Eocene asteroids (Echinodermata) from Seymour Island, Antarctic Peninsula

This chapter augments the work of Blake and Zinsmeister (1979) on asteroids of the upper Eocene La Meseta Formation, Seymour Island, Antarctic Peninsula. Buterminster elegans n. gen. n. sp. (Goniasteridae) is described, and small Zoroaster aff. Z. fidgens (Zoroasteridae), a four-armed Ctenophoraster downeyea (Astropectinidae), and an undetermined species of Sclerasterias(1) (Asteriidae) are reported and evaluated. Asteroids are rare in most fossil faunas but common in the La Meseta Formation; the poor record of asteroids is attributed to body construction and habits rather than to a geologically recent diversification. Asteroids, especially members of the Asteriidae, are important in determining structure of many modern communities. The presence of an asteriid species in the La Meseta Formation fauna suggests a community structure parallel to certain modern examples. Elsewhere, the La Meseta Formation has been inferred to have been deposited in moderately high-energy, shallow water; in contrast, modern Sclerasterias (in Antarctica), Zoroaster, and Ctenophoraster are known only from relatively deeper waters. Three small Zoroaster aff. Z. fulgens are preserved with their arms extended above the disc, apparently buried while suspension-feeding. This posture is rare among asteroids and has not been reported among modern members of the Zoroasteridae. Morphologic differences between La Meseta Formation asteroids and their closest modern biologic allies are relatively minor, suggesting slow evolution. Modern species closely related to the fossil species are known from southern oceans; no major biogeographic changes are evident.