CENOZOIC INTER-TIDAL, SUPRA-TIDAL, AND FRESHWATER CRABS FROM TROPICAL AMERICA

The transition from fully aquatic to terrestrial/semi-terrestrial habitats is an infrequent event in most plant and animal groups. This might be due to the considerable physical differences between air and water, physiological constraints, being outcompeted by previously established residents, and being exposed to new predators. Higher crabs, or Eubrachyura, are one of the few marine groups that have successfully invaded land and freshwater, although relatively recently in geological time. Unfortunately, the fossil record of terrestrial, semi-terrestrial, and freshwater crabs is very fragmentary, and usually represented by a handful of incomplete specimens. This is principally due to the unlikely preservation of suitable habitats in the geological record (mechanical bias), the geochemistry of their substrates preventing fossilization (chemical bias), and re–working or ingestion of their molts and corpses (biological bias). The discovery of three fossiliferous localities in Panamá and Colombia (Early Miocene to Holo–Pleistocene) has yielded a large collection of freshwater, supra-tidal, and inter-tidal crabs, including the land crab Cardisoma crassum (family Gecarcinidae), the ‘Sally Lightfoot’ crab Grapsus grapsus (family Grapsidae), hundreds of articulated adult and juvenile specimens of the heavy-clawed fiddler crab Uca ornata (family Ocypodidae), and some of the oldest —and one of the most complete yet known— fossil freshwater crabs (families Pseudothelphusidae and Trichodactylidae). Furthermore, we review the fossil record of fiddler crabs worldwide, and the phylogenetic relationships between the fossil and extant species of fiddler crabs: one of the most speciose, charismatic, and behaviorally complex of all crabs.

Research partly funded by NSERC CGS-D Scholarship (Canada) (to JL), the PCP-PIRE NSF project 0966884 (OISE, EAR, DRL) (to JL and AJWH), the Jon A. and Beverly L. Thompson Endowment (Florida Museum of Natural History) (to AJWH), and the McGinty Endowment at the FLMNH (to RWP).