Preliminary study of an astropectinid (Asteroidea; Echinodermata) from the Lower Cretaceous (Mulichinco Formation) of the Neuquén Basin, Argentina

FERNÁNDEZ, DIANA E.; PÉREZ, DAMIÁN E.; LUCI, LETICIA

La Plata

Congreso; Xº Congreso Argentino de Paleontología y Bioestratigrafía y VII Congreso Latinoamericano de Paleontología; 2010

Universidad Nacional de La Plata

Body fossils of any group of starfish are rarely preserved; mostly they comprisedissociated ossicles only. Astropectinids in particular have a limited fossil record,although they are environmentally broad ranging and numerically important in recentsettings. The Mulichinco Formation (Early Valanginian, Mendoza Group) is a clastic,mainly marine and marginal-marine succession, exposed in the Neuquén province. Thesample was recovered from the lowermost levels of this Formation, in the outcropslocated along the National Road 40 at the Pampa Tril area (37º 15? S, 69º 47? W). Thesandstone containing the specimen represents the top of one of several coarseningupward successions interpreted as shoreface deposits. The sample is a very wellpreservedstarfish in oral view. The central area (disk) and the five rays can be identified(two of them are complete, one is almost complete, and two are fractured showing lessthan a third of their original length). The ambulacral grooves, the inframarginal platesand some of the adambulacral plates corresponding to each of the rays are alsoobservable. The members of the Astropectinidae family exhibit a rather small disc, longand normally straight-sided arms, and contact facets between marginals smaller than thesides of these ossicles. All of these features can be observed in this sample. The firstrecords of the Astropectinidae come from Jurassic deposits. The only Mesozoic recordsof this family come from Europe and North America. This specimen represents,therefore, the first known evidence of the existence of this group of starfish in theCretaceous of South America.