Abstract

Over 80 years the actinopterygian genus Eosemionotus was known from a single species, E. vogeli, from the German Muschelkalk (Anisian). A second species was published in 2004, E. ceresiensis, from the upper Besano Formation (lowermost Ladinian) of Monte San Giorgio, Switzerland. New excellently preserved specimens recovered from the Cassina and Sceltrich beds (Meride Limestone; Ladinian) in this latter area, triggered a new study. Consequently, three new species are established: E. diskosomus, E. sceltrichensis, and E. minutus, including differential diagnoses for the five species, which differ in body proportions, relative position of the fins, the morphology of several skull bones, squamation pattern, and some meristic characters (e.g., number of premaxillary teeth, and branchiostegal rays). The cladistic analysis retrieved Eosemionotus as the oldest Macrosemiidae within the order Semionotiformes (Ginglymodi). The monophyly of the genus and its sister-group relationships with the other macrosemiids are among the best supported nodes with high Bremer, jackknife and bootstrap values, and numerous synapomorphies. The pattern of phylogenetic relationships between the five species of Eosemionotus indicates that the Muschelkalk species E. vogeli originated through dispersal from the Tethys into the Germanic Basin, most probably across the Silesian-Moravian or the East Carpathian gates before the late Anisian. This very speciose genus, so far almost restricted to the Middle Triassic, has also been reported from localities in Eastern Switzerland, the Netherlands, Spain, Slovenia, and China. Pending the taxonomic and phylogenetic study of these other material of Eosemionotus, the origin of the genus in the Western or Eastern Tethys remains enigmatic.