The first record of nautiloids (Cenoceras intermedius) from the early Pliensbachian of Rgotina, (Getic nappe, eastern Serbia)

Abstract

ABSTRACT Cenoceras intermedius (J. Sowerby) is one of the most widespread species among the Early Jurassic nautiloid fauna and its geological range still controversial up to the present day. The specimen of Cenoceras intermedius from the sandy bioclastic limestones of Rgotina (Getic nappe of eastern Serbia), is a large half conch representing the phragmocone. Viewing our findings in light of previous results suggests the main morphological changes occurred during the ontogenetic evolution. The coiling starts with a round-square whorl section, to become almost quadrangular (penultimate whorl) and trapezoidal-triangular for the last one. Moreover, the siphuncle foramen moves within the septum towards the venter border from a slight upper position against the centre in the inner whorls. It exhibits a typical suture line for the genus Cenoceras with two saddles and three lobes. This finding certainly extends the geological range of the species to after the Sinemurian contrary to several earlier works that confined it only to this stage. This assertion is based on the accurate assignment of the nautiloid-bearing bed of Rgotina to the early Pliensbachian by the index species Uptonia jamesoni. The Serbian specimen supports the species’ palaeobiogeographic widespread range within the north-western margin of the Neo-Tethys Ocean framework.