A test of Simpson's "rule of the survival of the relatively unspecialized" using fossil crinoids.
Temporally long-ranging (=long-lived) taxa have been postulated to have unusual properties that aid their prolonged geologic survival. Past studies have examined dispersal capabilities, geographic ranges, and single-character morphological adaptations as factors that may contribute to geologic longevity. Here, I test whether long-lived fossil crinoid taxa are morphologically unusual using a whole suite of morphological characters. I define long-lived taxa in several explicit, comparative ways. I find that long-lived crinoid genera and families are often less distant from mean morphologies of their crinoid orders than their shorter-lived relatives; that is, they are relatively less specialized. I also compare the morphology of crinoid genera relative to basal members of their respective orders; mean morphological distances of long-lived genera from basal morphologies are seldom distinct from those of their shorter-lived relatives. I 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. I conclude that long-lived crinoids are relatively unspecialized, in the sense that they are relatively closer to mean morphologies of their taxonomic groups.
Liow
Lee Hsiang
LH
Committee on Evolutionary Biology, University of Chicago, Chicago, Illinois 60637, USA. lhliow@midway.uchicago.edu
D000818:Animals; D004447:Echinodermata / Q000033:anatomy & histology / Q000145:classification / Q000502:physiology*; D053476:Extinction, Biological; D005580:Fossils; D008954:Models, Biological; D010802:Phylogeny