Revision of Kyphosichthys grandei Xu & Wu, 2012 from the Middle Triassic of Yunnan Province, South China: implications for phylogenetic interrelationships of ginglymodian fishes

摘要

The hump-backed ginglymodian fish Kyphosichthys grandei, from the Anisian (Middle Triassic) of South China, is re-described. The revised description presents much previously unknown or misidentified anatomical information, such as the presence of a median gular plate; a short, broad, squarish rostral; two pairs of extrascapulars, of which the lateral one is fused with the parietal bone; parasphenoid having relatively large, dorsoposteriorly oriented ascending processes which articulate with the sphenotics; a complete row of scales bordering the body lobe; and supracleithrum with a concave facet for articulation with the posttemporal, etc. Taxonomical comparison clearly distinguishes Kyphosichthys from other known hump-backed ginglymodians - that is, Luoxiongichthys, Lophionotus, Semiolepis and Paralepidotus - and a potential stem-group ginglymodian Dapedium. A more comprehensive cladistic analysis of the Ginglymodi is conducted herein based on incorporation of more morphological characters and taxa, and rectification of the character states of some taxa used in previous analyses after re-description of Kyphosichthys grandei and better knowledge of Luoxiongichthys hyperdorsalis and Sangiorgioichthys sui based on our observations of specimens at the Geological Museum of Peking University, Beijing, China. The results of our analysis produce the most completely resolved and best-supported hypothesis for the monophyletic group Semionotiformes to date, and also support a new hypothesis that the Middle Triassic ginglymodians Luoxiongichthys, Sangiorgioichthys and Kyphosichthys form a monophyletic group at the base of the Ginglymodi, of which Kyphosichthys grandei is the sister group of Sangiorgioichthys sui. The new family Kyphosichthyidae is introduced. The present contribution supplements previous analyses of the Ginglymodi, especially for basal taxa and the clade Semionotiformes, and sheds new light on the origin and early diversification of the Ginglymodi.