Asteroid (Echinodermata) skeletal elements from upper Oligocene deposits of Jamaica and Antigua

Abstract

The Antillean Cenozoic fossil record of asteroids comprises mainly dissociated ossicles. Most common among isolates from upper Oligocene deposits of Jamaica and Antigua are marginal ossicles of an extinct, indeterminate species of Pycinaster. This is the youngest known occurrence of the genus and the first from beyond Europe. A number of relatively complete fossils have been assigned to Pycinaster and (sub)familial status proposed for it together with Phocidaster. The latter proposition is based solely on a few marginals, but available diagnoses are judged insufficient to justify such recognition. The taxon Pycinasteridae is here synonymized with the Goniasteridae, although future study of added features (such as the ventral surface) might justify recognition at a higher taxonomic level. In addition to ossicles assigned to Pycinaster, many marginals are tentatively assigned to the surviving goniasterid Nymphaster. Numerous generic and many species names have been based on asteroid isolates, but the practice demands assumptions that are not readily justified. Linkage of discrete isolates under a single taxon name assumes derivation from a single source, an inference that can be verified only rarely (if ever), therefore reducing names to the single holotype ossicle. Availability of only isolates encourages comparison with extant taxa and biogeography, biasing interpretations with a Holocene overlay. Because of these constraints, a new nominal species of Pycinaster is not justified and assignment of ossicles to Nymphaster is tentative. However, given the importance of asteroids in marine communities, we emphasize the significance, largely ignored, of their presence in Cenozoic deposits of the wider Caribbean.

Two new early Asteroidea (Echinodermata) and early asteroid evolution

“…Actinal shapes and arrangements among interbrachia in Aerliceaster n. gen. are all but chaotic (Fig. 1), whereas actinal configurations among extant asteroids are regular, regularity having been argued as emerging independently among clades (Blake and Hotchkiss, 2004, p. 361; Blake et al, 2015a, p. 1049). Data for Kolataster n. gen. are not available.…”

An asteroid (Echinodermata) faunule from the Oxfordian Swift Formation (Upper Jurassic) of Montana

“…Many families, however, include few taxa, and familial morphologic ranges and abundances surely have changed through geologic time. Assigning ancient specimens to an inferred most-similar extant taxon imposes contemporary concepts on potentially significant evolutionary change (Blake and Reboul, 2011; Blake et al, 2015), thereby misleading interpretation of taxon history.…”

A new species of the asteroid genus Betelgeusia (Echinodermata) from methane seep settings, Late Cretaceous of South Dakota

“…Actinal ossicular alignment immediately adjacent to the mouth frame of B. brezinai appears to have been somewhat irregular, reminiscent of corresponding expressions in both Triassic Trichasteropsis Eck, 1879 (Blake and Hagdorn, 2003) and a species of Pycinaster Spencer, 1907 (Blake et al, 2015). Abundant actinals, uncommon among Paleozoic asteroids, might have arisen as a space-filling device for disk enlargement, the ossicles only later and homoplastically becoming more strongly aligned, perhaps to form efficient water channels or to enhance body flexibility (Blake and Hotchkiss, 2004).…”