EVOLUTIONARY AND ENVIRONMENTAL TRENDS IN BODY SIZE OF DECAPOD CRUSTACEANS DURING THE MESOZOIC

The biodiversity of decapod crustaceans increased by three orders of magnitude during the Mesozoic. New groups common in today’s oceans such as Brachyura and Anomura first appeared and radiated during that time, whereas groups of Paleozoic origin (lobsters and shrimp) diversified. Our current understanding of this Mesozoic Decapod Revolution remains mostly qualitative. In particular, quantitative documentation of evolutionary trends in decapod body size, both within and across environments, is lacking. This hampers our understanding of the ecological role and long-term evolution of decapods during this time interval when these crustaceans established themselves as a major faunal component of marine ecosystems. We have assembled body size estimates for ~750 marine brachyuran and lobster species, the two groups best represented in the Mesozoic fossil record of decapods. Both groups seem to increase in median species length throughout the Mesozoic. Furthermore, crab length increased faster in non-reef habitats than in reef habitats so that Cretaceous reef crabs seem smaller than those found in other environments, perhaps highlighting the importance of environmental determinants during the evolutionary history of decapods. The long-term increase in decapod body size coupled with their increased diversity throughout the Mesozoic may mean that the impact of these crustaceans on their environment changed.