fossil record; however, without the proper soft tissue impressions this is nothing more than an assumption. The earliest discovery of a burrowing Thrinaxodon places the specimen found around 251 million years ago, a time frame surrounding the Permian–Triassic extinction event. Much of these fossils had been found in the flood plains of South Africa, in the Karoo Basin. This behavior had been seen at a relatively low occurrence in the pre-Cenozoic, dominated by therapsids, early-Triassic cynodonts and some early Mammalia. Thrinaxodon was in fact the first burrowing cynodont that has been found, showing similar behavioral patterns to that of Trirachodon. The first burrowing vertebrate on record was the dicynodont synapsid Diictodon, and it is possible that these burrowing patterns had passed on to the future cynodonts due to the adaptive advantage of burrowing during the extinction. The burrow of Thrinaxodon consists of two laterally sloping halves, a pattern that has only been observed in burrowing non-mammalian Cynodontia. The changes in vertebral/rib anatomy that arose in Thrinaxodon permit the animals to a greater range of flexibility, and the ability to place their snout underneath their hindlimbs, an adaptive response to small living quarters, in order to preserve warmth and/or for aestivation purposes. A Thrinaxodon burrow contained an injured temnospondyl, Broomistega. The burrow was scanned using a synchrotron, a tool used to observe the contents of the burrows in this experiment, and not damage the intact specimens. The synchrotron revealed an injured rhinesuchid, Broomistega putterilli, showing signs of broken or damaged limbs and two skull perforations, most likely inflicted by the canines of another carnivore. The distance between the perforations was measured in relation to the distance between the canines of the Thrinaxodon in question, and no such relation was found. Therefore, we may assume that the temnospondyl found refuge in within the burrow after a traumatic experience and the T. liorhinus allowed it to stay in its burrow until they both ultimately met their respective deaths. Interspecific shelter sharing is a rare anomaly within the fossil record, this T. liorhinus shows one of the first occurrences of this type of behavior in the fossil record, and, however, we are currently unsure if the temnospondyl inhabited the burrow before or after the death of the nesting Thrinaxodon. See also List of therapsids References Further reading 69. 202–203. Prehistoric cynodont genera Early Triassic synapsids of Africa Triassic South Africa Fossils of South Africa