Distinctive emydopoid dicynodont (Therapsida, Anomodontia) mandibles from the Permian Ruhuhu and Usili formations (Songea Group), Ruhuhu Basin, Tanzania

ABSTRACTDicynodont therapsids were discovered in the Permian Usili Formation (Ruhuhu Basin, Tanzania) in the 1930s and in the Permian Ruhuhu Formation in the 1960s, with further collections being made in 2007, 2008, and 2012. Here we describe two fragmentary mandibles that represent a new morphotype of emydopoid dicynodont. One specimen was collected in the middle fossiliferous horizon of the Ruhuhu Formation, and the other originated in the overlying Usili Formation. Three synapomorphies support the placement of these specimens in the emydopoid subclade Kingoriidae: mandibular fenestra occluded by the dentary; curved ridge that follows the profile of the symphysis present on the edge between the anterior and lateral surfaces of the dentary; and posterior dentary sulcus absent. The specimens may represent a new dicynodont species, a previously known species for which mandibular material was unknown, or an intraspecific variant of <i>Dicynodontoides nowacki</i>. Regardless of which of these options is correct, the specimens constitute the first taxon with a stratigraphic range extending from the likely middle Permian middle fossiliferous horizon of the Ruhuhu Formation into the late Permian Usili Formation. They also improve our understanding of the middle Ruhuhu tetrapod fauna, which previously consisted only of <i>Endothiodon tolani</i>.http://zoobank.org/urn:lsid:zoobank.org:pub:E560DB91-177E-4AEC-8379-DBA8F19C5335SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Angielczyk, K. D., and C. B. Cox. 2015. Distinctive emydopoid dicynodont (Therapsida, Anomodontia) mandibles from the Permian Ruhuhu and Usili formations (Songea Group), Ruhuhu Basin, Tanzania. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1008699.

【摘要】二齿兽类（dicynodont）兽孔目（Therapsida）化石最早于1930年代在坦桑尼亚鲁胡胡盆地（Ruhuhu Basin）的二叠纪乌西里组（Usili Formation）被发现，1960年代又于二叠纪鲁胡胡组（Ruhuhu Formation）产出该类群化石，后续分别在2007、2008及2012年开展了多轮化石采集工作。本文记述了两件保存残缺的下颌骨标本，它们代表了一种全新的隐齿兽超科（Emydopoidea）二齿兽形态型。其中一件标本采自鲁胡胡组的中部化石层位，另一件则产自其上覆的乌西里组。三项共源性状（synapomorphies）支持将这两件标本归入金氏兽科（Kingoriidae）：其一，下颌孔（mandibular fenestra）完全被齿骨（dentary）封闭；其二，齿骨前侧面与外侧面的交界处存在一条沿下颌联合（symphysis）轮廓分布的弧形脊；其三，不具备齿骨后沟（posterior dentary sulcus）。该标本群可能代表一个全新的二齿兽物种、一种此前仅知非下颌骨材料的已知物种，或是诺瓦克二齿形兽（<i>Dicynodontoides nowacki</i>）的种内变异类型。无论上述哪种分类方案成立，这两件标本均为首个被发现的地层分布范围覆盖从中二叠世鲁胡胡组中部化石层位到晚二叠世乌西里组的四足动物分类单元。此外，它们也填补了此前鲁胡胡组中部四足动物群仅记录有托兰内四齿兽（<i>Endothiodon tolani</i>）的研究空白，进一步完善了该动物群的物种组成认知。

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本文引用格式：Angielczyk, K. D. 与 C. B. Cox，2015年。《产自坦桑尼亚鲁胡胡盆地二叠纪鲁胡胡组与乌西里组（松盖阿群，Songea Group）的特殊隐齿兽类二齿兽（兽孔目，异齿亚目，Anomodontia）下颌骨》。《脊椎动物古生物学杂志（*Journal of Vertebrate Paleontology*）》。DOI: 10.1080/02724634.2015.1008699。