Early Jurassic Bivalvia of Argenti¬na. Part I: Stratigraphical Introduction and Superfamilies Nuculanacea, Arcacea, Mytilacea and Pinnacea

DAMBORENEA, S.E.

PALAEONTOGRAPHICA

E SCHWEIZERBARTSCHE VERLAGS

Lugar: Stuttgart; Año: 1987 vol. 99 p. 23 - 111

0375-0442

A detailed systematic study has been made of 23 species of early Jurassic bivalves belonging to 15 genera and subgenera and to six families of the superfamilies Nuculanacea, Arcacea, Mytilacea and Pinnacea. Of these, four species are new: Paralle!odon groeberi n. sp., Parallefodon riccardii n. sp., Lyccttia hypertrigona n. sp. and Modiolus (Gibbomodiola ?) gerthi n. sp. The research was mainly based upon the author's· own material collected stratigraphically. Twenty-three sections were measured and the summarized description of each of them is given. A total of about 50 fossiliferous localities were visited in the provinces of San Juan, Mendoza and Neuquen of western Argentina. Thus, the knowledge about the stratigraphical range of  the species has been greatly improved. Some of the genus-group taxa are recognized and illustrated for the first time in the early Jurassic of Argentina. Severa1 species are identica1 or very closely related to European forms and the bivalves studied show, as a whole, strong affinities with typically Tethyan ones at the generic level. Nevertheless, many of the species have a restricted geographical distribution within the South American Andes. The status of Ashcro.ftia CRICKMAY has been validated as a subgenus of Cucullaea LAMARCK and a species of Modiolus LAMARCK is tentatively referred to the subgenus Gibbolmodiola. SACCO. Furthermore, relevant data for a better understanding of the ontogenetic development of several of the described species and an outline of the palaeoautecology of each species are also given. Palaeogeographical data analysis of genera such as Lycettia Cox and Intopema CONRAD strengthens the available evidence favouring a faunal exchange between the east-central Pacific and the western Tethys during early Jurassic times. to 15 genera and subgenera and to six families of the superfamilies Nuculanacea, Arcacea, Mytilacea and Pinnacea. Of these, four species are new: Paralle!odon groeberi n. sp., Parallefodon riccardii n. sp., Lyccttia hypertrigona n. sp. and Modiolus (Gibbomodiola ?) gerthi n. sp. The research was mainly based upon the author's· own material collected stratigraphically. Twenty-three sections were measured and the summarized description of each of them is given. A total of about 50 fossiliferous localities were visited in the provinces of San Juan, Mendoza and Neuquen of western Argentina. Thus, the knowledge about the stratigraphical range of  the species has been greatly improved. Some of the genus-group taxa are recognized and illustrated for the first time in the early Jurassic of Argentina. Severa1 species are identica1 or very closely related to European forms and the bivalves studied show, as a whole, strong affinities with typically Tethyan ones at the generic level. Nevertheless, many of the species have a restricted geographical distribution within the South American Andes. The status of Ashcro.ftia CRICKMAY has been validated as a subgenus of Cucullaea LAMARCK and a species of Modiolus LAMARCK is tentatively referred to the subgenus Gibbolmodiola. SACCO. Furthermore, relevant data for a better understanding of the ontogenetic development of several of the described species and an outline of the palaeoautecology of each species are also given. Palaeogeographical data analysis of genera such as Lycettia Cox and Intopema CONRAD strengthens the available evidence favouring a faunal exchange between the east-central Pacific and the western Tethys during early Jurassic times.