page_title: Rhinesuchidae
section_title: Paleobiology
hierarchical_section_title: Rhinesuchidae / Paleobiology
caption_attribution_description: English: Upper-side 3D rendering of the content inside the burrow cast BP/1/5558 in semi-transparency.Thrinaxodon liorhinus (in brown; BP/1/7199) is lying on its ventral side; Broomistega putterilli (in grey; BP/1/7200) deposited upside down on the right side of the Thrinaxodon.
context_page_description: Rhinesuchidae is a family of tetrapods that lived primarily in the Permian period. They belonged to the broad group Temnospondyli, a successful and diverse collection of semiaquatic tetrapods which modern amphibians are probably descended from. Rhinesuchids can be differentiated from other temnospondyls by details of their skulls, most notably the interior structure of their otic notches at the back of the skull. They were among the earliest-diverging members of the Stereospondyli, a subgroup of temnospondyls with flat heads and aquatic habits. Although more advanced stereospondyls evolved to reach worldwide distribution in the Triassic period, rhinesuchids primarily lived in the high-latitude environments of Gondwana during the Guadalupian and Lopingian epochs of the Permian. The taxonomy of this family has been convoluted, with more than twenty species having been named in the past; a 2017 review recognized only eight of them to be valid. While several purported members of this group have been reported to have lived in the Triassic period, most are either dubious or do not belong to the group.
context_section_description: Most rhinesuchids are only known from skull material, although a few members of the group (Uranocentrodon, Broomistega, and Australerpeton, for example) include specimens preserving a significant portion of the rest of the skeleton. A juvenile specimen of Broomistega had ankles and vertebrae which were poorly ossified, indicating that its joints had a large amount of cartilaginous material to supplement the low amount of bone. This trait is often correlated with an aquatic lifestyle. Features of the skull, such as upwards-pointing eyes, also support this hypothesis.
  Despite this support for an aquatic lifestyle, other pieces of evidence show that rhinesuchids were capable of some terrestrial movement. Although rhinesuchids did not possess any adaptations for digging, the poorly-ossified juvenile specimen of Broomistega was found in a flooded burrow which was also inhabited by a Thrinaxodon. Various conditions of the way these animals were preserved indicate that they co-inhabited the burrow peacefully, likely to survive a drought by aestivating (staying in a dormant state during hot and dry conditions). The fact that a Broomistega was able to enter the burrow of a terrestrial animal such as Thrinaxodon indicates that rhinesuchids were not exclusively aquatic.
  In addition, it has been noted that larger temnospondyls generally have more well-ossified joints. For example, large specimens of Australerpeton possessed robust hips, several completely bony ankle bones, and ossified pleurocentra (part of the vertebrae). Nevertheless, these skeletons were not as strongly built as those of Eryops (a supposedly terrestrial temnospondyl), with smaller shoulder girdles and less prominent sites for muscle attachment. Dias & Schultz (2003) suggested that the lifestyle of Australerpeton (and presumably other rhinesuchids) was that of a semiaquatic piscivore (fish-eater), preferring to hunt in shallow bodies of freshwater yet retaining the ability to walk on land during droughts.
  A Histological study of several indeterminate rhinesuchid fossils (referred to Rhinesuchus) indicate that members of the family grew seasonally, as in modern amphibians. Individuals also had fairly long life span, with one specimen being 30 to 35 years old at the time of its death based on the number of lines of arrested growth (rings in the bone used to tell age, like tree rings) present in a hip fragment. Some lines of arrested growth were very narrow, indicating that the individuals could reduce their growth and metabolism during times of hardship. This ability may be the reason why rhinesuchids were rather successful at the end of the Permian, as well as how a few small members of the group survived the Permian-Triassic extinction event.
caption: Broomistega (green) preserved in a fossilized burrow with Thrinaxodon (brown)
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