known as the “three-meter gap.” Until now, this gap has caused some paleontologists to question whether the non-avian dinosaurs of the era — which included Tyrannosaurus rex, Triceratops, Torosaurus and the duckbilled dinosaurs – gradually went extinct sometime before the meteor struck. Avian dinosaurs survived the impact, and eventually gave rise to modern-day birds.

“This discovery suggests the three-meter gap doesn’t exist,” said Tyler, director of the Marmarth Research Foundation and lead author of the study, which was published in July in the journal Biology Letters. The Foundation, which Tyler started while an undergraduate at Swarthmore College, is a non-profit organization devoted to public education, scientific research and curation of fossils. Some of their finds have been featured in a National Geographic documentary and a Kingfisher Publications children’s book. Tyler grew up in Marmarth in southwestern North Dakota — right in the middle of the Hell Creek formation. “I was interested in vertebrate paleontology starting at a young age. In fact I began working for various professors as a full time summer job when I was 12, and I’ve been doing it ever since.”

The team is now examining other fossil specimens that appear to be buried close to the K-T boundary and expect to find more. “The fact that this specimen was so close to the boundary indicates that at least some dinosaurs were doing fine right up until the impact.” While the exact age of the fossil cannot be determined, Tyler says, “This discovery provides some evidence that dinosaurs didn’t slowly die out before the meteor struck.”

Tyler’s dissertation research, advised by Jacques Gauthier, focuses on the origin of turtles, integrating fossil, morphological, molecular, and developmental data to figure out what group of animals they are most closely related to: birds and crocodiles, lizards, or the “clade” made up of lizards, birds and crocodiles. He also studies the origin of the turtle shell. Tyler has been digging in the Hell Creek region’s “Turtle Graveyard,” the world’s most important fossil turtle site, for the past nine years.

Tyler Lyson