Re-description of the sexually dimorphic peltopleuriform fish Wushaichthys exquisitus (Middle Triassic, China): taxonomic implications and phylogenetic relationships

Wushaichthys exquisitus, a small fish from the Ladinian of Xingyi, Guizhou Province, southern China, was named a few years ago and interpreted as the most primitive species in the Thoracopteridae (Triassic 'flying' fishes with a Euro-Asian distribution). However, this hypothesis was questioned, because Wushaichthys also shares features with Peltopleuridae. A detailed morphological re-description of Wushaichthys was conducted based on new specimens, plus a revision of previously studied ones, as well as of members of Peripeltopleurus and thoracopterids, and their relationships were tested with a phylogenetic analysis based on 137 characters and 54 taxa. The results suggest that Wushaichthys is a member of a Glade that is interpreted here as the new superfamily Thoracopteroidea, which contains Wushaichthyidae fam. nov. (Wushaichthys Peripeltopleurus) and Thoracopteridae and is the sister taxon of the nonmonophyletic Peltopleuridae among Peltopleuriformes. Thoracopteroidea superfam. nov. is strongly supported by numerous synapomorphies (e.g. frontal (= parietal) bone slightly expanded laterally; posttemporal contacts the extrascapular anterolaterally separating it from its counterpart; suspensorium is vertically oriented; narrow and deep rectangular preopercle, vertically oriented; preopercle sutured with the rear edge of the maxilla throughout the maxillary process; enlarged pectoral fins in most genera; and deeply forked hypocercal caudal fin). Although Thoracopteridae is monophyletic, one of its genera, Thoracopterus, is not. Consequently, the content of Thoracopteridae was re-evaluated and now includes Thoracopterus, Gigantopterus, Potanichthys comb. nov. and Italopterus gen. nov. Wushaichthyidae is supported by a unique combination of characters, and the results confirm it as a thoracopteroid, but not a thoracopterid. The characters of Wushaichthys are relevant for understanding the taxonomy and systematics of thoracopteroids, especially the evolutionary morphological modifications of the pectoral and pelvic fins and the lower lobe of the caudal fin, which are some of the main characters of these fishes.

Automated summary

A detailed morphological re-description and phylogenetic analysis revealed that Wushaichthys is a member of the new superfamily Thoracopteroidea, as part of the newly proposed Wushaichthyidae fam. nov. The study confirmed Wushaichthys as a thoracopteroid, but not a thoracopterid, significantly contributing to the understanding of the taxonomy and systematics of thoracopteroids.