page_title: Rhinesuchidae
section_title: Otic notch
hierarchical_section_title: Rhinesuchidae / Description / Otic notch
caption_attribution_description: English: A diagram of the skull of Uranocentrodon senekalensis, a stereospondyl tetrapod from the family Rhinesuchidae. A close-up view of the left otic notch is shown, with colors labeling the characteristic system of otic grooves and ridges which characterize rhinesuchids. The skull used as a template is TM 185, and it is shown in dorsal view Sources: Broom, R. (1930). "Notes on some Labyrinthodonts in the Transvaal Museum"&#160;: Outline of the skull of Uranocentrodon to use as a template. Mariscano et al. (2017). "The Rhinesuchidae and early history of the Stereospondyli (Amphibia: Temnospondyli) at the end of the Palaeozoic"&#160;: Information and imagery on the otic cavity. Eltink et al. (2016)."The cranial morphology of the temnospondyl Australerpeton cosgriffi (Tetrapoda: Stereospondyli) from the Middle-Late Permian of Paraná Basin and the phylogenetic relationships of Rhinesuchidae"&#160;: Information and imagery on the otic cavity.
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: Like most ancient amphibians, rhinesuchids had a pair of indentations at the rear edge of the skull known as otic notches. While sometimes considered to have housed hearing organs such as a tympanum (eardrum), these notches are more likely to have held spiracles, fleshy holes used for breathing. Rhinesuchids can be characterized by a unique system of ridges and grooves within the inner cavity of each otic notch. The walls of the otic notch cavity (sometimes referred to as a tympanic cavity) are mainly made up of the ascending branch of the pterygoid bones. Nevertheless, the inside edge of each cavity is formed by a tabular bone. The tabular bones are a pair of triangular bones along the rear edge of the skull which form pointed structures known as tabular horns. The upper part of the outer wall of the cavity is also formed partly from the squamosal bones, which mostly occupy the flat upper face of the skull. The portion of the squamosal which forms the cavity wall is separated by the portion outside of the cavity by a pronounced boundary known as a falciform crest.
  The outer wall of the cavity has a long and pronounced groove, known as a stapedial groove, which extends lengthwise along the wall. The lower edge of the groove is formed by a ridge/crest known as an oblique ridge, although it has also been called a crista obliqua, otic flange, or simply an oblique crest. The upper edge of the stapedial groove is formed by another ridge/crest bordering the squamosal bone, which Eltink et al. (2016) named the 'dorsal pterygoid crest'. However, Mariscano et al. (2017) preferred to use the name "lamella" for this structure so that it would not be confused with a different ridge present in lydekkerinids, which is sometimes termed an 'oblique crest of the pterygoid', but more commonly called a 'tympanic crest'. Confusingly enough, many rhinesuchids are also known to possess a tympanic crest. This ridge was positioned further back than the other ridges (near the intersection of the pterygoid, quadrate, and squamosal bones) and extends down along the rear face of the cheek. The inner edge of the outer wall of the cavity was formed by a ledge which most studies simply label 'membrane'. This convention exists as a result of the old and likely incorrect hypothesis that otic notches housed eardrums. Under this hypothesis, the inner ledge may have attached to a membrane stretching along the inner cavity of the ear.
  This combination of otic cavity grooves and ridges is unique to rhinesuchids. The lamella and stapedial groove are unknown in any other groups, although they are present in practically every rhinesuchid (except Broomistega, which lacks a lamella). The tympanic crest is present in most rhinesuchids but absent in a few, and it is additionally present in lydekkerinids. The oblique ridge/crest and falciform crest are present in most other sterospondyls (although the former is less well-developed), while the 'membrane' ledge is present in practically every stereospondylomorph.
caption: The skull of Uranocentrodon, with the otic region expanded to show rhinesuchid otic features.
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