Meeting Abstract
S5.5 Tuesday, Jan. 5 Evolutionary morphology of regenerative abilities among crinoids: a paleontological perspective GAHN, Forest J*; BAUMILLER, Tomasz K; Brigham Young Univeristy-Idaho; University of Michigan gahnf@byui.edu
The fossil record demonstrates that crinoids have had the capacity to regenerate lost body parts since the Ordovician. This ability has been recognized in all parts of the crinoid skeleton. Most regeneration is indicated by an abrupt change in the size of adjacent ossicles. Completed regeneration is difficult to recognize, but the carbon and oxygen isotopic composition of ossicles may be used to distinguish fully healed skeletal elements. Although crinoids have possessed regeneration abilities since their origin, the distribution of regeneration sites within and among crinoid clades has changed through time. Examples of this are specialized autotomy articulations in the arms (syzygies) and stalk (synostoses) for minimizing loss and maximizing recovery potential. Most Paleozoic crinoids lacked such articulations as evidenced by fixed stalks and random patterns of longitudinal arm regeneration. However, syzygies and muscular arm articulations are found among the cladids by the Mississippian, and the most diverse post-Paleozoic crinoids (articulates) shared these traits. The presence of these characters in extant crinoids facilitates mobility and predator avoidance. The frequency of regenerated crinoid arms has also changed through time. Spatiotemporal changes in regeneration frequency are best explained by differences in sublethal predation. Notable patterns include a significant increase in regeneration frequency during the Middle Devonian, a time of dramatic evolutionary radiation among durophagous predators. Moreover, at the community-level, the most abundant species have the highest regeneration frequencies. According to apparency theory and escalation, taxa with higher rates of sublethal predation should also exhibit greater predator-avoidance potential, a testable prediction with both paleontological and neontological data.
