Revision of the extinct shark Synechodus prorogatus Kriwet, 2003 (Chondrichthyes, Elasmobranchii) and its galeomorph affiliation

The majority of the fossil records of elasmobranch fishes (sharks, rays, skates) consists of isolated teeth and dermal denticles. Over their long and complex evolutionary history, dental remains are particularly indicative of the group’s plasticity and adaptability, which has hampered the classification of fossil species with highly specialised dental morphologies that deviate from those of extant species. One of such cases is †Synechodus prorogatus recovered from Middle and Late Jurassic deposits in Poland and Germany. Its original description and diagnosis were based on a single complete and two very incomplete teeth, which showed a very peculiar morphology with some features resembling several groups. These similarities resulted in its placement within synechodontiforms. However, subsequent findings showing numerous differences with the type species of the genus, †Synechodus dubrisiensis, cast doubt on its assignment within this group and this genus. Here, we describe new material from Upper Jurassic offshore deposits in SW Germany, which provides additional information about this species. We conducted a comprehensive morphological comparison between †S. prorogatus, various Jurassic selachian taxa and the type species of †Synechodus, †S. dubrisiensis (Late Cretaceous, England), confirming the taxonomic distinctiveness of this Jurassic species, which requires the establishment of a new genus, †Curvorudentis, with †C. prorogatus gen. et comb. nov. being type species. The discovery of this taxon in Late Jurassic deposits of Germany represents its stratigraphically youngest occurrence, extending its chronostratigraphic range and geographical distribution. †Curvorudentis prorogatus is considered here a galeomorph shark, rather than being a member of the stem clade †Synechodontiformes, although its precise systematic position within this group remains ambiguous.