Ecology of the "Living Fossil" Holopus rangii (Echinodermata: Crinoidea)

Grant Winners

Dean

Abstract

This project will investigate the ecology and biology of the "living fossil", Holopus rangii, one of only eight living species of Cyrtocrinida, an aberrant, enigmatic group that first diversified during the Jurassic and became perhaps the most diverse crinoid group during the remaining Mesozoic. Crinoids are related to sea stars and urchins. Cyrtocrinids are rarely preserved intact as fossils and their origins remain speculative. H. rangii occurs in several hundred meters depth on steep Caribbean slopes, but significant populations have recently become accessible via submersible off Roatan Island, Honduras. These assemblages include both adult and juvenile living individuals as well as "stumps" of dead specimens; the combination will permit us to examine population structure, feeding, growth, mortality, local distribution relative to substrate and current flow, and recovery from predation. The results will permit us to develop an actualistic model of its poorly known fossil forebears, compare it with other living and fossil cyrtocrinids, and strengthen hypotheses about the early diversification of Mesozoic crinoids, a major contributing group to the fossil record. Data collected will include video, quantitative digital still images, specimens, gut contents, and sediment samples. Image analyses will include size frequency, density, distribution, arm regeneration, and comparisons between living and dead individuals. Comparison of living and dead individuals among sites using statistical inference may offer insights about factors controlling populations, including depth, exposure to bottom currents and protection from sedimentation. Results will be compared with the little data known for other species to develop a broader picture of cyrtocrinid biology that can be applied to their fossil record. Two trips, 9 months apart, will permit measurements of growth and mortality. Collaborators will carry out components focusing on molecular evolution and comparison of living and fossil species. An NSU student will carry out quantitative photo analyses.