J. Wyatt Durham

EVOLUTION AMONG THE ECHINOIDEA

Our understanding of the evolution of any group of organisms is based upon data from the fossil record and our knowledge of extant representatives. T h e echinoid skeleton is an endoskeleton, of mesodermal origin, and thus differs markedly from that of all other metazoa except the chordates. It is likewise very complexly organized, composed of a multiplicity of parts, many of them specialized for particular functions. There are probably few, if any, adult echinoids that have less than 1000 piecesincluding spines, spicules, plates, pedicellaria and lantern, as well as the test-in their skeleton. Many echinoids with numerous small spines probably have over

Movement of the Caribbean plate and its importance for biogeography in the Caribbean

Sykes et al. have demonstrated that the Caribbean plate has moved east-northeast about 1400 km since late Eocene time (38 Ma). This movement changes or affects the interpretation of many biogeographic problems of that region. For example, Woodring9s 1965 “Middle Miocene Caribbean Province,” although slightly larger peripherally, includes the same area as the Caribbean plate; the migration route by which the North American terrestrial mammals reached the Panamanian area in the early Miocene may have been via the Nicaraguan Rise rather than through present-day Guatemala; Petuch9s “relict Neogene gastropod fauna” from northern Colombia and Venezuela may have been carried along with the plate as it moved; the otherwise Pacific keyhole echinoid genus Mellitella9s anomalous fossil occurrences in Venezuela and Colombia are explained by the plate movement.