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Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the UK', Journal of Vertebrate Paleontology

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Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the UK', Journal of Vertebrate Paleontology Edinburgh Research Explorer A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the UK Citation for published version: Panciroli, E, Walsh, S, Fraser, N, Brusatte, S & Corfe, I 2017, 'A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the UK', Journal of Vertebrate Paleontology. https://doi.org/10.1080/02724634.2017.1351448 Digital Object Identifier (DOI): 10.1080/02724634.2017.1351448 Link: Link to publication record in Edinburgh Research Explorer Document Version: Publisher's PDF, also known as Version of record Published In: Journal of Vertebrate Paleontology General rights Copyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 10. Oct. 2021 Journal of Vertebrate Paleontology ISSN: 0272-4634 (Print) 1937-2809 (Online) Journal homepage: http://www.tandfonline.com/loi/ujvp20 A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom Elsa Panciroli, Stig Walsh, Nicholas C. Fraser, Stephen L. Brusatte & Ian Corfe To cite this article: Elsa Panciroli, Stig Walsh, Nicholas C. Fraser, Stephen L. Brusatte & Ian Corfe (2017): A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2017.1351448 To link to this article: http://dx.doi.org/10.1080/02724634.2017.1351448 © 2017 The Author(s). Published with Published online: 12 Sep 2017. license by the Society of Vertebrate Paleontology© Elsa Panciroli, Stig Walsh, Nick Fraser, Stephen L. Brusatte, and Ian Corfe. Submit your article to this journal Article views: 556 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ujvp20 Download by: [The University of Edinburgh] Date: 17 October 2017, At: 03:11 Journal of Vertebrate Paleontology e1351448 (20 pages) Published with license by the Society of Vertebrate Paleontology DOI: 10.1080/02724634.2017.1351448 ARTICLE A REASSESSMENT OF THE POSTCANINE DENTITION AND SYSTEMATICS OF THE TRITYLODONTID STEREOGNATHUS (CYNODONTIA, TRITYLODONTIDAE, MAMMALIAMORPHA), FROM THE MIDDLE JURASSIC OF THE UNITED KINGDOM ELSA PANCIROLI, *,1,2 STIG WALSH,1,2 NICHOLAS C. FRASER, 1,2 STEPHEN L. BRUSATTE,1,2 and IAN CORFE3 1School of Geosciences, University of Edinburgh, Grant Institute, Kings Buildings, Edinburgh EH9 3FE, United Kingdom, [email protected]; [email protected]; 2National Museum of Scotland, Chambers Street, Edinburgh EH1 1JF, United Kingdom, [email protected]; [email protected] 3Jernvall EvoDevo Laboratory, Institute of Biotechnology, University of Helsinki, P.O. Box 56, FIN-00014 Helsinki, Finland, ian.corfe@helsinki.fi ABSTRACT—Tritylodontidae was a successful advanced cynodont clade with a close relationship to mammals, but falling outside the clade Mammaliaformes. Stereognathus ooliticus was the first tritylodontid to be named and described in 1854, but since then no comprehensive description for this species has been produced. A second species, S. hebridicus, was named in 1972 and diagnosed based solely on size difference, being larger than the S. ooliticus holotype. We reexamined all postcanine tooth material attributed to the genus Stereognathus to test the species diagnosis and identify diagnostic morphological characters for this genus. We find no statistical difference in size distribution between S. ooliticus and S. hebridicus postcanine specimens. Specimens previously attributed to the different species fall along an ontogenetic spectrum of size, with no clear clustering. Morphologically, we affirm many previously described features for Stereognathus and identify new morphological features in upper and lower postcanines. We find no morphological features to distinguish these two species, and therefore we synonymize S. hebridicus under S. ooliticus. We reevaluate the scoring of S. ooliticus in previous phylogenetic analyses, generating a new tree using rescored Stereognathus characters. Finally, we suggest that similar reevaluations and redescriptions of other poorly described tritylodontid material are necessary to further clarify relationships among Tritylodontidae and the evolution of characters in derived genera such as Stereognathus. Citation for this article: Panciroli, E., S. Walsh, N. C. Fraser, S. L. Brusatte, and I. Corfe. 