A NEWLY HATCHED COILED NAUTILOID FROM THE PERMIAN OF ITALY

Abstract

Well-preserved, newly hatched coiled nautiloids from the late Paleozoic are relatively unusual. Thus, the recovery of a hatchling specimen from the Sosio Limestone (Permian, probably Wordian) of Italy that can be assigned to Sholakoceras cf. S. pleuronautiloides (Gemmellaro, 1890) is notable. The embryonic and posthatchling shell of S. cf. S. pleuronautiloides shows some morphological similarities to Recent Nautilus Linnaeus, 1758; however, some dissimilarities are significant, and these features have implications on the overall phylogenetic pattern exhibited by these organisms through time and the evolutionary processes that led to that pattern. The specimen comes from the extremely fossiliferous Pietra di Salomone megablock southwest of Palazzo Adriano, Sosio Valley (Monti Sicani, western Sicily). This and a couple of similar occurrences (blocks) are informally known as the “Sosio Limestone.” The geographic situation and geological setting were given in detail by Flugel et al. (1991), who also discussed the facies and age of the Pietra di Salomone megablock. These authors recognized carbonate breccias and calcarenites deposited by debris flows and turbidity currents in a base-of-slope position. The calcareous material was originally deposited on carbonate platform margins prior to gravity-induced transport. According to Flugel et al. (1991), most of the Pietra di Salomone megablock has a Wordian (Murghabian) age. However, for some of the pebbles derived from reef facies, a Capitanian (Midian) or even Wuchiapingian (Dzhulfian) age is also possible. Jenny-Deshusses et al. (2000) gave a Capitanian to Wuchiapingian and probably even a Changhsingian age for the Pietra di Salomone megablock. Therefore, the studied nautiloid specimen has a Wordian to latest Permian age. The Sosio Limestone is famous for its well-preserved invertebrate fauna. Overall, more than 300 species of invertebrates have been described from the Pietra di Salomone, and more than 520 species have been reported from all Sosio blocks (Mascle, …