A brittle star bed from the Miocene of Patagonia, Argentina

MARTINEZ SERGIO,; DEL RIO, CLAUDIA JULIA; PEREZ DAMIAN

LETHAIA

WILEY-BLACKWELL PUBLISHING, INC

Lugar: COPENHAGEN -LONDRES; Año: 2010 vol. 43 p. 1 - 9

0024-1164

is important. The Miocene example studied herein involves the recently describedspecies Ophiocrossota kollenbergorum Caviglia, Martínez & del Río recovered from theChenque Formation of southeastern Argentina. The information used here is derivedfrom unpublished data and a new record from two discrete, thin, monospecific patches.The main taphonomic features of the patches, namely the presence of specimensconcordant with bedding planes, (with either aboral or oral side upwards), and the goodpreservation of the delicate discs (ca. 6 mm wide on average), and the preservation ofun-oriented arms complete with fragile tips (not wider than 0.2 mm), point to a suddenlyburied census assemblage. Although broken or isolated arms were found, this is attributedto the erosive environmental conditions of the abrasion platform where the studiedexposure is located today. Size frequency distributions suggest that both patches wereburied at different seasons. Observed densities are 77 and 143 individuals/m2 and distancesbetween individuals are random. The arm length/disc diameter ratio indicates thatOphiocrossota kollenbergorum may have been an epifaunal surface dweller. No signs ofpredation (such as regenerated arms), were identified.