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 Borths,Erik R Seiffert

doi:10.1371/journal.pone.0173527

Matthew R Borths, Erik R Seiffert

Open Access

https://doi.org/10.1371/journal.pone.0173527

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Journal: PloS one	Publication Date: Apr 19, 2017
Citations: 20	License type: CC BY 4.0

Affiliation: Ohio University, University of Southern California

Abstract

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 Masrasector 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 Masrasector within Teratodontinae, which is consistently placed as a close sister group of Hyainailouridae. The cranial morphology of Masrasector 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 Masrasector. Masrasector 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. Masrasector 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.

Highlights

The modern African terrestrial carnivore fauna is primarily composed of species from Carnivora, but members of that order only appear in the Afro-Arabian fossil record during the latest Oligocene [1,2]
Within Chron C13r, Seiffert [34] argued that Locality 41 (L-41) was latest Priabonian in age based on the presence of a major unconformity above the fossil-bearing layer that might have been due to nearshore erosion associated with the major drop in sea level that occurred in the earliest Oligocene
Masrasector nananubis is a new species from the late Eocene locality of L-41 (Priabonian, ~34 Ma) in Egypt

Summary

Introduction

The modern African terrestrial carnivore fauna is primarily composed of species from Carnivora, but members of that order only appear in the Afro-Arabian fossil record during the latest Oligocene [1,2]. Hyaenodonts were morphologically diverse, ranging from the small, weasel-sized Proviverra typica [3] to the wolf-sized Hyaenodon horridus [4], and even up to the rhinoceros-sized Megistotherium osteothlastes [5] Coupled with their extensive range in body size is a diversity of cranial, postcranial, and dental adaptations that allowed hyaenodonts to exploit arboreal, mesocarnivorous niches to cursorial, hypercarnivorous niches [6,7,8]. The Paleogene Afro-Arabian radiation of hyaenodonts is still not well understood One reason for this may be that the fossil record of this group is dominated by dental specimens; only five taxa (“Pterodon” africanus, Apterodon macrognathus, Megistotherium osteothlastes, and the recently published [9] Brychotherium ephalmos, and Akhnatenavus nefertiticyon) are known from substantial cranial material, and only a few postcranial elements have been described [5, 10,11]. The record from North America, in particular, has provided our baseline understanding of early hyaenodont cranial and postcranial morphology [4, 6, 13, 16, 19, 20]

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