Claudiosaurus

Claudiosaurus is known from the Sakamena Formation of Madagascar. Claudiosaurus is found from the Late Permian. Although a paper mentions that they have been also found in Early Triassic deposits of Madagascar,[1] citation does not mention that Claudiosaurus is from Triassic.[2]

Size compared to human hand

Inidividuals of Claudiosaurus reached a body length of approximately 60 centimetres (2.0 ft).[3] 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.[4] The sternum is unossified.[5] The pectoral girdle is similar to those of other primitive diapsids.[6] 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 preceeding phalange. The terminal phalanges are flattened.[4] The bones of Claudiosaurus show pachyostosis, suggested to possibly be an adaptation for aquatic life.[7]

Life restoration of Claudiosaurus germaini

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.[4]

Upon its original description, Robert L. Carroll suggested that Claudiosaurus belonged to Sauropterygia (which includes plesiosaurs).[4] Other later studies have generally recovered it as a basal neodiapsid, sometimes as a member of the Younginiformes.[8][9] Claudiosaurus was recovered as a relative of turtles by Li et al. (2018), forming a clade with the basal neodiapsid Acerosodontosaurus.[10] Although another study in 2020 specifically disputed these conclusions.[11]

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.[12] 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 Acerodontosaurus, fragments of rhinesuchid temnospondyls, an indeterminate theriodont therapsid and the dicynodont Oudenodon.[13]

• Caldwell, Michael W. (1995). "Developmental Constraints and Limb Evolution in Permian and Extant Lepidosauromorph Diapsids". Journal of Vertebrate Paleontology. 14 (4): 459–471. Bibcode:1995JVPal..14..459C. doi:10.1080/02724634.1995.10011572. JSTOR 4523588.
• Carroll, R. L. (1981). "Plesiosaur ancestors from the Upper Permian of Madagascar". Philosophical Transactions of the Royal Society. B. 293 (1066): 315–383. Bibcode:1981RSPTB.293..315C. doi:10.1098/rstb.1981.0079.
• Sues, Hans-Dieter (2019). The Rise of Reptiles: 320 Million Years of Evolution. Johns Hopkins University Press. doi:10.1353/book.67468. ISBN 978-1-4214-2868-0.
• Cuthbertson, Robin S.; Russell, Anthony P.; Anderson, Jason S. (July 2013). "Cranial morphology and relationships of a new grippidian (Ichthyopterygia) from the Vega-Phroso Siltstone Member (Lower Triassic) of British Columbia, Canada". Journal of Vertebrate Paleontology. 33 (4): 831–847. Bibcode:2013JVPal..33..831C. doi:10.1080/02724634.2013.755989. JSTOR 42568652. S2CID 131501541.
• "Stomach stones for feeding or buoyancy? The occurrence and function of gastroliths in marine tetrapods". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences. 341 (1296): 163–175. 29 July 1993. doi:10.1098/rstb.1993.0100.