Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 88. (Budapest 1996)

Dulai, A.: Taxonomic composition and palaeoecological features of the Early Badenian (Middle Miocene) bivalve fauna of Szob (Börzsöny Mts, Hungary)

TAXONOMIC COMPOSITION OF THE FAUNA At the museum collection (Fig. 2a) gastropods are the most frequent (74%), bivalves are important (23%) and the other groups are in insignificant minority. At the washed material (Fig. 2b) bivalves are the most frequent (46%), gastropods are significant (26%), but more than one-quarter of the fossils are composed of the other groups (worm tubes, bryozoans, vertebrates, decapods, scaphopods). The specimen number is nearly three times larger at the washed material, than at the museum collection, but at the same time the species number is more than twice as much at the museum collection. The difference in abundance continuously decreases between the two collections at higher taxonomic levels (genus, family and superfamily) and the washed material is more diverse at the level of orders due to the small fragment of Clavagella (Stirpulina) in the washed material (Table 1) (DULAI in prep.). The most frequent bivalves are generally nearly equal in the two collections or slightly more abundant at the museum collection, except the two most frequent species Corbula gibba and Corbula carinata - at which the percentage of these species is much larger at the washed material (Fig. 3). The amount of these two species is about 84% in the washed fauna, while only 53% in the museum collection. At the other species there are no such significant differences. The taxonomic structure of the fauna is given in Table 2. The bivalve fauna is very diverse at higher taxonomic levels but at the same time very poor at lower taxonomic levels. 18 families contain only one genus each in the museum collection. Four families Table 1. Taxonomic composition of the two collections (1: collection of the museum; 2: washed material) 1 2 1628 specimens 4478 specimens 66 species 29 species 45 genera 25 genera 26 families 18 families 20 superfamilies 16 superfamilies 5 orders 6 orders Fig. 2. Taxonomic composition of the studied Szob material: a = collection of the museum, b = washed material