page_title: Rhinesuchidae
section_title: Classification
hierarchical_section_title: Rhinesuchidae / Classification
caption_attribution_description: Australerpeton cosgriffi
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: When the family was first named in 1919, Rhinesuchidae was already recognized as a group of basal stereospondyls, a position which it retains even in the present day. Among the traits used to support this position include the fact that most rhinesuchids had long anterior branches of their pterygoids. More advanced stereospondyls had shorter anterior branches. In 1947, Alfred Romer placed the family (which he believed only included Rhinesuchus) in a broad superfamily which he called Rhinesuchoidea. Rhinesuchoidea was intended to be part of an evolutionary grade of temnospondyls linking "primitive" rhachitomes such as Eryops to "advanced" stereospondyls such as metoposaurs and trematosaurs. This grade, termed "neorhachitomes", was separated into Capitosauroidea (which contained capitosaurs and "benthosuchids") and Rhinesuchoidea. Apart from containing Rhinesuchidae, Rhinesuchoidea also contained various genera as well as the families Lydekkerinidae, Sclerothoracidae, and finally Uranocentrodontidae. Romer felt that certain taxa (i.e. Uranocentrodon and the possibly synonymous dubious genus "Laccocephalus") often considered rhinesuchids were best placed in the separate family Uranocentrodontidae, while others (i.e. Rhinesuchoides) were not placed in any rhinesuchoid family in particular. Other families were later placed in this Rhinesuchoidea, such as Rhinecepidae in 1966 and Australerpetonidae in 1998.
  The arrival of cladistics in the late 20th century has caused grades to fall out of favor in recent years, replaced by clades, which are defined by close relations rather than ancestral assemblages. However, the basic idea behind Rhinesuchoidea, which states that advanced stereospondyls descended from animals similar to rhinesuchids, is still considered valid. Rhinecepidae and Uranocentrodontidae were found to be synonymous with Rhinesuchidae according to a 2000 analysis by Schoch and Milner. One study placed Rhinesuchidae within the superfamily Capitosauroidea. However, this interpretation has not been followed by other studies which consider rhinesuchids to be more basal than capitosaurs. Australerpetonidae, a monotypic family only containing the genus Australerpeton, has been more difficult to compare to Rhinesuchidae. Some studies place Australerpeton as a basal stereospondyl outside of Rhinesuchidae, while others consider it an archegosaurid outside of Stereospondyli entirely.
  A comprehensive review of Australerpeton published by Eltink et al. (2016) favored the hypothesis that it was deeply nested within Rhinesuchidae. A phylogenetic study performed as part of the study split the family into two clades. One clade was a subfamily termed Rhinesuchinae. Rhinesuchinae contains Rhinesuchus and Rhineceps. This subfamily is mainly characterized by features of the palate, such as an anterior branch of the pterygoid lacking ridges and palatine bones covered in tiny denticles. The other main clade of the family contained Uranocentrodon as well as another subfamily termed Australerpetinae. This clade is united by the presence of a tympanic crest and a foramen magnum (the hole for the spinal cord at the back of the braincase) which has a curved upper edge. Australerpetinae is a modified version of Australerpetonidae which has been reduced to subfamily status in order to fit within Rhinesuchidae. This subfamily contains Australerpeton, Broomistega, Laccosaurus, and Rhinesuchoides. Members of this subfamily had somewhat longer and more tapered snouts than other Rhinesuchids, although (according to Eltink et al..) their pterygoids had short anterior branches, letting the palatine bones contact the interpterygoid vacuities. The most parsimonious (evolutionarily simplest) tree found by Eltink et al. (2016) is seen below:
  The structure of Rhinesuchidae following Eltink et al.'s study was challenged by a different study on rhinesuchids published less than a year later. This study, Mariscano et al.. (2017), agreed that Australerpeton was a rhinesuchid, but considered it the most basal member of the family. They disagree with Eltink et al.
caption: Australerpeton, a long-snouted putative member of the family
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