Re-evaluation of German Stenopterygius in Italian museums: updated identification and morphofunctional inferences

Fossil remains of the genus Stenopterygius (Ichthyopterygia, Parvipelvia) are mostly found in Lower Jurassic strata of the Württemberg area, Germany. Several complete and articulated specimens of Stenopterygius have been recovered from the famous locality of Holzmaden (Württemberg) and sold to museums throughout Europe since the early 19th century. Many Stenopterygius skeletons arrived to Italian palaeontological collections, however, most of them have never been properly studied. Because of their presence in many museums worldwide, Stenopterygius fossils represent an ideal statistical sample for investigating the inter- and intraspecific morphological variability of this genus. Here, we report on 19 ichthyosaur skeletons from five Italian museums (Museo Geologico Giovanni Capellini, Museo Geologico Paleontologico dell’Università di Padova, Museo di Paleontologia di Napoli, Museo di Storia Naturale di Milano, Museo di Storia Naturale dell’Università di Pisa) identified as Stenopterygius using modern taxonomic schemes. Updated species-level identifications of these fossils were attempted by relying on the linear morphometric analyses previously proposed by other authors. Out of 19 studied specimens, eight were assigned to Stenopterygius quadriscissus, three to S. triscissus, with all other specimens being referred to Stenopterygius cf. quadriscissus, Stenopterygius cf. triscissus or Stenopterygius sp. Including these 19 specimens in morphometric analyses improved the precision of these methodologies by increasing the statistical sample size. The studied specimens were documented by high-resolution photographs and 3D models. Two skeletons kept at the Museo di Storia Naturale dell’Università di Pisa (MSNUP) were CT-scanned, revealing interesting anatomical elements, such as the hyoid bones and ischiopubis, which would have been otherwise hidden beneath the embedding limestone. CT-scans resulted in the reconstruction of the tridimensional rostral morphology of one of the MSNUP specimens, allowing some morphofunctional inferences on the feeding behavior of Stenopterygius. The rostra of some long-snouted odontocetes and istiophoriforms may represent good functional analogues of those of parvipelvian ichthyosaurs.