Redescription of Sauropsis longimana Agassiz, 1843 from the Upper Jurassic Solnhofen Archipelago (Tithonian, Germany) and the taxonomic diversity of Sauropsis Agassiz, 1832 (Actinopterygii: Pachycormidae)

Pachycormidae is a Mesozoic clade of stem-teleost actinopterygians outside of, but closely related to, Teleostei – the grouping that comprises more than 95% of living fish species and almost half of all extant vertebrate species. The first named pachycormid genus, Sauropsis Agassiz, 1832, is revised based on the historic type species Sauropsis longimanus Agassiz, 1843 from the Upper Jurassic Solnhofen Archipelago of Bavaria. Under the current definition, Sauropsis represents a non-character-based assemblage of historic and ambiguous pachycormid fishes ranging from the Early to Late Jurassic and characterized predominantly by pointed marginal teeth and elongate body shape. Here, we present the first comprehensive description of Sauropsis longimanus and critically review all species previously assigned to Sauropsis. We propose that only the type species, Sa. longimanus, should be retained in Sauropsis, along with a second as yet undescribed species from the Callovian of England. Our revised definition for the genus defines Sauropsis as a small hypsocormine pachycormid with an elongated body (head length = 25% standard length), unpaired fins opposed, with the origin of the dorsal fin very slightly in advance of the anal fin, two or three vertical scale rows per vertebral segment, scales without peg-and-socket articulation, and two independent lateral lines which converge in the supracleithrum. The spelling of Sauropsis longimanus is corrected to Sauropsis longimana to match the gender of the genus following article 31.2 of the International Code of Zoological Nomenclature. A new combination, Simocormus depressus comb. nov., is proposed for a second Upper Jurassic species from Solnhofen, previously described as ‘Sauropsis’ depressus. Phylogenetic analysis resolves Sa. longimana as an early-diverging member of the subfamily Hypsocorminae and sister to the Gondwanan genus Kaykay. We additionally resolve a new unnamed clade of pachycormids containing Simocormus macrolepidotus, Pseudoasthenocormus retrodorsalis and Simocormus depressus comb. nov. that holds an early-diverging position relative to Asthenocorminae + Hypsocorminae, and discuss the evolutionary implications. https://zoobank.org/urn:lsid:zoobank.org:pub:756F6544-0F58-4C4D-B3A0-926AE7251560