Taxonomic revision of the Lake Pannon cockle subgenus Lymnocardium (Budmania) Brusina, 1897

The lymnocard subgenus Budmania is characterized by the most unusual and spectacular morphology in the endemic mollusc fauna of the late Miocene – Pliocene Lake Pannon. Budmania possessed extremely high, hollow, irregular keels on its ribs, a pattern that was long considered an adaptation to the fluid, muddy substratum. Eight species were described with this pattern between 1874 and 1973. Our revision, based on the type materials and a large number of other specimens from several collections revealed, however, that only two species can be distinguished with certainty: Lymnocardium (Budmania) ferrugineum (Brusina, 1874) and L. (B.) cristagalli (Roth, 1878). The former lived in the littoral zone of Lake Pannon, on sandy substratum, whereas the latter inhabited the sublittoral zone with muddy substratum. This habitat partitioning challenges the interpretation of the high, hollow keels as an adaptation to soft, muddy substratum. The occurrence of both species seems to have been restricted to 7.5-7.15 Ma.