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Objectives: Archaeolemur is a recently extinct genus of lemur that is often compared to some Cercopithecidae, especially baboons. This is due in part to their derived dentition, with large anterior teeth and reduced bilophodont molars. Research involving comparative morphology, analysis of coprolites, isotopes, and enamel structure, have suggested Archaeolemur had an omnivorous diet involving mechanically challenging items. Yet, microwear analysis of posterior teeth does not necessarily support this conclusion. Materials and Methods: In this macroscopic study, dental chipping was recorded on permanent teeth of Archaeolemur from different localities (53 individuals; 447 permanent teeth; including both A. edwardsi and A. majori specimens). This study aimed to compare chipping patterns across the dentition of Archaeolemur with chipping in other primates. Results: The results show enamel chipping was prevalent on the anterior teeth of Archaeolemur (38.9% of anterior teeth showed at least one fracture) yet rare in posterior teeth (9%). There was a decrease in chipping frequency across the dentition, moving distally from incisors (50%; 20/40), through caniniform teeth (30%; 15/50), premolars (9.5%; 16/169), and molars (8.5%; 16/188). Discussion: The results support previous research suggesting Archaeolemur had a varied omnivorous diet in which the anterior dentition was used for extensive food processing. This likely included mechanically challenging items such as tough/hard large fruits, small vertebrates, and crustaceans. Such a high rate of chipping in the anterior dentition is uncommon in other primates, with exception of hominins. [ABSTRACT FROM AUTHOR]

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

The role of fallback foods in shaping primate ranging, socioecology, and morphology has recently become a topic of particular interest to biological anthropologists. Although the use of fallback resources has been noted in the ecological and primatological literature for a number of decades, few attempts have been made to define fallback foods or to explore the utility of this concept for primate evolutionary biologists and ecologists. As a preface to this special issue of the American Journal of Physical Anthropology devoted to the topic of fallback foods in primate ecology and evolution, we discuss the development and use of the fallback concept and highlight its importance in primatology and paleoanthropology. Am J Phys Anthropol 140:599-602, 2009. KEY WORDS diet; niche; keystone DOI 10.1002/ajpa.20978

What kinds of fractures do teeth sustain and how do they resist disintegration? This study involved the mechanical loading of extracted human and sea otter teeth using hard and soft indenters to simulate hard and soft diets. The tests were accompanied by real-time imaging. At least three types of fracture were seen in the enamel - median, radial and margin cracks. Each kind of fracture appears to have a different cause, although the distinction between median and radial cracks blurs as they propagate. Only margin cracks appear to form under soft indenters. Several aspects of tooth form can be described as devices to limit damage to a tooth crown against the onslaught of hard or soft foods. The damage modes of teeth are paralleled by the behavior of some bilayered hard foods. [ABSTRACT FROM AUTHOR]

Tooth enamel is brittle and highly susceptible to cracking. We propose that observations of such cracking can be used as a diagnostic tool for predicting bite force and inferring tooth function in living and fossil mammals. Laboratory tests on model tooth structures and extracted human teeth in simulated biting identify the principal fracture modes in enamel. Examination of museum specimens reveals the presence of similar fractures in a wide range of vertebrates, suggesting that cracks extended during ingestion or mastication. The use of fracture mechanics theory from materials engineering provides elegant relations for quantifying critical bite forces in terms of characteristic tooth size and enamel thickness. The role of enamel microstructure in determining how cracks initiate and propagate within the enamel (and beyond) is also explored. The picture emerges of teeth as damage tolerant structures, full of internal weaknesses and defects and yet able to contain the expansion of seemingly precarious cracks and fissures within the enamel shell. Such an understanding of 'dental fracture mechanics' can aid in the dietary reconstructions of extinct taxa. [ABSTRACT FROM AUTHOR]