The Extinction Debate

There has been much debate about the extinction of the giant dinosaurs: Was it a catastrophic event caused by a meteorite? A gradual extinction caused by global warming? Or something else?
Proponents of the “catastrophic meteorite” hypothesis argue that dinosaurs were very diverse to the very end of the Cretaceous Period. Those who argued for the “gradual” hypothesis proposed that the large dinosaurs were dwindling by the end of the Cretaceous, or even that they were already extinct. A so-called three meter gap—a zone of rock representing the end of the Cretaceous that seemed to have no vertebrate fossils—seemed to support the gradual hypothesis. However, in 2010 Yale anthropology graduate student Stephen Chester found a dinosaur brow horn at Camel Butte that helped to fill this gap. The discovery showed that at least some dinosaurs were not extinct before the K–T boundary, but were alive and well right up to the end of the Mesozoic Era.

Photograph above:
This brow horn, from either Triceratops or Torosaurus, represents one of the last giant dinosaurs to roam Earth before these animals became extinct.

Screenwashing efforts at Camel Butte allow the recovery of microvertebrate fossils, like this tiny mammal tooth.

Our understanding of the recovery of mammals in the earliest Tertiary has been limited, because we have very few K–T boundary fossil sites. Camel Butte contains fossils of mammals and other vertebrates very close to the K–T boundary, probably from within the first 100,000 years after the extinction event. Yale paleontologists have collected more than 150 mammal fossils at Camel Butte, including several nearly complete jaw fragments from condylarths and multi-tuberculates, hundreds of other vertebrate fossils (including crocodiles, turtles and fish) and at least one new species of condylarth. Future expeditions and ongoing research will bring more insights about the evolution of mammals and other vertebrates after the Age of Dinosaurs.

Photograph Above:

Yale Geology and Geophysics graduate student Tyler Lyson carefully excavates the brow horn core and collects rock samples (right) to be analyzed back at the lab to determine the exact placement of the K-T boundary.