Claudiosaurus

Description

Individuals of Claudiosaurus reached a body length of approximately 60 centimetres (2.0 ft). The body form of Claudiosaurus is generally similar to those of other basal diapsids, although the neck of Claudiosaurus is somewhat elongated, with 8 cervical vertebrae, and had a proportionally small head. The body has 16 trunk vertebrae with gastralia present on the underside, and the tail has at least 45 caudal vertebrae. The jaws had numerous small teeth, with the roof of the mouth (palate) being covered in numerous denticles. The sternum is unossified. The pectoral girdle is similar to those of other primitive diapsids. The phalanges of the hands show a reduction of length away from the base, with the exception of the distalmost phalange of the third digit, which is longer than the preceding phalange. The terminal phalanges are flattened. The bones of Claudiosaurus show pachyostosis, suggested to possibly be an adaptation for aquatic life.

Ecology

Claudiosaurus is generally assumed to have been an amphibious animal, using its limbs for propulsion, though it was still likely capable of walking on land, and the skeleton shows only limited adaptations to aquatic life. It has been suggested to have fed on small invertebrates, such as crustaceans.

Classification

Upon its original description, Robert L. Carroll suggested that Claudiosaurus belonged to Sauropterygia (which includes plesiosaurs). Other later studies have generally recovered it as a basal neodiapsid, sometimes as a member of the Younginiformes. Claudiosaurus was recovered as a relative of turtles by Li et al. (2018), forming a clade with the basal neodiapsid Acerosodontosaurus. Although another study in 2020 specifically disputed these conclusions.

Paleoenvironment

The Lower Sakamena Formation was deposited in a wetland environment situated within a North-South orientated rift valley, perhaps similar to Lake Tanganyika. The climate at the time of deposition was temperate, warm, and humid, with seasonal rainfall and possible monsoons. Flora from the formation includes the equisetalean Schizoneura, the glossopterid gymnosperm Glossopteris, and seed fern Lepidopteris. Other vertebrates known from the Lower Sakamena Formation include the palaeoniscoid fish Atherstonia, the procolophonid parareptile Barasaurus, the gliding weigeltisaurid reptile Coelurosauravus, the neodiapsids Hovasaurus, Thadeosaurus, and Acerosodontosaurus, fragments of rhinesuchid temnospondyls, an indeterminate theriodont therapsid and the dicynodont Oudenodon.