Taxonomy of Rudists from the Campanian Transgressive Sediments of Brašljevica, Donje Orešje and Sv. Martin, Northern Croatia

Abstract

Rudists are common fossils in transgressive Upper Cretaceous deposits in three localities placed in northwestern part of Croatia. Their appearances coincide with the beginning of a transgressive sequence through floatstones-thickets. Within the rudist community, Vaccinites Fischer 1887, Hippurites Lamarck 1801 and Hippuritella Douvillé 1908 could be differentiated according to their general or generic morphological elements. The age of deposits was obtained from the Sr-isotope composition of the rudist shells as well as the micro- and nannofossil community from sediments overlying the rudists-bearing sediments at the Donje Oresje and Brasljevica localities. According to this data the age of the transgressive sediments are determined as Early Campanian. Morphological elements (ligamental ridge, pillars, inner diameter, length of the contour around the inner margin of the outer shell layer, and the ratio between this length and the distance between the sutures of the pillars) from the transverse shell sections permit possible definition of different species within the family Hippuritidae, Gray 1848. Transverse shell sections of analyzed Vaccinites, Hippurites and Hippuritella specimens show different values of measured morphological elements as well as their ratios which, subjected to cluster analysis (Ward's and Unweighted pair-group methods), represent grounds for possible taxonomic determination of the species Vaccinites cornuvaccinum (Bronn 1831) at all localities; V. giganteus (d'Hombres-Firmas 1838) and V. vesiculosus (Woodward 1855) at Brasljevica and Donje Oresje; as well as Hippurites vidali Matheron 1880 and Hippuritella lapeirousei (Goldfuss 1840) at Donje Oresje.