Wabanbara ringtailensis—a new chelid turtle (Pleurodira: Chelidae) from mid-Miocene deposits of the Riversleigh World Heritage Area in Australia

The mid-Miocene Ringtail Site of the Riversleigh World Heritage Area in Waanyi country, northwestern Queensland, Australia is a particularly productive locality for chelid turtle fossils. Recently, an almost complete chelid skull was recovered from Ringtail Site. This skull is large and shows a combination of features not found in Australian short-necked chelids: an elongate basisphenoid; large orbits; narrow triturating surface; prominent lateral and posterior emarginations; posteriorly tilted cavum tympani; posteriorly extended squamosal; shallow palate; and a long, broad and ventrally flattened trochlear process. The Ringtail Site skull also differs from Australian long-necked chelids in lacking contact between the quadrate and basisphenoid, possessing unfused frontals, a moderately high temporal arch, and a flattened skull. Aspects of skull morphology suggest that the Ringtail Site chelid was an aquatic omnivore that actively searched for food in open water, and may have employed gape-suction feeding. We designate the Ringtail Site chelid as a new genus and species, and phylogenetically distinct from all modern Australian chelid genera as an early diverging member of the radiation. The Ringtail Site chelid could be closely related to the Australian Miocene taxon Birlimarr gaffneyi—the only other extinct Australian chelid species described from relatively complete skull material. Arthur White [[e-mail]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, Australia, 2052; Anna Gillespie* [[e-mail]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, Australia, 2052; Suzanne Hand [[e-mail]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, Australia, 2052.坐落于澳大利亚昆士兰州西北部瓦尼（Waanyi）领地内的里弗斯利世界遗产地中新世中期环尾遗址，是产出澳龟科（Chelidae）龟类化石的重要化石点。近期，科研人员从环尾遗址中发掘出一具近乎完整的澳龟科龟类头骨。该头骨体型较大，兼具澳大利亚短颈澳龟类所不具备的一系列特征：拉长的基蝶骨（basisphenoid）、宽大的眼眶（orbits）、狭窄的咀嚼面（triturating surface）、显著的侧方与后方切迹、后倾的鼓室腔（cavum tympani）、向后延伸的鳞骨（squamosal）、浅平的腭部，以及修长、宽阔且腹侧扁平的滑车突（trochlear process）。这具环尾遗址头骨还与澳大利亚长颈澳龟类存在差异：方骨（quadrate）与基蝶骨无接触、额骨（frontals）未愈合、颞弓（temporal arch）高度适中，且头骨整体扁平。从头骨形态的诸多特征来看，环尾遗址澳龟属于水生杂食动物，会在开阔水域主动觅食，且可能采用张口抽吸的方式取食。我们将该环尾遗址澳龟确立为全新的属与种，在系统发育上区别于所有现生澳大利亚澳龟类群，属于该演化辐射类群中早期分化的成员。该环尾遗址澳龟可能与澳大利亚中新世类群贝尔利马尔龟（Birlimarr gaffneyi）亲缘关系较近——后者是目前仅有的另一种基于较完整头骨材料被描述的已灭绝澳大利亚澳龟类物种。阿瑟·怀特（Arthur White）[[e-mail]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, Australia, 2052; Anna Gillespie* [[e-mail]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, Australia, 2052; Suzanne Hand [[e-mail]], Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, NSW, Australia, 2052.