Cretaceous soft-shelled turtles (Trionychidae) of Mongolia: new diversity, records and a revision

<div><p>This paper is devoted to the description and revision of material of Cretaceous soft-shelled turtles (Trionychidae) of Mongolia. It includes the description of seven trionychid species, six of which are new, and two new genera: the cyclanorbine <i>Nemegtemys conflata</i> gen. et sp. nov. from the Nemegt Formation (Maastrichtian), and the trionychines <i>Gobiapalone breviplastra</i> gen. et sp. nov. from the Nemegt and Barungoyot (Campanian) formations, <i>G. orlovi</i> from the Baynshire Formation (Cenomanian–Santonian), ‘<i>Trionyx</i>’ <i>baynshirensis</i> sp. nov. from the Baynshire Formation, ‘<i>T</i>.’ <i>gilbentuensis</i> sp. nov. from the Nemegt Formation, ‘<i>T</i>.’ <i>gobiensis</i> sp. nov. from the Nemegt Formation, and ‘<i>T</i>.’ <i>shiluutulensis</i> sp. nov. from an unknown formation (Campanian). In addition, one shell from the ?Baynshire Formation of Khermin Tsav is assigned to <i>Gobiapalone</i> sp. The type material of <i>Amyda menneri</i> is considered to be Trionychidae indet. and <i>Amyda menneri</i> to be a nomen dubium. Finally, we revise other available materials of Cretaceous trionychids from 45 localities in Mongolia. <i>Nemegtemys conflata</i>, if correctly assigned, is the earliest known member of Cyclanorbinae. The two species of the new genus <i>Gobiapalone</i> are included in two phylogenetic analyses of Trionychidae. In both analyses <i>Gobiapalone</i> is monophyletic. In the first analysis, <i>Gobiapalone</i> is placed within Apalonina. In the second analysis, <i>Gobiapalone</i> is sister to Apalonina. Thus, the results of both analyses show that Apalonina, which is a rather advanced and well-supported trionychid clade, or its closest sister taxon (stem-Apalonina), were present in the Late Cretaceous of Asia. These results suggest that most other supra-generic clades of modern trionychids had been established in Asia by the Late Cretaceous. That suggestion is supported by the discovery of a cyclanorbine <i>Nemegtemys conflata</i> in the Late Cretaceous of Mongolia. Finally we summarize the latest data on temporal and geographical distributions of Cretaceous Trionychidae of Asia and North America.</p><p></p></div>