Hard-Object Feeding in Sooty Mangabeys (Cercocebus atys) and Interpretation of Early Hominin Feeding Ecology

Abstract

Morphology of the dentofacial complex of early hominins has figured prominently in the inference of their dietary adaptations. Recent theoretical analysis of craniofacial morphology of Australopithecus africanus proposes that skull form in this taxon represents adaptation to feeding on large, hard objects. A modern analog for this specific dietary specialization is provided by the West African sooty mangabey, Cercocebus atys. This species habitually feeds on the large, exceptionally hard nuts of Sacoglottis gabonensis, stereotypically crushing the seed casings using their premolars and molars. This type of behavior has been inferred for A. africanus based on mathematical stress analysis and aspects of dental wear and morphology. While postcanine megadontia, premolar enlargement and thick molar enamel characterize both A. africanus and C. atys, these features are not universally associated with durophagy among living anthropoids. Occlusal microwear analysis reveals complex microwear textures in C. atys unlike those observed in A. africanus, but more closely resembling textures observed in Paranthropus robustus. Since sooty mangabeys process hard objects in a manner similar to that proposed for A. africanus, yet do so without the craniofacial buttressing characteristic of this hominin, it follows that derived features of the australopith skull are sufficient but not necessary for the consumption of large, hard objects. The adaptive significance of australopith craniofacial morphology may instead be related to the toughness, rather than the hardness, of ingested foods.

Experimental perspective on fallback foods and dietary adaptations in early hominins

“…The properties of foods eaten by species of Australopithecus are more difficult to infer, but differences between these hominins and Ar. ramidus in jaw robusticity, megadontia, and microwear [3,4], combined with the absence of a hard-object microwear signature [11], suggests tough-object feeding [26], but not to the degree inferred for P. boisei. We posit, therefore, that increases in jaw robusticity from Ardipithecus to Australopithecus to P. boisei reflect progressively greater reliance on tough, probably 13 C-enriched [27] foods and concomitantly elevated masticatory stresses owing to higher repetitive loading and longer load durations resulting from extended bouts of milling and grinding [11].…”

Isotopic evidence of early hominin diets

“…There exist clear priorities for morphological and microwear research. Additional work distinguishing the morphological (and microstructural) correlates of diets requiring repetitive vs. high-magnitude loading (7,8,69,70) is required, and effort should be focused on the types of foods that were potentially processed by flat australopith molars. For instance, is there anything about the rotatory movement of the Paranthropus mandible during chewing (77) that, when coupled with its occlusal morphology, enamel microstructure, and dental macrowear, allowed more effective processing of tough food items than previously thought possible?…”

Anterior dental microwear texture analysis of the Krapina Neandertals

“…While counts and measurements of microscopic scratches and pits have shown important associations between microwear pattern and diet/tooth use, three-dimensional characterizations of overall surface textures have become an increasingly popular alternative to feature-based microwear studies [26,29,38]. Dental microwear texture analysis combines white-light confocal profilometry and scale-sensitive fractal analysis, an engineering protocol rooted in fractal geometry [31].…”