RESEARCH ARTICLE Craniodental and humeral morphology of a new species of Masrasector (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts Matthew R. Borths1*, Erik R. Seiffert2 a1111111111 a1111111111 1 Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio, United States of America, 2 Department of Integrative Anatomical Sciences, Keck School of Medicine, a1111111111 University of Southern California, Los Angeles, California, United States of America a1111111111 a1111111111 * [email protected] Abstract OPEN ACCESS Hyaenodonta is a diverse clade of carnivorous mammals that were part of terrestrial fau- Citation: Borths MR, Seiffert ER (2017) nas in the Paleogene of Eurasia and North America, but the oldest record for the group is Craniodental and humeral morphology of a new Afro-Arabian, making the record there vital for understanding the evolution of this wide- species of Masrasector (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of spread group. Previous studies show an ancient split between two major clades of hyae- Egypt and locomotor diversity in hyaenodonts. nodonts that converged in hypercarnivory: Hyainailourinae and Hyaenodontinae. These PLoS ONE 12(4): e0173527. https://doi.org/ clades are each supported by cranial characters. Phylogenetic analyses of hyaenodonts 10.1371/journal.pone.0173527 also support the monophyly of Teratodontinae, an Afro-Arabian clade of mesocarnivorous Editor: Xijun Ni, Institute of Vertebrate to hypercarnivorous hyaenodonts. Unfortunately, the cranial anatomy of teratodontines is Paleontology and Paleoanthropology Chinese Academy of Sciences, CHINA poorly known, and aligning the clade with other lineages has been difficult. Here, a new species of the phylogenetically controversial teratodontine Masrasector is described Received: November 4, 2016 from Locality 41 (latest Priabonian, late Eocene) from the Fayum Depression, Egypt. The Accepted: February 17, 2017 hypodigm includes the most complete remains of a Paleogene teratodontine, including Published: April 19, 2017 largely complete crania, multiple dentaries, and isolated humeri. Standard and ªtip-datingº Copyright: © 2017 Borths, Seiffert. This is an open Bayesian analyses of a character-taxon matrix that samples cranial, postcranial, and den- access article distributed under the terms of the tal characters support a monophyletic Masrasector within Teratodontinae, which is con- Creative Commons Attribution License, which sistently placed as a close sister group of Hyainailouridae. The cranial morphology of permits unrestricted use, distribution, and reproduction in any medium, provided the original Masrasector provides new support for an expanded Hyainailouroidea (Teratodontinae + author and source are credited. Hyainailouridae), particularly characters of the nuchal crest, palate, and basicranium. A Data Availability Statement: Data is available from discriminant function analysis was performed using measurements of the distal humerus MorphoSource with the identifier P191: from a diverse sample of extant carnivorans to infer the locomotor habits of Masrasector. Craniodental and humeral morphology of a new Masrasector was assigned to the ªterrestrialº locomotor category, a result consistent with à à species of Masrasector (Teratodontinae, the well-defined medial trochlear ridges, and moderately developed supinator crests of Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts. the specimens. Masrasector appears to have been a fast-moving terrestrial form with a diverse diet. These specimens considerably improve our understanding of Teratodonti- Funding: Field work in the Fayum Depression, Egypt, and digital curation of Fayum fossils is nae, an ancient member of the Afro-Arabian mammalian fauna, and our understanding of supported by the U.S. National Science Foundation PLOS ONE | https://doi.org/10.1371/journal.pone.0173527 April 19, 2017 1 / 60 Cranial and humeral material from Masrasector nananubis through grants BCS-0416164 (https://www.nsf. hyaenodont diversity before the dispersal of Carnivora to the continent near the end of the gov/awardsearch/showAward?AWD_ID= Paleogene. 