HOMEOMORPHY IN THE ASTEROIDEA (ECHINODERMATA); A NEW LATE CRETACEOUS GENUS AND SPECIES FROM COLORADO

Abstract

Codellaster keepersae new genus and species, from the Upper Cretaceous Codell Sandstone Member of the Carlile Shale of Colorado (U.S.A.), is assigned to the asteroid (Echinodermata) family Goniasteridae. Although clearly a goniasterid, the flattened body form and details of morphology of C. keepersae are remarkably similar to corresponding features of the modern astropectinid Astropecten regalis and also of the luidiid Luidia (Platasterias) latiradiata. The discovery facies of C. keepersae includes low-angle crossbeds and asymmetrical ripple marks that are suggestive of a very shallow marine environment. Both the modern species occur in shallow, turbulent settings, and homeomorphy beween ancient and modern asteroids suggests similar selective pressures and evolutionary responses. Limited evidence suggests goniasterids might have been more common in shallower waters during the Cretaceous than they are today, and absence of modern Codellaster-like goniasterids indicates that the family abandoned these habitats, although the fun- damental morphological response to such settings remained viable for asteroid organization.