Bovidae

ABSTRACT The Kibish Formation of southern Ethiopia has yielded the earliest fossils of Homo sapiens, ca. 196 Ka, and has thus figured prominently in discussions of the origins of modern humans. Here we describe the fossil Bovidae from the Kibish Formation, a record that spans the late Middle Pleistocene to the early to mid-Holocene, and reconstruct aspects of their dietary ecology using mesowear analyses. All of the Kibish bovids represent extant taxa with the exception of the extinct blesbok-like alcelaphin Damaliscus hypsodon; extinct arid-adapted forms Syncerus antiquus and Megalotragus, common in other Late Quaternary sites, are notably absent. Mesowear of the Kibish bovids suggests that the Late Quaternary specimens were characterized by diets with considerably more abrasion-dominated wear relative to their extant conspecifics. Finally, the Kibish record provides supporting evidence for recent phylogeographic hypotheses by demonstrating significant range expansions of Aepyceros melampus, Connochaetes taurinus, Hippotragus equinus, and, to a lesser extent, Kobus kob in the late Middle Pleistocene through the early to mid-Holocene coincident with humid phases that punctuated dry spells of the Late Quaternary.

Mammal teeth have evolved morphologies that allow for the efficient mechanical processing of different foods, therefore increasing dietary energy uptake for maintenance of high metabolic demands. However, individuals masticate foods with biomechanical properties at odds with the optimal function of a given tooth morphology. Here, we investigate tooth form and function using two quantitative 3D methods at different scales on the same individuals of nine bovid species. Dental topometry quantifies the gross morphology, and therefore , reflects evolutionary adaptive patterns. Surface texture analysis infers mechanical occlusal events, which reflect the actual tooth function, and is free from the influence of morphology. We found that tough foods can be satisfactorily exploited by grazing species with enamel ridge morphologies not more complex than those found in intermediate feeders and browsers. Thus, the evolution of enamel complexity is likely determined by a balance between adaptation and constraints. Wider enamel ridges seem to be a common functional trait in bovids to compensate for severe wear from abrasive foods and/or chipping from hard foods. Our results demonstrate that supposedly essential functional adaptations in tooth morphology may not be required to process food efficiently. This emphasizes the large plasticity between Boptimal^ morphology and the potential function of the tooth, and underscores the need to appreciate (apparently) maladap-tive structures in mammalian evolution as nevertheless effective functioning units.

The extinct genus Leptobos belongs to the tribe Bovini, the group of large-sized bovids that today includes buffaloes, bison and cattle, among others. Leptobos is reported from several Eurasian localities from Spain to China, spanning biochronologically for most of the Villafranchian Mammal Age (i.e., from the upper Pliocene to most of the Early Pleistocene). Characters of the cranium, especially the horn cores (absent in females), have been normally used to describe different species of this genus. Nevertheless, problems related to possible intraspecific variability including sexual dimorphism, to low sample richness in various localities and to the difficulty of identifying diagnostic characters especially in the postcranial skeleton have hampered to clarify the systematics and phylogenetic relationships within the genus.
The type species L. falconeri is described on cranial remains from the Early Pleistocene Pinjor Stage of the upper Siwaliks (Pakistan) (Rütimeyer, 1877-1878). Leptobos brevicornis and L. crassus are known from China (Mead et al., 2014). Several species have been described in Early to Late Villafranchian localities of Europe. In their recent review, Masini et al. (2013) recognize two different groups or lineages. The first includes L. stenometopon, L. merlai and L. furtivus, the second L. etruscus and L. vallisarni. Leptobos stenometopon is a small and primitive form characterized by long and spiral-shaped horn cores and rather brachyodont teeth. It occurs at Dusino and Montopoli (Early and early Middle Villafranchian, respectively). Leptobos merlai is a large bovid reported in Italy by fragmentary remains from Upper Valdarno and Castel Viscardo, whereas is well known from the Middle Villafranchian locality of Saint Vallier, France. Leptobos furtivus is a poorly known species based on fragmentary material from Senèze, France (Duvernois & Guérin, 1989), which may occur in some Italian Late Villafranchian localities. Leptobos etruscus and L. vallisarni are morphologically similar and strictly related. The first species is very common in early Late Villafranchian mammal assemblages of central Italy (as well as in several European sites). The second occurs in the late Late Villafranchian (Tasso-Farneta Faunal Units) and is probably derived from L. etruscus.
Here we describe new Leptobos material from Umbria, which represents the best-preserved Italian sample of the L. merlai-furtivus lineage in the Italian peninsula. The sample from Pantalla (Perugia, Olivola-Tasso Faunal Units) includes a nearly complete female cranium, a juvenile right maxilla with deciduous premolars and permanent first molar and a distal left tibia. An additional male cranium with horn cores from an unknown locality near Perugia is also described. These new fossils allow confirming the occurrence of the L. merlai-furtivus lineage in Italy in the Middle-Late Villafranchian and offer the opportunity to better define the anatomy and variability of these forms. The validity of the species L. furtivus, mainly based on size-related characters, is questioned.