Abstract

New crayfish fossil evidence and plate tectonic configurations suggest that the fossil record of terrestrial and freshwater crayfish extends to the Late Pennsylvanian and points to their origin in the Early Carboniferous during the formation of the supercontinent Pangea (350-320 million years ago). Major ecological and environmental changes in the Carboniferous may have caused the migration of the crayfish ancestor into freshwater environments in the Laurasian tropics of Pangea. Based on burrow evidence in the Late Pennsylvanian and Early Permian, the ancestral stock gave rise to the Astacidae, members of which gave rise to the Cambaridae. By the Triassic (245 Ma), these families had diversified into nearly every alluvial and lacustrine environment in Laurasia. Prior to the separation of Pangea during the Late Triassic-early Jurassic, astacid stocks dispersed into Gondwana via migration along inland waterways. The break-up of Pangea and the isolation of Gondwana allowed the astacid stocks to give rise to the Parastacidae. The present distribution reflects the relict populations of these events and the genetic isolation and interspecific competition through time. Thus the Northern (Astacoidea) and Southern (Parastacoidea) Hemisphere crayfish families are the result of complex interplay between invasion, dispersal, isolation, and diversification concomitant with the dynamic tectonic history of the formation, separation, and dispersal of the continental elements of Pangea. Fossil crayfish anatomy, burrow architecture, and burrow depth reflect adaptations to habitat, oxygen saturation, and seasonal water-table fluctuations, which have remained unchanged for nearly 280 million years. The relative stasis in overall crayfish morphology and behavior suggests that change is unnecessary once an adaptable and successful life strategy is obtained.

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