The tetrapod fauna of the upper Permian Naobaogou Formation of China: 7. Laosuchus hun sp. nov. (Chroniosuchia) and interrelationships of chroniosuchians.

Chroniosuchians were the only clade of non-amniotic reptiliomorphs that survived into the Triassic. Recent discoveries have increased their species and anatomical diversity and expanded their distribution in time and space. Most species were represented only by osteoderms, and complete or articulated remains are rare. Here we report a partial skull with a mandible and associated postcranial skeleton from the Naobaogou Formation in the Daqingshan, Nei Mongol, China. It is referred to Laosuchus based on the absence of a preorbital fenestra, the presence of a well-developed transverse flange of the pterygoid that contacts the maxilla, an internal crest on and above the dorsal side of the palate (vomer, ectopterygoid and pterygoid), a shallow otic notch formed by the tabular horn and the posterior part of the squamosal, a thin and high ventromedial ridge on the parasphenoid; the surangular dorsal surface forming a fossa for the insertion of the external adductors, the maxilla and quadratojugal separated by the jugal, and a jugal with a ventral (alary) process bordering the subtemporal fenestra. A new species, L. hun, is established based on its palatal dentition that is reduced, with but a few denticles on the vomer and pterygoid, and an irregular posterior cheek margin. Laosuchus can be referred to Chroniosuchidae based on cranial features, and the divergence of the Chroniosuchidae and Bystrowianidae is confirmed in this study. New findings reinforce the hypothesis of the migration route from North China to Laos in the late Permian. [ABSTRACT FROM AUTHOR]