Craniodental and humeral morphology of a new species of <i>Masrasector</i> (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts

<div><p>Hyaenodonta is a diverse clade of carnivorous mammals that were part of terrestrial faunas in the Paleogene of Eurasia and North America, but the oldest record for the group is Afro-Arabian, making the record there vital for understanding the evolution of this wide-spread group. Previous studies show an ancient split between two major clades of hyaenodonts that converged in hypercarnivory: Hyainailourinae and Hyaenodontinae. These clades are each supported by cranial characters. Phylogenetic analyses of hyaenodonts also support the monophyly of Teratodontinae, an Afro-Arabian clade of mesocarnivorous to hypercarnivorous hyaenodonts. Unfortunately, the cranial anatomy of teratodontines is poorly known, and aligning the clade with other lineages has been difficult. Here, a new species of the phylogenetically controversial teratodontine <i>Masrasector</i> is described from Locality 41 (latest Priabonian, late Eocene) from the Fayum Depression, Egypt. The hypodigm includes the most complete remains of a Paleogene teratodontine, including largely complete crania, multiple dentaries, and isolated humeri. Standard and “tip-dating” Bayesian analyses of a character-taxon matrix that samples cranial, postcranial, and dental characters support a monophyletic <i>Masrasector</i> within Teratodontinae, which is consistently placed as a close sister group of Hyainailouridae. The cranial morphology of <i>Masrasector</i> provides new support for an expanded Hyainailouroidea (Teratodontinae + Hyainailouridae), particularly characters of the nuchal crest, palate, and basicranium. A discriminant function analysis was performed using measurements of the distal humerus from a diverse sample of extant carnivorans to infer the locomotor habits of <i>Masrasector</i>. <i>Masrasector</i> was assigned to the “terrestrial” locomotor category, a result consistent with the well-defined medial trochlear ridges, and moderately developed supinator crests of the specimens. <i>Masrasector</i> appears to have been a fast-moving terrestrial form with a diverse diet. These specimens considerably improve our understanding of Teratodontinae, an ancient member of the Afro-Arabian mammalian fauna, and our understanding of hyaenodont diversity before the dispersal of Carnivora to the continent near the end of the Paleogene.</p></div

Tip-dating consensus tree.

<p>“Allcompat” (majority rule plus compatible groups) consensus derived from the post-burnin sample of trees recovered by tip-dating Bayesian analysis. T# corresponds to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173527#pone.0173527.s003" target="_blank">S3 Table</a> and the results and discussion section. Posterior probability (PP) shown in italics to the right or below relevant node. Divergence dates represent median divergence date for clades and taxa. The vertical line over each geological age range (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173527#pone.0173527.s002" target="_blank">S2 Table</a> for sources of age information) is the median estimated age for the taxon based on the tip-dating analysis. Branch colors correspond to legend for % change/Ma along branches. More rapidly changing branches include more red and more slowly changing branches include more blue. Most rapidly evolving lineages are near the base of Hyaenodonta. Continental area of origin for each taxon is shown by the shading the proposed age range: <b>black</b>, Afro-Arabia; <b>grey</b>, Europe; <b>checked</b>, Asia or India; <b>white</b>, North America. <b>Aq.</b>, Aquitanian; <b>Bart.</b>, Bartonian; <b>Burd.</b>, Burdigalian; <b>Dan.</b>, Danian; <b>La.</b>, Langhian; <b>Late K</b>, Late Cretaceous; <b>Maa.</b>, Maastrichtian; <b>Me.</b>, Messinian; <b>Pria.</b>, Priabonian; <b>Sel.</b>, Selanian; <b>Ser.</b>, Serravallian; <b>Tha.</b>, Thanetian; <b>Torto.</b>, Tortonian.</p

Cranium of <i>Masrasector nananubis</i> (DPC 11990).

<p>Cranium of <i>Masrasector nananubis</i> sp. nov. (DPC 11990 with P²–M³) in (<b>A)</b> dorsal view, rostrum points left, (<b>B)</b> ventral view, rostrum points left.</p

Confusion matrix.

<p>Confusion matrix.</p

Average measurements of the upper dentition of <i>Masrasector nananubis</i>.

<p>Average measurements of the upper dentition of <i>Masrasector nananubis</i>.</p

Dental nomenclature used in this study.

<p>Upper left M² and lower left M₃ of <i>Proviverra typica</i> (A–E) showing dental terminology and measurements used in this study. (<b>A</b>) <i>Proviverra typica</i> M² in occlusal and (<b>B)</b>, buccal views and M₃ in (<b>C)</b>, occlusal (<b>D)</b>, lingual, and (<b>E)</b>, buccal views. Measurements are indicated in italics. Modified from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0173527#pone.0173527.ref009" target="_blank">9</a>].</p

Comparative sample of extant carnivoran humeri.

<p>Comparative sample of extant carnivoran humeri.</p

Sketch and model of <i>Masrasector nananubis</i> cranium (DPC 12157).

<p>Sketch of cranium <i>Masrasector nananubis</i> sp. nov. (DPC 12157 with alveoli for P^{1, 2}, complete P³–M³) in (<b>A)</b> dorsal view, rostrum points left, (<b>B)</b> ventral view, rostrum points left, (<b>C)</b> left lateral view, rostrum points left, (<b>D)</b> right lateral view, rostrum points right. Dotted lines indicate uncertain sutures or root of sagittal crest. Digital model of cranium in (<b>E)</b> dorsal, (<b>F)</b> ventral, (<b>G)</b> left lateral, and (<b>H)</b> right lateral views. The digital model was generated in Avizo and is available on Morphosource. Abbreviations: <b>bsp</b>, basisphenoid; <b>eam</b>, external auditory meatus; <b>eoc</b>, external occipital crista; <b>exo</b>, exoccipital; <b>exprm</b>, exposed promontorium; <b>fmg</b>, foramen magnum; <b>fov</b>, foramen ovale; <b>hgf</b>, hypoglossal foramen; <b>juf</b>, jugular foramen?; <b>occ</b>, occipital condyle; <b>pcp</b>, paracondylar process; <b>pgf</b>, post glenoid foramen; <b>pgp</b>, postglenoid process; <b>prm</b>, promontorium; <b>smf</b>, stylomastoid foramen; <b>squ</b>, squamosal; <b>th</b>, tympanohyal.</p

Descriptive humeral measurements for L-41 cf. <i>Masrasector</i>.

<p>Descriptive humeral measurements for L-41 cf. <i>Masrasector</i>.</p

Hyaenodont locomotor categories.

<p>Hyaenodont locomotor categories.</p