HYBRID CRINOIDS IN THE FOSSIL RECORD (EARLY MISSISSIPPIAN, PHYLUM ECHINODERMATA)

Potential hybrid fossil crinoids, Eretmocrinus magnificus x Eretmocrin us praegravis, are identified from the Lower Mississippian Fort Payne Formation of south-central Kentucky. These are the first fossil hybrid crinoids identified, and one of very few examples of hybrids recogniz ed in the fossil record. Eretmocrinus magnificus x E. praegravis speci mens have shapes and calyx plate sculpturing that are morphologically intermediate between well-defined, distinct parent species. Suspected hybrids occur at localities where parent species co-occur and where th e parent species are the most abundant; the hybrids occur at what may have been the distributional margins of the parent species; and the mi xture of characters on suspected hybrids seems to be morphogenetically partitioned. Parent species are derived from separate lineages within Eretmocrinus, and hybridization is the most probable explanation for these morphologically intermediate specimens. This example highlights the need to consider hybridization as a potential interpretation of in termediate morphologies among fossils and raises questions concerning the impact of hybridization for our interpretation of the fossil recor d and the role of hybridization in the evolutionary process.