{"title":"The inner ear and stapes of the basal mammaliaform Morganucodon revisited: new information on labyrinth morphology and promontorial vascularization","authors":"Simone Hoffmann, Ramza Shahid Malik, Arjun Vidyasagar, Pamela Gill","doi":"10.1093/zoolinnean/zlae062","DOIUrl":null,"url":null,"abstract":"Based on high-resolution computed tomography scanning, we provide new insights into the inner ear and stapedial morphology of Morganucodon from the Early Jurassic of St Brides. At the base of mammaliaforms, Morganucodon plays a pivotal role in understanding the sequence of character acquisition from basal cynodonts to mammals, including the detachment of the middle ear and the evolution of high-frequency hearing. Advancements in imaging technology enabled us to revise or newly describe crucial anatomy that was not accessible for the original description of Morganucodon. Based on 37 petrosals, we can confirm that the apex of the cochlear canal is expanded in Morganucodon, suggestive of a lagena macula. A gently raised crest along the abneural margin is reminiscent of (although much shallower than) the secondary lamina base of other Mesozoic mammaliaforms. The venous circum-promontorial plexus, which surrounded the inner ear in several basal mammaliaforms, was connected to the cochlear labyrinth in Morganucodon through numerous openings along the secondary lamina base. Two petrosals contain fragmentary stapes, which differ substantially from previously described isolated stapes attributed to Morganucodon in having peripherally placed crura and an oval and bullate footplate. Based on the revised stapedial morphology, we question the traditional view of an asymmetrical bicrural stapes as the plesiomorphic condition for Mammaliaformes.","PeriodicalId":49333,"journal":{"name":"Zoological Journal of the Linnean Society","volume":"50 1","pages":""},"PeriodicalIF":3.0000,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Zoological Journal of the Linnean Society","FirstCategoryId":"99","ListUrlMain":"https://doi.org/10.1093/zoolinnean/zlae062","RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ZOOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Based on high-resolution computed tomography scanning, we provide new insights into the inner ear and stapedial morphology of Morganucodon from the Early Jurassic of St Brides. At the base of mammaliaforms, Morganucodon plays a pivotal role in understanding the sequence of character acquisition from basal cynodonts to mammals, including the detachment of the middle ear and the evolution of high-frequency hearing. Advancements in imaging technology enabled us to revise or newly describe crucial anatomy that was not accessible for the original description of Morganucodon. Based on 37 petrosals, we can confirm that the apex of the cochlear canal is expanded in Morganucodon, suggestive of a lagena macula. A gently raised crest along the abneural margin is reminiscent of (although much shallower than) the secondary lamina base of other Mesozoic mammaliaforms. The venous circum-promontorial plexus, which surrounded the inner ear in several basal mammaliaforms, was connected to the cochlear labyrinth in Morganucodon through numerous openings along the secondary lamina base. Two petrosals contain fragmentary stapes, which differ substantially from previously described isolated stapes attributed to Morganucodon in having peripherally placed crura and an oval and bullate footplate. Based on the revised stapedial morphology, we question the traditional view of an asymmetrical bicrural stapes as the plesiomorphic condition for Mammaliaformes.
期刊介绍:
The Zoological Journal of the Linnean Society publishes papers on systematic and evolutionary zoology and comparative, functional and other studies where relevant to these areas. Studies of extinct as well as living animals are included. Reviews are also published; these may be invited by the Editorial Board, but uninvited reviews may also be considered. The Zoological Journal also has a wide circulation amongst zoologists and although narrowly specialized papers are not excluded, potential authors should bear that readership in mind.