Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 18. 1996. (Budapest, 1996)

FRAGMENTA MINERALOGICA ET PALAEONTOLOGICA 18. BUDAPEST, 1996 p. 19-29 Bivalve ecology in the Pliensbachian (Lower Jurassic) of the Bakony Mts. (Hungary). Description of a new species of Eopecten by I. Szente SZENTÉ, I. (1996): Bivalve ecology in the Pliensbachian (Lower Jurassic) of the Bakony Mts. (Hungary). Description of a new species of Eopecten. - Fragm. Min. et Pal., 18: 19-29. Abstract: In the Bakony Mts. the Pliensbachian stage is represented by deeper-water facies characteristic of the peri-Mediterranean Lower Jurassic. Large-scale collecting work resulted in a moderately diverse bivalve fauna comprising nearly 500 specimens belonging to some 30 taxa. Paleoecological analysis of the bivalve assemblages representing the main depositional environments (tops and slopes of seamounts as well as basins between them) suggests that distribution of bivalves was controlled by the nature of substrate and by the food supply. Suspension feeders are by far the dominant feeding group. Possibly micro-carnivorous bivalves mainly inhabited basinal environments. Seamounts were populated by epifaunal byssally attached genera such as Praechlamys, Parainocerannts, Limea (Pseudolimea) and Plagiostoma. Among pectinids smooth or finely ornamented scallops aie especially characteristic of seamount top environments. Beside the abundant Parainoceramus, deep and shallow burrowing taxa (Pleuromya, indeterminate heterodonts) as well as presumably anomalodesmatan bivalves characterize the assemblage of basinal sediments. INTRODUCTION The Pliensbachian is by far the best studied stage of the Jurassic system in the Bakony Mts. In the sixties and early seventies more than twenty thousand specimens of fossil macro-invertebrates were collected bed-by-bed at several localities by the staff of the Hungarian Geological Institute, lead by the late Dr. J. KONDA. The bulk of the material comprises ammonites, whose studies resulted in a refined biostratigraphy of the sections. Various aspects of the paleobiology of ammonites, brachiopods and gastropods were dealt with by B. GÉCZY, A. VÖRÖS and J. SZABÓ, respectively. The bivalves, as the fourth important fossil group, received less attention in the past. This study investigates the ecology of bivalves with special reference to the ecological composition of the assemblages (bivalve biofacies) representing different sedimentary environments. Some taxonomical remarks as well as description of a new species of Eopecten are also added, and some species, mainly hitherto not documented ones or of other interest, are figured.