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

<div><p>ABSTRACT</p><p>Hyaenodontidae 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. </p><p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP</p><p>Citation 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.</p>