Abstract

CARRERA, Marcelo G.  and  ERNST, Andrej. Darriwilian bryozoans from the San Juan Formation (Ordovician), Argentine Precordillera. Ameghiniana [online]. 2010, vol.47, n.3, pp.343-354. ISSN 1851-8044.

A detailed study is carried out on the taxonomy of the bryozoan fauna from the upper levels of the San Juan Formation (Darriwilian) in the Talacasto and Cerro Viejo sections, Argentinean Precordillera. Three bryozoan genera are described and two new species are erected: Lamottopora multispinosa sp. nov., Aostipora sanjuanensis sp. nov., and Phylloporinidae sp. indet. The paleoecological significance of the bryozoan fauna is discussed. The ramose bryozoans Lamottopora and Aostipora dominate in the Talacasto section. Some colonies probably lived attached directly to the substrate, while others occur attached to the surface of the abundant sponge fauna in the section. The majority of bryozoans at the Cerro Viejo section occur as epibionts, with bases attached to the surface of sponges. Bryozoans collected in the matrix are scarce compared to the Talacasto section, and comprise a few fragments of ramose bryozoans and two small fragments of the reticulate Phylloporinidae sp. indet were recorded exclusively in this locality. The presence of this delicate form in Cerro Viejo is further evidence of the quiet water conditions suggested for these levels. Only the laminar form Nicholsonella occurs in slightly older levels (Floian) of the San Juan Formation. The low diversity recorded here shows a slight decoupling with the global pattern. The first local radiation (three genera) is minor compared with the important radiation that the phylum experienced elsewhere.

Keywords : Bryozoans; Ordovician; Argentina; Precordillera.