FIRST SKELETAL REMAINS OF <em>HELVETICOSAURUS</em> FROM THE MIDDLE TRIASSIC ITALIAN OUTCROPS OF THE SOUTHERN ALPS, WITH REMARKS ON AN ISOLATED TOOTH

Abstract

The enigmatic marine reptile Helveticosaurus zollingeri, from the Middle Triassic Besano Formation of Monte San Giorgio, is known from three specimens found in Swiss territory. This paper describes the first skeletal remains of this taxon recovered from the corresponding Italian outcrops of Besano (Varese). An isolated tooth assigned to the same taxon and coming from the San Salvatore Dolomite, Rasa di Varese (Varese), is also redescribed herein. The skeletal remains have been CT scanned to inspect the preserved morphology of the bones hidden below the surface; CT data also allowed the identification of an associated ammonoid which has been crucial to determine the stratigraphic position of the studied material. The redescription of the tooth has been helped by a digital model of the specimen obtained through photogrammetry. With the additional new data obtained from the two specimens, the first skeletal reconstruction of Helveticosaurus is provided. This is followed by a phylogenetic test of the taxon, assessing its position among marine Triassic diapsids. Finally, in the light of recent studies we discuss the swimming mode and the possible ecological niche occupied by the animal: we suggest a distinction between the function of forelimbs and hindlimbs, and a distinction between different swimming styles likely performed by Helveticosaurus, depending on the speed of movements.

Ontogenetic variation in the cranium of Mixosaurus cornalianus, with implications for the evolution of ichthyosaurian cranial development

“…The Besano Formation was deposited in a shallow marine setting (30–130 m deep) and consists of an alternation of laminated dolomitic banks and bituminous shales, with sparse cineritic tuffs (Bernasconi & Riva, 1993 ; Furrer, 1995 ; Röhl et al, 2001 ), which are Late Anisian–Early Ladinian in age (Brack & Rieber, 1993 ; Brack et al, 2005 ; Mundil et al, 1996 ; Wotzlaw et al, 2017 ). The material studied originates from the middle part of the Besano Formation, which is dated to the latest Anisian, was deposited in an intraplatform basin (Röhl et al, 2001 ), and from which a great number of ichthyosaurian remains and other pelagic vertebrates were recovered [e.g., Furrer, 2003 ; Bindellini et al, 2021 ; Brinkmann, 1997 ; Renesto et al, 2020 ; Dal Sasso & Pinna, 1996 ; Bindellini & Dal Sasso, 2022 ]. Specimens in the Besano Formation are almost ubiquitously preserved laterally or dorsoventrally flattened, however in most cases some original 3d relief is preserved even in fetal material (Miedema et al, 2020 ; Spiekman et al, 2020 ).…”