Chroniosaurus dongusensis (Tverdokhlebova 1972) Early Permian ~7 cm skull length, was considered an aberrant pre-reptile by all prior workers, but here it nests within the Archosauromorpha. Derived from a sister to Solenodonsaurus, Chroniosaurus was a sister to Chroniosuchus.

Distinct from Solenodonsaurus, Chroniosaurus had a longer rostrum, a longer premaxilla, a longer naris and an antorbital fenestra. A medial fenestra separated the premaxillae and anterior vomers. A distinct otic notch is present, similar to that of Solenodonsaurus, Oedaleops, Tetraceratops, Silvanerpeton and Gephyrostegus. The teeth were smaller and more widely spaced. The rear of the skull did not have such a steep anterior lean. No interpterygoid vacuity separated the pterygoids. The internal nares were displaced to the margins by extension and expansion of the vomers and palatines.

The clavicle extended above the scapula. The humerus was not much longer than the radius.

A set of ossified plates lined the back, each one sliding under its predecessor during undulation and offering both support and protection.

Other chronisuchid skulls may be 25 cm in length.

Chroniosaurus (?) (THUg 3308 and PIN 3585/124, Clack and Klembara 2009), apparently dissimilar in appearance (judging by the figures) and if so, worthy of its own generic name. ~25 cm in preserved length.

Distinct from the holotype, the naris and internarial fenestra were smaller. The jawline was convex ventrally. The orbit was taller rand raised above the rostral margin. The quadrate leaned further anteriorly. The mandible was shallower. The vomer teeth were long and nail-like.

Distinct from Solenodosaurus, each vertebra was composed of three unfused elements, the neural arch, pleurocentrum and intercentrum in proportions resembling those of pre-reptiles (primitive tetrapods), like Proterogyrinus. This is a reversal and likely a product of the smaller size of chroniosuchians. The first four caudal vertebrae included bent-back ribs that all terminated at the fifth caudal.

The interclavicle was larger. Distinct fromLimnoscelis., but similar to Solenodonsaurus, the humerus had a simple shape, narrow proximally, wide distally.

The ilium had an elongated posterior process and a minor anterior process, as in Limnoscelis. The tarsus was poorly ossified and composed of round elements, all suggestive of an entirely aquatic, bottom-dweller lifestyle.

Buchwitz M and Voigt S 2010. Peculiar carapace structure of a Triassic chroniosuchian implies evolutionary shift in trunk flexibiliy. Journal of Vertebrate Paleontology30(6):1697-1708.

Clack JA and Klembara J 2009. An articulated specimen of Chroniosaurus dongusensis and the morphology and relationships of the chroniosuchids. Special Papers in Palaeontology, 81: 15–42.

Klembara J, Clack J, and Cernansky A 2010. The anatomy of palate of Chroniosaurus dongusensis (Chroniosuchia, Chroniosuchidae) from the Upper Permian of Russia. Palaeontology 53: 1147-1153.

Schoch RR, Voig S and Buchwitz M 2010. A chroniosuchid from the Triassic of Kyrgyzstan and analysis of chroniosuchian relationships. Zoological Journal of the Linnean Society 160: 515–530. doi:10.1111/j.1096-3642.2009.00613.x

Tverdochlebova GI 1972. A new Batrachosaur Genus from the Upper Permian of the South Urals, Paleontol. Zh., 1972: 95–103.

hwiki/Chroniosaurus