A Revision of Middle Jurassic Hybodus houtienensis Young (Chondrichthyes: Hybodontidae) from Yunnan.

Summary: Hybodus houtienensis Young was a fossil shark erected by C. C. Young in 1941 according to two pieces of fin spines found in the Upper Lufeng Series in the Lufeng basin, Yunnan. The rock yielding the fishes was assigned to the Late Triassic, and is reassigned to the Middle Jurassic recently (Fang et al., 2000; Cheng et al., 2004). The new material described here was found in the Laoluocun Formation of the Laochangjing-Dajianshan section, Chuanjie Town, Lufeng County, Yunnan. Hybodus was mainly found in marine sediments, but in China, apart from the two species H. zuodengensis and H. yohi that were recognized as conodonts (Wang et al., 2001), all others were found in continental or continent-related deposits. H. houtienensis was found in red beds, which are clearly continental deposits.Systematic paleontologyChondrichthyes Huxley 1880 Euselachii Hay 1902 Hybodontidae Owen 1846 Hybodus Agassiz 1837Type species Hybodus reticulatus Agassiz, 1837 Hybodus houtienensis Young, 1941 (Fig. 1A; Pl. 1, figs.1-4)1941 Hybodus houtienensis Young, Pl.1, figs. 1-2.Etymology: houtien, Chinese phonetic characters for the locality where the fossil was first discovered.Syntype: GMV633-1,2,two incomplete spines (i.e. V16 and V18 of Young, 1941, Pl.1, fig. 1). Young (1941) did not assign a holotype for the species, so here these two specimens are recognized as a syntype of this species.Plesiotype: GMV2100, a nearly complete tooth.Locality and horizon: Anning and Lufeng counties, Yunnan; Middle Jurassic Laoluocun Formation.Diagnosis Asymmetric clutching type tooth with cusps reaching 6 in number. The labial face of the tooth has developed ridge ornaments. The principal cusp has a height of about half of the tooth breadth and a main ornament ridge up to its top while the ridges in the right wing of the cusp intersect with the main ridge. The dorsal spine is strong, with long irregular ridge ornaments and tubercles at the surface. Remarks Hybodus houtienensis can be clearly distinguished from the other Hybodus found in China in the size and shape of its tooth. It is similar to H. yohi, which was recognized as a conodont, in the asymmetrical type tooth, but greatly different in the tooth size and the proportion of the cusps. It is most similar to the type species, Hybodus reticulatus Agassiz, and only different in the ornaments and the number of cusps in teeth.