Ridescrizione di “Rhinobatos” dezigni, un pesce chitarra del Konservat Lagerstätte eocenico di Bolca = Redescription of "Rhinobatos" dezigni, an Eocene guitarfish from the Bolca Konservat-Lagerstätte

The order Rhinopristiformes is a well-diversified group within the Batoidea that includes guitarfishes and sawfishes with about 60 species arranged in 12 genera. Guitarfishes are world-wide distributed and are found in continental and insular shelves from coastal to abyssal depths in warm to temperate waters. The representatives of this group probably appeared in the Toarcian (Early Jurassic) and their fossil record is mainly represented by isolated teeth and rare complete and articulated specimens coming from Mesozoic deposits. The only complete and articulated specimens of Cenozoic guitarfishes known so far are represented by “Rhinobatus” dezigni and “R.” primaevus, from the upper Ypresian Bolca Konservat-Lagerstätte. Here I present a detailed analysis of the holotype of “Rhinobatos” dezigni (Heckel, 1853), originally referred to the genus Trygonorhina and later assigned to Rhinobatos by Jaekel (1894). The specimen, presently housed at the Museum of Natural History of Vienna (NHMW 1853.XXVII.4), was originally donated by baron Achille De Zigno (1813-1892) to the Royal Court of Vienna in 1853, following the failed attack in which the Emperor Franz Joseph I was involved. The study of the fossil, preserved as part and counterpart, includes direct observations of the anatomical parts, including those observable using the UV technique. “Rhinobatos” dezigni preserves elements useful for its identification, including the chondrocranium, parts of the jaws, elements of hyoid and gill arches, part of the pectoral and pelvic girldles, as well as the synarcual and vertebral column. Most of the characters observed in “Rhinobatus” dezigni confirm its attribution to the order Rhinopristiformes. Moreover, the phylogenetic analysis of the taxon, based on 95 characters, suggests that it is deeply nested within the family Trygonorrhinidae. Its unique anatomy, however, including a rhinobatid-like tooth morphology, differentiates the Heckel's species from all the representatives of the family (Aptychotrema, Trygonorrhina and Zapteryx). As a consequence, I propose herein to create a new genus for the rhinobatoid from Bolca, provisionally named Pseudorhinobatos.