George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing ''Tempo and Mode in Evolution'' (1944), ''The Meaning of Evolution'' (1949) and ''The Major Features of Evolution'' (1953). He was an expert on extinctmammals and their intercontinental migrations. Simpson was extraordinarily knowledgeable about Mesozoic fossil mammals and fossil mammals of North and South America. He anticipated such concepts as punctuated equilibrium (in ''Tempo and Mode'') and dispelled the myth that the evolution of the horse was a linear process culminating in the modern ''Equus caballus''. He coined the word ''hypodigm'' in 1940, and published extensively on the taxonomy of fossil and extant mammals. Simpson was influentially, and incorrectly, opposed to Alfred Wegener's theory of continental drift, but accepted the theory of plate tectonics (and continental drift) when the evidence became conclusive.