First report of a Late Paleozoic sponge from Argentina: a Tournaisian (Mississippian) hexactinellid from the Sierra de Las Minitas, La Rioja Province.

RUSTÁN, J. J.; CARRERA, M.; VACCARI, N.E:

General Roca

Congreso; 11º Congreso de la Asociación Paleontológica Argentina; 2016

Asociación Paleontológica Argentina

A hexactinellid sponge has been found in the Agua Quemada area, Sierra de Las Minitas, La Rioja province. It comes from nodules of a thick black fossiliferous mudstone interval underlying a diamictitic glacigenic bed, approximately 100-150m below the record of the Tournaisian guide spore Waltzispora lanzonii Daemon, 1974. Two small, obconical to palmate (3 cm long) specimens have been found. The wall consists of box-like meshes outlined by spicular bundles of hexactins and hexactine-based spicules and small monaxons. The skeletal grid has typical rectangular reticulation of dictyosponges; with primary quadrules nearly 2 mm high and 1.5 mm wide, and spicule tracts of 0.1-0.3 mm wide. A second orderquadrules only observed in well preserved areas are approximately 0.5mm high and 0.5 mm wide. Vertical tracks are coarse (tridimensional) and mainly supported by long rayed hexactins. These characters are included in the diagnoses of the Family Dictyospongiidae. Our taxon is probably related to Clathrospongia Hall, 1882, Thamnodictya Hall 1884 or Thysanodictya Hall and Clarke, 1898, all Included in the Subfamily Thysanodictyinae, which exhibits typical coarse ridge-like, quadrate mesh of spicule bundles based on pentactins and hexactins. This new finding from Argentina improve the extremely poor Late Paleozoic sponge record from South America, otherwise including scarce records in the Permian ofBrazil and Venezuela and a single hemidiscosan hexactinellid from the Carboniferous of Uruguay.