CEB Committe on Evolutionary Biology

Spotlight : David Grossnickle

David Grossnickle

David Grossnickle in Montana with a T. rex skull that’s been wrapped in a protective plaster cast.

I am interested in the origin and evolutionary history of mammals during the Mesozoic Era (i.e., the Age of Dinosaurs), which is a geologic span of time from 250 to 66 million years ago (mya). This period encompasses the first two thirds of mammalian history. Traditionally, early mammals were described as small, nocturnal insectivores that managed to survive past the demise of non-avian dinosaurs, subsequently radiating into the wide breadth of ecological niches they now occupy. However, incredible fossil discoveries over the past 20 years have upturned this view and demonstrate that Mesozoic mammals achieved surprising ecological, morphological, and taxonomic diversity before the extinction of dinosaurs. Thus, these study organisms offer a unique opportunity to make considerable contributions to our understanding of mammalian origins and early history.

To examine whether mammals were ecologically and morphologically ‘suppressed’ during the Age of Dinosaurs, one of my recent research projects examines macroevolutionary patterns of therian mammals prior to and immediately after the Cretaceous-Paleogene (K-Pg) mass extinction event 66 mya, which claimed non-avian dinosaurs. This project required photographing and analyzing the shapes of hundreds of fossil molars, which are especially informative because their morphology is often indicative of dietary preference. Results suggest that therian mammals were experiencing an evolutionary radiation prior to the K-Pg extinction event. In addition, Paleogene results suggest that the extinction event preferentially claimed dietary specialists, and mammals may have experienced a longer post-extinction recovery period than previously recognized. The major implication of these results is that early mammalian history may have been less correlated with the presence or absence of non-avian dinosaurs than previously thought. Other ecological factors, such as the rise of flowering plants during the Late Cretaceous, may have had a greater effect on mammalian history. (For more information on the project, see

CEB has been considerably supportive of my research. The program encourages development of independent and integrative research projects. Further, travel and grant funding (e.g. Hinds Fund for Graduate Research) has allowed me to visit several museums for data collection, as well as travel to multiple conferences to present my work. Thus, I greatly appreciate the opportunities that CEB has provided.

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