ANEW FOSSIL GONIASTERIDAE (ECHINODERMATA, ASTEROIDEA) FROM THE EOCENE BILL HILL LOCALITY, LA MESETA FORMATION, SEYMOUR/MARAMBIO ISLAND, ANTARCTICA

E. OLIVERO; LÓPEZ CABRERA, M.I.

Punta Arenas

Congreso; IX Congreso Latinoamericano de Ciencia Antartica; 2017

Instituto Antártico Chileno

The Goniasteridae comprises the most diverse family among the Asteroidea with extant species having world-wide distribution and living predominantly in shelfal cold waters, but they are rare today in Antarctica (Mah, 2011). The family is characterized by heavily calcified endoskeletons, robust body outline with tabulate marginals and well-defined actinal and abactinal plates. Its fossil record goes back to the Jurassic, but complete specimens areunusual and most fossils consist predominantly of isolated ossicles, making comparison with extant taxa difficult (Blake and Aronson, 1998). In this regards the Eocene goniasterid record of the La Meseta Formation is unique, including almost complete specimens of Tessellaster clarcki Blake and Aronson 1998, Paragonaster clarcke Blake and Aronson 1998, Pentagonaster (=Buterminaster) elegans (Blake 1988), and probably Cladaster carrioni Medina and Del Valle 1983 (F.A. Medina, personal communication).Here we document another exceptionally well-preserved fossil asteroid from the Eocene Bill Hill locality (Lat. S 64°15´33.1´´; Long. W 56°44´22.7´´) of the La Meseta Formation (Fig. 1). It is probably a new genus and species included in the family Goniasteridae (Figs. 2, 3). The specimen is characterized by prominent marginal plates defining a pentagonal body outline with short arms and weakly concave interradials, well-developed abactinal and actinalplates, distinctive carinal series, and granules on actinals and around abactinals and marginals. The goniasterids Pentagonaster and Tosia, whose extant species are restricted to Australia and New Zealand, show the closest affinities. However, Pentagonaster shows no granules on actinal plates, and the terminal plate of the Eocene Pentagonaster elegans from the La Meseta Formation is distinctly enlarged into toe-shaped single plate. Species of Tosiabear similar pentagonal to weakly stellate body shape, rounded arm tips and marginals symmetrically rounded and convex, but differ in the arrangement of superomarginal and inferomarginal plates and also lack granules on actinals (Mah, 2007). Complete asteroid specimens are rare in the fossil record and special conditions are required in order to preserve the ossicles articulated. At the Bill Hill locality of the La Meseta Formation the new fossil goniasterid is associate to well-preserved brachiopods, bryozoans,echinoids, serpulids, corals, one fully articulated Polyplacophora specimen (Leptochiton sp.)and one specimen of Pentagonaster elegans (Fig. 4). The association represents a living community inhabiting the hard substrate provided by the side walls of an incised valley eroded in Cretaceous sediments (Fig. 5; see López Cabrera and Olivero, 2011). Short transportation and rapid burial during storms events are interpreted to favor the preservation of the delicate fossil assemblage of the Bill Hill locality, including the new fossil goniasterid.