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A number of living primates feed part-year on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods--nuts, seeds, and root vegetables--were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads. Am J Phys Anthropol 140:643-652, 2009. KEY WORDS hardness; elastic modulus; fallback foods; fracture mechanics; bite force DOI 10.1002/ajpa.21026

Lucas and colleagues recently proposed a model based on fracture and deformation concepts to describe how mammalian tooth enamel may be adapted to the mechanical demands of diet (Lucas et al.: Bioessays 30[2008] 374-385). Here we review the applicability of that model by examining existing data on the food mechanical properties and enamel morphology of great apes (Pan, Pongo, and Gorilla). Particular attention is paid to whether the consumption of fallback foods is likely to play a key role in influencing great ape enamel morphology. Our results suggest that this is indeed the case. We also consider the implications of this conclusion on the evolution of the dentition of extinct hominins. Am J Phys Anthropol 140:653-660, 2009. KEY WORDS fracture mechanics; diet; evolution DOI 10.1002/ajpa.21096

Tooth enamel is inherently weak, with fracture toughness comparable with glass, yet it is remarkably resilient, surviving millions of functional contacts over a lifetime. We propose a microstructural mechanism of damage resistance, based on observations from ex situ loading of human and sea otter molars (teeth with strikingly similar structural features). Section views of the enamel implicate tufts, hypomineralized crack-like defects at the enamel--dentin junction, as primary fracture sources. We report a stabilization in the evolution of these defects, by 'stress shielding' from neighbors, by inhibition of ensuing crack extension from prism interweaving (decussation), and by self-healing. These factors, coupled with the capacity of the tooth configuration to limit the generation of tensile stresses in largely compressive biting, explain how teeth may absorb considerable damage over time without catastrophic failure, an outcome with strong implications concerning the adaptation of animal species to diet. dental enamel | evolutionary biology | fracture | microstructure | tufts

The African Plio--Pleistocene hominins known as australopiths evolved a distinctive craniofacial morphology that traditionally has been viewed as a dietary adaptation for feeding on either small, hard objects or on large volumes of food. A historically influential interpretation of this morphology hypothesizes that loads applied to the premolars during feeding had a profound influence on the evolution of australopith craniofacial form. Here, we test this hypothesis using finite element analysis in conjunction with comparative, imaging, and experimental methods. We find that the facial skeleton of the Australopithecus type species, A. africanus, is well suited to withstand premolar loads. However, we suggest that the mastication of either small objects or large volumes of food is unlikely to fully explain the evolution of facial form in this species. Rather, key aspects of australopith craniofacial morphology are more likely to be related to the ingestion and initial preparation of large, mechanically protected food objects like large nuts and seeds. These foods may have broadened the diet of these hominins, possibly by being critical resources that australopiths relied on during periods when their preferred dietary items were in short supply. Our analysis reconciles apparent discrepancies between dietary reconstructions based on biomechanics, tooth morphology, and dental microwear. evolution | face | finite element analysis | hominin | diet

The hypothesis that since furgivory by sympatric species of platyrrhines have unto six different color vision phenotypes, they might be expected to include fruits with a wide variety of hues in their diet is tested. The results suggest that most fruit species included in the diet can be discriminated by most color vision phenotype present in the population.

Author(s): Nathaniel J. Dominy (corresponding author); Peter W. Lucas Trichromatic colour vision, characterized by three retinal photopigments tuned to peak wavelengths of [similar]430 nm, [similar]535 nm and [similar]562 nm (refs [...]

Orang-utans (Pongo pygmaeus) at the Singapore Zoological Gardens were presented with two thick-shelled edible seeds, Mezzettia parviflora (Annonaceae) and Macadamia ternifolia (Proteaceae) in order to estimate their maximum bite forces. The orang-utans could break the Macadamia seeds in one bite, while those of Mezzettia required repeated attempts. Examination of shell fragments showed that many had scratches and some had clear, but small (ca. 1-2 mm diameter), impressions on them. Building upon this information, semi-imitative tests were performed on the seeds in a universal testing machine by loading them in compression with either flat plates or metal casts of orang-utan cheek teeth. The maximum forces required to break the seeds were similar with both the flat plates and the metal teeth; the average for the Macadamia seeds being about 2,000 N (which forms a minimum estimate for the maximum bite forces in orang-utans) and for the Mezzettia seeds, 6,000 N. The work done with the metal teeth was much greater than with the plates. A mechanical analysis showed that this extra work went into producing permanent impressions ('bite marks') in the shell with the tooth cusps. These impressions were larger than those found on the shells of seeds bitten by the orang-utans. Nevertheless, it is shown theoretically that the size of these indentations can give an estimate of the bite forces used. The maximum force developed in the machine tests with the metal teeth was correlated with the force calculated from analysis of the bite marks. The method is suitable for use in field studies where the marks left on remnants of hard foods eaten by primates may be used to estimate, very roughly, the forces used to produce them.

Evolution of the red-green visual subsystem in trichromatic primates is linked to foraging advantages, namely the detection of either ripe fruits or young leaves amid mature foliage. Competing hypotheses was tested globally for eight primate taxa: five with routine trichromatic vision and three without it.

Young leaves on many rain forest trees are red possibly due to invertebrate herbivores lacking a red vision receptor. Herbivore density generally relates to the quantity of edible foliage, in turn suggesting crypsis, or lack of visibility to herbivores, is the most probable reason for red leaf incidence.