Palaeontologist and professor in the Department of the Geophysical Sciences of the University of Chicago. His research emphasises combining data from living and fossil organisms to study the origins and fates of lineages and adaptations, to develop an understanding of the underlying dynamics of speciation and extinction that could lead to a general theory of evolutionary novelty. He is interested in the way evolutionary patterns are shaped by the alternation of extinction regimes, with rare but influential mass extinctions driving unexpected evoutionary shifts.