Fourth grade in Mrs. Allio’s class was when I first learned about dinosaurs. We learned the different types (for some reason, I favored the Brontosaurus) and what they ate, struggled to understand words like “Mesozoic” and “paleontology” and memorized the various theories for why the dinosaurs became extinct (had this happened gradually as temperatures grew warmer? as mammals developed and ate their eggs? Or had a massive meteor hit the earth and wiped the dinosaurs out?).
A new finding in the fossil record provides physical evidence for the latter theory. Scientists have found the the fossilized horn of a ceratopsian — most likely of a Triceratops — that must have lived before the catastrophic meteor impact 65 million years ago. The finding lends weight to the asteroid impact theory, as it suggests that dinosaurs did not slowly die out, but became extinct just prior to the impact.
The fossil was found in the Hell Creek formation in Montana, where other Triceratops fossils have been found. It was found just five inches below the Cretaceous-Tertiary (K–T) layer, which is the geological layer that marks the boundary from the Cretaceous period to the Tertiary period 65 million years ago, which is the time the mass extinction of dinosaurs is dated. The discovery suggests that something called the “three-meter gap” — which has been used to support the theory that dinosaurs died out slowly before the meteor impact — does not exist, as noted in Science Daily:
Since the impact hypothesis for the demise of the dinosaurs was first proposed more than 30 years ago, many scientists have come to believe the meteor caused the mass extinction and 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.)
As Yale graduate student Tyler Lyson, director of the Marmarth Research Foundation and lead author of the study, says,
“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.”
Lyson and his team at first thought the specimen was buried within the K-T boundary by about three feet. Analysis of soil samples helped them to identify the exact location of the boundary, based on a “relative abundance of certain types of fossilized pollen and other geological indicators but is difficult to determine visually while in the field.” Previously, scientists had relied on a visual examination of the actual rock formations in the field to determine the boundary’s location; the soil analysis provides for a more precise sense of where the boundary is. Lyson and his team are now using similar soil analysis to examine other specimens found close to the K-T boundary. He now “suspects that other fossils discovered in the past may have been closer to the boundary than originally thought and that the so-called three-meter gap never existed.”
Which would mean the non-avian dinosaurs did not go extinct prior to a meteor hitting the earth — or whatever happened 65 million years ago.
The study was published in the July 12 issue of Biology Letters.
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