SURVIVAL OF THE MORPHOLOGICALLY SPECIAL OR ORDINARY? THE STORY AS TOLD BY FOSSIL CRINOIDS

Temporally long-ranging taxa are thought to have unusual properties that aid their prolonged geologic survival. Dispersal capabilities, geographic ranges and single character morphological adaptations have been studied as factors that may contribute to geologic longevity. In this talk, I present an analysis of crinoid morphology versus longevity, using a large crinoid database, consisting of first and last appearances and morphological characters coded with discrete states for the genera (Foote 1999).

I show that long-lived crinoid genera and families are often less distant from mean morphologies of their crinoid orders than their shorter-lived relatives. Long-lived crinoid genera are morphologically less specialized than expected, when compared with resampled data. I also observe that long-lived crinoid genera are less distant from mean morphologies of their temporal cohorts compared with shorter-lived genera, but not in a statistically significant manner. It will be instructive to know if long-lived taxa are consistently divergent from the most primitive member(s) of a taxonomic group. However, putative basal members used for my analyses gave differing and sometimes contradictory results.

I conclude that long-lived crinoids are relatively unspecialized, in the sense that they are relatively closer to the mean morphologies of their taxonomic groups. This robust result is not due to the lack of morphological characters in very long-ranging genera nor due to their having (sometimes) greater species representations in the database.