The family †Peipiaosteidae contains the genera †Peipiaosteus, †Stichopterus, †Spherosteus, †Yanosteus, and †Liaosteus, all from Late Jurassic to Early Cretaceous deposits of China, Russia, Kazakhstan, and Mongolia. Although the family has taxonomically expanded since it was first established for †P. pani Liu and Zhou, 1965, the amount of detailed comparative data for many of the taxa involved is lacking. In this paper, we describe the osteology of the monotypic genus †Yanosteus from the Yixian Formation (Early Cretaceous) of China largely on the basis of a newly prepared, well-preserved specimen. †Yanosteus is characterized by a series of infraorbital ossicles (a characteristic of the family), a broad, rounded palatopterygoid, a robust dentary, an extremely small opercle and a subopercle with distinctly long and rounded anterior process and a posteriorly scalloped margin, a broad and weakly forked caudal fin, an elongate dorsal fin with more than 160–178 fin rays (diagnostic for the genus), and a short but well-formed pectoral fin spine. We use the results of this study to discuss the characters of the †Peipiaosteioidei and the diversity of †peipiaosteioids.

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