2017. A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1351448. INTRODUCTION persisting into the Early Cretaceous (Maisch et al., 2004; Hu Tritylodontids are advanced cynodont mammaliamorphs that et al., 2009; Matsuoka et al., 2016). Although they shared many fall outside the clade Mammaliaformes, but their close relation- cranial and postcranial features with early mammaliaforms, they ship to mammals is now generally accepted (Rowe, 1993; Luo retained a quadrate-articular jaw joint, lacked a dentary-squamo- et al., 2002; Ruta et al., 2013). Superficially, tritylodontids would sal contact, and they had a large angular process and a large have appeared rodent-like: enlarged procumbent incisors coronoid process on the dentary (Kemp, 2005). Their size range replaced the absent canine teeth, they possessed a diastema, and and specializations for herbivory are among the characteristics their postcanine teeth were highly specialized for herbivory. that distinguish them from many of the early mammals they lived Downloaded by [The University of Edinburgh] at 03:11 17 October 2017 Tritylodontids ranged in size from genera such as Bocatherium alongside (Kemp, 2005). < at 5 cm skull length (Clark and Hopson, 1985) to larger genera Tritylodontidae currently includes over 17 genera (with at > with 22 cm skull lengths, such as Kayentatherium (Kermack, least five more genera debated or synonymized) and have been 1982). They were the last surviving family of non-mammaliaform described from Africa (Owen, 1884; Fourie, 1963), Antarctica cynodonts, appearing in the fossil record in the Late Triassic (Lewis, 1986; Hammer and Smith, 2008), Asia (Young, 1940, (Hennig, 1922; Fedak et al., 2015), living alongside early mam- 1982; Chow and Hu, 1959; Cui, 1976, 1981; He and Cai, 1984; mals and other mammaliaforms throughout the Jurassic and Luo and Sun, 1994; Matsuoka and Setoguchi, 2000; Maisch et al., 2004; Watabe et al., 2007; Lopatin and Agadjanian, 2008; Hu et al., 2009; Matsuoka et al., 2016; Velazco et al., 2017), Europe *Corresponding author. (Charlesworth, 1855; Owen, 1857; Hennig, 1922; Waldman and Ó Elsa Panciroli, Stig Walsh, Nick Fraser, Stephen L. Brusatte, and Savage, 1972; Ensom, 1977, 1994), and North America Ian Corfe. (Kermack, 1982; Sues, 1985, 1986; Sues and Jenkins, 2006; Fedak This is an Open Access article distributed under the terms of the Crea- et al., 2015), including Mexico (Clark and Hopson, 1985). All are tive Commons Attribution-NonCommercial-NoDerivatives License considered herbivorous (Kuhne,€ 1956; Sues, 1986), except (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non- Yuanotherium minor, which was described as having dental char- commercial re-use, distribution, and reproduction in any medium, pro- vided the original work is properly cited, and is not altered, transformed, acteristics that suggest that it may have been omnivorous (Hu or built upon in any way. et al., 2009). Color versions of one or more of the figures in the article can be found Stereognathus was the first tritylodontid genus named and online at www.tandfonline.com/ujvp. identified (Charlesworth, 1855). Since that time, material from Panciroli et al.—Reassessment of postcanine dentition and systematics of Stereognathus (e1351448-2) across the U.K. has been assigned to Stereognathus, and its The oldest microvertebrate site to yield Stereognathus material name appears regularly on faunal lists. However, the anatomy is Hornsleasow Quarry, part of the Chipping Norton Limestone and taxonomy of this genus remain poorly understood. Two Formation: it is early Bathonian and is a Site of Special Scientific species have been described: the type species S. ooliticus Char- Interest (SSSI) because it preserves a complete succession of lesworth, 1855, is currently represented by hundreds of cusp Sharp’s Hill Beds (Metcalf et al., 1992). Material comes from a fragments and at least 48 somewhat more complete postcanine productive clay lens, likely formed in a fresh to brackish
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