A Late Jurassic freshwater shark assemblage (Chondrichthyes, Hybodontiformes) from the southern Junggar Basin, Xinjiang, Northwest China

A low-diversity hybodont assemblage from the Late Jurassic (Oxfordian) Qigu Formation at Liuhuanggou in the southern Junggar Basin includes the remains of three taxa based on isolated teeth, two of which represent new species of a hitherto unknown genus: Hybodus sp. cf. H . huangnidanensis Wang, 1977, Jiaodontus montaltissimus gen. et sp. nov., and Jiaodontus vedenemus gen. et sp. nov. H. sp. cf. H . huangnidanensis might represent a new taxon pending future revisions. The two new species of Jiaodontus gen. nov. are assigned to the Lonchidiidae and represent endemic species, which are only known from the Junggar Basin. Their teeth superficially resemble those of other lonchidiids, such as Parvodus and Vectiselachos , but differ in several aspects, including the morphology of the cusp and cusplets and the ornamentation pattern. Two different morphotypes of dermal denticles with hybodont affinities, possibly representing two species, are described. The low enameloid δ 18 O PO4 values [9.7 ± 0.4‰ (standard deviation), n = 5) of H. sp. cf. H . huangnidanensis teeth indicate that at least this taxon was completely adapted to freshwater. This is in good accordance with the depositional setting and sedimentological results.