AN UNIQUE UPPER TRIASSIC COLEOID FROM THE AUSTRIAN ALPS REVEALS PRO-OSTRACUM AND MANDIBULE ULTRASTRUCTURE

Abstract

A recently discovered Late Triassic (Lower Camian) coleoid (Doguzhaeva & al., 2005a) from the Austrian Alps (locality Schindelberg, Lunz, Niederösterreich) is described as Lunzoteuthis schindelbergensis n. gen. et sp. The remnants of the small-sized coleoid comprise (1) a fragmentarily preserved, breviconic phragmocone compressed by compaction (about 10 mm broad and 5 mm long; estimated apical angle ca. 15-20°), (2) a proostracum that is discernible by the growth lines on the dorsal side of the phragmocone, and (3) a lower mandible that is relatively large, broad (about 4 mm long), black and glassy. The rostrum is absent. The proostracum in L. schindelbergensis is similar to that in Early Jurassic Beleninotheutis but differs by its narrow central field, bordered by hyperbolar zones, from the tripartite proostracum of the contemporaneous Phragmoteuthis, Middle Triassic Breviconoteuthis and Upper Permian Pertnoteuthis. Contrary to Belemnotheutis, it has no rostrum. The lower mandible in L. schindelbergensis is similar to that in recent squids and bears no resemblance to the structure described as mandibles in Phragntoteuthis (Mojsisovics, 1882). SEM examination shows that the proostracum material in L. schindelbergensis is finely laminated, making it similar to (1) the chitinous gladii in modem squids Loligo and Berryteuthis here studied, (2) the fossil gladii of several squid-like coleoids (Doguzhaeva & Mutvei, 2003; 2005, 2006 herein) and (3) the proostracum of Belemnotheutis (Doguzhaeva et al., 2005b; 2006b herein). The proostracurn in L. schindelbergensis has neither prismatic nor nacreous layers and therefore is not considered to be a projection of the phragmocone wall (conotheca). It is built up of two layers: (1) the inner layer of vertical columnar units formed by micro-lamellae ("organic lamello-columnar" ultrastructure), (2) the outer layer of micro-plates that have a wedge-like shape and are arranged more or less parallel to the surface. The new data supports the concept that the proostracum is an innovative morphological element in coleoid evolution (Doguzhaeva, 2002; Doguzhaeva et al., 2002a, b, 2003a, b, 2005a, b; 2006b herein). The presumable lower mandible of L. schindelbergensis is characterized by broad wings and a distinct beak (= rostrum) that has a thickened anterior edge. The wings are formed by inner and outer laminae fused near the rostrum. The length ratio of the two laminae is unclear because the posterior portion of the mandible was destroyed during preparation. The mandible has a micro-laminated ultrastructure similar to that of chitinous mandibles in Loligo and in the contemporaneous ceratitid Austrotrachyceras from the same locality (Doguzhaeva et al., 2007a in press). In: L. schindelbergensis the mandible must therefore have been originally chitinous. The initial shell ontogeny in Lunzoteuthis n. gen. remains unknown, and the systematic position of the new genus is uncertain. In the gross morphology of the phragmocone and proostracum it is comparable with Belemnotheutis but is distinguished by having no rostrum. It is temporarily referred to the Suborder Belemnoteuthididina Stolley.