DECAPODS (SHRIMP, LOBSTERS, AND CRABS) AND THEIR ROLE IN THE MESOZOIC MARINE REVOLUTION

Decapods have been implicated as one of the drivers of the Mesozoic Marine Revolution (MMR) for decades. Their crushing claws and shell-peeling ability have been anecdotally and systematically studied over that period of time. Examination of the time of appearance of well documented durophagous adaptations of various decapod lineages, including heterochely, molariform teeth on claws, and a curved proximal tooth on claws for shell peeling, shows that many of the adaptations presumed to have driven evolution during the MMR occurred late during that time. Crushing mandibles, flattened pereiopods for shell opening, and use of unspecialized appendages are other feeding mechanisms used by decapods that must also have exerted selective pressure on Mollusca as well as other lineages, although rarely discussed or tested in the MMR literature. Detailed examination of the fossil record of lobsters suggests that they may have played a role in the MMR, but it would have been through a variety of predatory means, as the claws of the Triassic and many Jurassic forms were small and slender or were pseudochelate. During the late Mesozoic lobsters exhibited a trend toward flattened, achelate forms, suggesting even more strongly that shell crushing by lobsters was not a strong evolutionary driver. In fact, extant lobsters inhabit environments to which they began to shift in the Late Cretaceous that may suggest movement to escape from other predators. These predators may have been bony fish and sharks, the former of which radiated in the Late Cretaceous (Friedman and Sallan, 2012). Modern achelate scyllarid and palinurid lobsters often live in reefs and rocky environments, hiding in crevices (Holthuis, 1991). Modern polychelids most often live in bathyal environments, away from the crowded, predator-dense shallow environments they seem to have preferred in the Mesozoic. These groups may have been victims as well as perpetrators of the MMR. This research was supported by NSF EAR-1223206 to Schweitzer and Feldmann and DEB EF‑0531670 to Feldmann and Schweitzer.