Stephen Chester, an assistant professor of anthropology and paleontologist from Brooklyn College and The Graduate Center from The City University of New York, was a key collaborator in a groundbreaking discovery that reveals in striking detail how the world and life recovered after the asteroid impact that wiped out the dinosaurs 66 million years ago.

In short, while the catastrophic event closed the door to dinosaurs, it sprung it wide open for mammals—and eventually humans—to grow into the dominant species we know today. The unprecedented find includes thousands of exceptionally preserved animal and plant fossils from the critical first million years after the catastrophe. It was unearthed by a team of scientists in Colorado Springs, Colo., and it shines a revelatory light on how life emerged from Earth’s darkest hour.

Chester, who specializes in the early evolutionary history of primates and other placental mammals, was instrumental in a peer-reviewed scientific paper in the recent issue of Science magazine (pdf). The discovery will also be highlighted in a NOVA Documentary, Rise of the Mammals, streaming on PBS and airing Oct. 30.

Specifically, Chester and his colleagues identified fossil mammal species, calculated their body mass based on measurements of their skulls and teeth, and documented aspects of their anatomy to reconstruct behaviors such as their diets during the first million years after dinosaur extinction.

“This discovery unearthed complete skulls of many of these extinct mammals for the first time,” Chester said. “What makes this find even more amazing is that we also have many exceptionally preserved plant fossils that allow us to place these early mammals in an ecological context at a very high resolution through time. There are clear patterns linked with plants as mammals increased their species diversity and body mass rather quickly throughout the first million years after the mass extinction event. This discovery has produced a lifetime’s worth of fossils to work on, which will continue to provide us with a clearer view of the beginning of the age of mammals.”

This new and exceptional record from the first million years after the asteroid impact combines plants, animals and precise dates—a paleontological trifecta—painting a portrait of the emergence of the modern world.

Chester said overall, the study provides a better understanding of how life on Earth recovers following a mass extinction event, which has major and timely implications given that we are currently facing what many scientists call the sixth mass extinction today.

Dr. Tyler Lyson, the Denver Museum of Nature & Science’s curator of vertebrate paleontology and lead author of the Science magazine paper, and Dr. Ian Miller, the Museum’s curator of paleobotany and director of earth and space sciences, led the team that announced the discovery.

In addition to the paper published in Science magazine, the story of the discovery is told in a new documentary, Rise of the Mammals, a NOVA production by HHMI Tangled Bank Studios for WGBH Boston, that will stream online beginning today at across PBS platforms and mobile apps and will broadcast nationally on PBS Oct. 30 at 9 p.m. EDT.

“The course of life on Earth changed radically on a single day 66 million years ago,” said Lyson. “Blasting our planet, an asteroid triggered the extinction of three of every four kinds of living organisms. While it was a really bad time for life on Earth, some things survived, including some of our earliest, earliest ancestors.”

Collaborators included:

  • David Krause, James Hagadorn, Antoine Bercovici, Farley Fleming, Ken Weissenburger, Denver Museum of Nature & Science
  • Stephen Chester, Brooklyn College and The Graduate Center, The City University of New York (CUNY)
  • William Clyde and Anthony Fuentes, University of New Hampshire
  • Greg Wilson, University of Washington
  • Kirk Johnson and Rich Barclay, National Museum of Natural History, Smithsonian Institution
  • Matthew Butrim, Wesleyan University
  • Gussie Maccracken, University of Maryland
  • Ben Lloyd, Colorado College

For more information about NOVA Rise of the Mammals airing Oct. 30 at 9 p.m. EDT, please visit:

Photos and the paper that appears in Science magazine can be accessed through this Dropbox link here:

About Stephen Chester

Stephen Chester (Ph.D. Anthropology, Yale University, 2013) is a paleontologist who specializes in the origin and early evolutionary history of primates and other mammals. He is an assistant professor of anthropology at Brooklyn College and The Graduate Center of The City University of New York, and serves as an associate editor for the Journal of Human Evolution. Chester is affiliated with and builds fossil collections for the American Museum of Natural History, the Denver Museum of Nature & Science, the Florida Museum of Natural History, and the Yale Peabody Museum of Natural History. He is best known for his co-discovery of Purgatorius ankle bones which demonstrated that our earliest primate relatives were living in the trees shortly after the extinction of the dinosaurs.