REMARKS ON THE ENCHODONTID FISHES FROM THE ATLÂNTIDA FORMATION, PELOTAS BASIN
PABLO M. COELHO, VALÉRIA GALLO AND FRANCISCO J. DE FIGUEIREDO
Departamento de Biologia Animal e Vegetal; Instituto de Biologia Universidade do Estado do Rio de Janeiro.
Presented by DIOGENES DE ALMEIDA CAMPOS
The Pelotas Basin is a passive margin basin type spreading from the coast of Uruguay to the south of Brazil. It has an area of 210,000km2, from which 15% are emerged regions. This basin reaches eastward the isobath of 2,000m. Since 1995, the Brazilian petroleum company PETROBRAS has extracted drill-core samples from this basin, particularly in the Atlântida Formation, at a sediment depth around 4,000m, revealing the occurrence of fishes and mollusks. This stratigraphic unit consists of shales, siltstones, and carbonates, suggesting a neritic paleoenvironment from outer shelf. Calcareous nannofossils and palynomorphs indicate a range from upper Albian to lower Turonian age. Concerning the paleoichthyofauna, we identified an enchodontid as belonging to the genus Enchodus based on the morphological pattern of the skull roof. This genus comprises about 26 species, listed for Cretaceous formations of the Old and New Worlds, mostly described on the basis of mandible and teeth remains. The taxon from the Atlântida Formation is similar to Enchodus venator from the Upper Cretaceous of Morocco in various features ( e.g., shape and position of the nasals; large and knobbly frontals covering most of the skull roof; topographical position of the dermosphenotic; and trajectory of the sensory canals of the skull roof). Nevertheless, this fish can be distinguished from E. venator by the presence of a medioparietal skull, enlarged mesethmoid, triangular dermosphenotic, digitate fronto-parietal suture and pterotic with a sharp posterior border.
Another enchodontid fish of the Pelotas Basin is Rharbichthys ferox also known of the Cenomanian of Africa (Morocco) and Cenomanian-Turonian of Europe (Italy). It is represented by bony elements of the hyobranchial apparatus and mandibles.
Enchodontids, in association with dercetids and primitive holocentroids, occur in faunal assemblages of Cretaceous formations of Africa, Italy, and Brazil indicating probable ancient ecological relations between those demersal predators. These taxa are widely distributed along this large geographic belt and in the case of Rharbichthys is unaffected by sequential vicariant events that determined major geological aspects in the Tethyan Sea. ( December 20, 2001 ).
Publication Dates
-
Publication in this collection
17 July 2002 -
Date of issue
June 2002
