The postcranial skeleton of <i>Galecyon</i>: evidence for morphological and locomotor diversity in early Hyaenodontidae (Mammalia, Hyaenodontida)

ABSTRACTHyaenodontidae is a diverse component of the carnivorous guild in early Eocene (Wasatchian) North American mammalian faunas. Although there have been suggestions that early members of the family had diverse locomotor repertoires, few Wasatchian postcrania are adequately described. Here we describe the first known postcranial remains of the rare Wasatchian hyaenodontid <i>Galecyon</i>, based principally on a well-preserved partial skeleton from the Willwood Formation, Wyoming. <i>Galecyon</i> is reconstructed as a 5.2–7.9 kg terrestrial carnivore. Small but significant differences throughout the skeleton distinguish <i>Galecyon</i> from <i>Prolimnocyon</i>. <i>Galecyon</i> is reconstructed as scansorial/generalized terrestrial because these postcranial differences consistently indicate a more terrestrial habit than in the scansorial <i>Prolimnocyon</i>. Among other hyaenodontids, <i>Arfia</i> shows evidence for parallel terrestrial adaptation, whereas <i>Pyrocyon</i> is morphologically intermediate between <i>Galecyon</i> and <i>Prolimnocyon</i>. Manipulation of the well-preserved bones forming the crurotarsal joint of <i>Galecyon</i> provides evidence that contradicts a previous proposal that <i>Arfia</i>, another Wasatchian hyaenodontid, was capable of hind foot reversal. In both genera, movements at the crurotarsal joint were largely restricted to a parasagittal plane. Phylogenetic analysis of a new postcranial character set supports a pattern of relationships for early Eocene hyaenodontids different from that supported by dental morphology. Combining the two data partitions favors most aspects of the dental topology, but the conflict between dental and postcranial data indicates that confident phylogenetic resolution can be elusive, even with relatively dense sampling. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Zack, S. P., and K. D. Rose. 2015. The postcranial skeleton of <i>Galecyon</i>: evidence for morphological and locomotor diversity in early Hyaenodontidae (Mammalia, Hyaenodontida). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2014.1001492.摘要：鬣齿兽科（Hyaenodontidae）是始新世早期（瓦萨奇期）北美哺乳动物群中食肉动物生态类群的多样性组成部分。尽管学界曾提出该科早期类群拥有多样的运动模式，但目前针对瓦萨奇期颅后骨骼（Postcrania）的充分描述仍较为匮乏。本研究基于产自怀俄明州威尔伍德组一具保存完好的部分骨架，首次描述了稀有瓦萨奇期鬣齿兽科类群Galecyon的颅后遗骸。Galecyon被复原为体重5.2~7.9千克的陆生食肉动物。其整体骨架存在细微却关键的差异，可将其与Prolimnocyon区分开来。Galecyon被复原为兼具攀援能力的广义陆生食肉动物，因为这些颅后骨骼的差异一致表明，其陆生习性比攀援型的Prolimnocyon更强。在其他鬣齿兽科类群中，Arfia展现出平行陆生适应的证据，而Pyrocyon的形态特征介于Galecyon与Prolimnocyon之间。通过对保存完好的Galecyon距跟关节（crurotarsal joint）骨骼进行操作分析，本研究获得的证据与此前的一项假说相悖——该假说认为另一种瓦萨奇期鬣齿兽科类群Arfia具备后足反转能力。在这两个属中，距跟关节的运动基本被限制在矢状平面内。基于全新颅后骨骼特征矩阵的系统发育分析，支持始新世早期鬣齿兽科的系统发育关系拓扑结构，该结果与基于牙齿形态得到的拓扑结构存在差异。整合两类数据后，结果在多数方面支持牙齿形态得到的拓扑结构，但牙齿与颅后骨骼数据间的冲突表明，即便采样密度相对较高，可靠的系统发育分辨率仍难以实现。 补充数据：本文的补充材料可通过www.tandfonline.com/UJVPC免费获取。 本文引用格式：Zack, S. P. 及 K. D. Rose. 2015. 《Galecyon的颅后骨骼：早期鬣齿兽科（哺乳纲，鬣齿兽目）形态与运动多样性的证据》. 脊椎动物古生物学杂志（Journal of Vertebrate Paleontology）. DOI: 10.1080/02724634.2014.1001492.