0416164), BCS-0819186 (https://nsf.gov/ awardsearch/showAward?AWD_ID=0819186), and BCS-1231288 (https://www.nsf.gov/ awardsearch/showAward?AWD_ID=1231288), Gordon and Ann Getty, and The Leakey Foundation (https://leakeyfoundation.org/). MRB was supported by a U.S. National Science Foundation Introduction Doctoral Dissertation Improvement Grant (DEB- 1311354; https://www.nsf.gov/awardsearch/ The modern African terrestrial carnivore fauna is primarily composed of species from Carniv- showAward?AWD_ID= ora, but members of that order only appear in the Afro-Arabian fossil record during the latest 1311354&HistoricalAwards=false), a National Oligocene [1±2]. For most of the Paleogene in Afro-Arabia, terrestrial carnivorous niches were Science Foundation Graduate Research Fellowship occupied by Hyaenodonta, an extinct radiation of placental mammals whose members have (https://www.nsfgrfp.org/), a Turkana Basin also been found in Europe, Asia, and North America. Hyaenodonts were morphologically Institute Graduate Fellowship (http://www. diverse, ranging from the small, weasel-sized [3] to the wolf-sized turkanabasin.org/about/fellowships/), and a Stony Proviverra typica Hyaenodon Brook University Graduate Council Fellowship, and horridus [4], and even up to the rhinoceros-sized Megistotherium osteothlastes [5]. Coupled is currently supported by a U.S. National Science with their extensive range in body size is a diversity of cranial, postcranial, and dental adapta- Foundation Postdoctoral Fellowship in Biology tions that allowed hyaenodonts to exploit arboreal, mesocarnivorous niches to cursorial, (DBI-1612062; https://www.nsf.gov/awardsearch/ hypercarnivorous niches [6±8]. showAward?AWD_ID=1612062). Portions of the Unfortunately, the Paleogene Afro-Arabian radiation of hyaenodonts is still not well data acquisition for this study were also supported by grants from The Explorers Club (https:// understood. One reason for this may be that the fossil record of this group is dominated by explorers.org/expeditions/funding/expedition_ dental specimens; only five taxa (ªPterodonº africanus, Apterodon macrognathus, Megis- grants) and the Society for Integrative and totherium osteothlastes, and the recently published [9] Brychotherium ephalmos, and Comparative Biology (http://www.sicb.org/grants/ Akhnatenavus nefertiticyon) are known from substantial cranial material, and only a few fgstinfo.php). The funders had no role in study postcranial elements have been described [5, 10±11]. As such, we know little about the life- design, data collection and analysis, decision to styles of early Afro-Arabian hyaenodonts, aside from the inference that they all were, to publish, or preparation of the manuscript. some extent, carnivorous based on dental comparisons with modern Carnivora [12]. The Competing interests: The authors have declared Afro-Arabian record stands in contrast to the more complete record of hyaenodont remains that no competing interests exist. from Europe, North America, and Asia [3, 11±18]. The record from North America, in par- ticular, has provided our baseline understanding of early hyaenodont cranial and postcranial morphology [4, 6, 13, 16, 19, 20]. Teratodontinae, originally erected to contain the dentally bizarre early Miocene genus Tera- todon [21], which possesses massive, bunodont premolars, was first recognized as a clade by Sole et al. [22]. Teratodontinae is a clade of largely Afro-Arabian species, the early members of which appear to have been dietary generalists [9, 22]. In contrast, known Miocene species show great disparity in dental morphology and body size [8, 21, 27]. Borths et al. [9] found that the following teratodontines consistently form a clade to the exclusion of all other hyaeno- donts in a majority of the trees generated using parsimony and Bayesian methodsÐearly- middle Eocene Furodon and Glibzegdouia from Algeria [22]; late Eocene Brychotherium from Egypt [9]; early Oligocene Masrasector from northern Afro-Arabia [23±25]; early Miocene Teratodon from Egypt, Kenya, and Uganda [21, 26]; early Miocene Anasinopa from Kenya [21]; and middle-late Miocene Dissopsalis from Kenya and south Asia [27]. More broadly, these teratodontines were placed as a sister group of another largely Afro-Arabian clade, Hyai- nailouridae (Hyainailourinae + Apterodontinae) in a majority of parsimony- and Bayesian- derived consensus trees. Borths et al. [9] proposed that the clade that includes Teratodontinae, Hyainailourinae, and Apterodontinae be called Hyainailouroidea, and that name is used here. Hyainailouroidea may or may not include Eocene Asian ªindohyaenodontinesº (Indohyaeno- don, Paratritemnodon, and Kyawdawia) and early Oligocene African Metasinopa, as their positions differed in the analyses of Borths et al. [9] depending on the phylogenetic method employed. PLOS ONE | https://doi.org/10.1371/journal.pone.0173527 April 19, 2017 2 / 60 Cranial and humeral material from Masrasector nananubis Previously, the species that are now recognized as teratodontines were placed in various positions relative to other hyaenodonts, either as (1) part of a generalist group with European and Asian taxa [27], (2) part of an ªAfroasian proviverrineº clade whose interrelationships implied multiple dispersal