Browsing by Subject "Mandible"

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Open Access
A diminutive Pliocene guenon from Kanapoi, West Turkana, Kenya.
(Journal of human evolution, 2019-10) Plavcan, J Michael; Ward, Carol V; Kay, Richard F; Manthi, Fredrick K
Although modern guenons are diverse and abundant in Africa, the fossil record of this group is surprisingly sparse. In 2012 the West Turkana Paleo Project team recovered two associated molar teeth of a small primate from the Pliocene site of Kanapoi, West Turkana, Kenya. The teeth are bilophodont and the third molar lacks a hypoconulid, which is diagnostic for Cercopithecini. The teeth are the same size as those of extant Miopithecus, which is thought to be a dwarfed guenon, as well as a partial mandible preserving two worn teeth, previously recovered from Koobi Fora, Kenya, which was also tentatively identified as a guenon possibly allied with Miopithecus. Tooth size and proportions, as well as analysis of relative cusp size and shearing crest development clearly separate the fossil from all known guenons. Based on the Kanapoi material, we erect a new genus and species, Nanopithecus browni gen. et sp. nov. The small size of the specimen suggests either that dwarfing occurred early in the lineage, or at least twice independently, depending on the relationship of the new species with extant Miopithecus. Further, the distinctive habitat and geographic separation from Miopithecus suggests that the origin of small body size is not uniquely linked to the current habitat of Miopithecus, and possibly that relatives of extant Miopithecus were much more widely distributed in the past. This in turn argues caution in using extant biogeography in models of the origins of at least some guenons.
Open Access
Are we looking for loads in all the right places? New research directions for studying the masticatory apparatus of New World monkeys.
(Anat Rec (Hoboken), 2011-12) Vinyard, CJ; Taylor, AB; Teaford, MF; Glander, KE; Ravosa, MJ; Rossie, JB; Ryan, TM; Williams, SH
New World monkeys display a wide range of masticatory apparatus morphologies related to their diverse diets and feeding strategies. While primatologists have completed many studies of the platyrrhine masticatory apparatus, particularly morphometric analyses, we collectively acknowledge key shortcomings in our understanding of the function and evolution of the platyrrhine feeding apparatus. Our goal in this contribution is to review several recent, and in most cases ongoing, efforts to address some of the deficits in our knowledge of how the platyrrhine skull is loaded during feeding. We specifically consider three broad research areas: (1) in vivo physiological studies documenting mandibular bone strains during feeding, (2) metric analyses assessing musculoskeletal functional morphology and performance, as well as (3) the initiation of a physiological ecology of feeding that measures in vivo masticatory mechanics in a natural environment. We draw several conclusions from these brief reviews. First, we need better documentation of in vivo strain patterns in the platyrrhine skull during feeding given their empirical role in developing adaptive hypotheses explaining masticatory apparatus form. Second, the greater accuracy of new technologies, such as CT scanning, will allow us to better describe the functional consequences of jaw form. Third, performance studies are generally lacking for platyrrhine jaws, muscles, and teeth and offer exciting avenues for linking form to feeding behavior and diet. Finally, attempts to bridge distinct research agendas, such as collecting in vivo physiological data during feeding in natural environments, present some of the greatest opportunities for novel insights into platyrrhine feeding biology.
Open Access
Kinetics and Energetics of Feeding Behaviors in Daubentonia madagascariensis
(2017) Toler, Maxx Camden
The primary aim of this thesis was to quantify the ways Daubentonia uses its specialized feeding apparatus during naturalistic feeding behaviors. This can be divided into two main objectives. The first objective was to better understand how these extreme specializations function in the extractive foraging niche of Daubentonia. The second objective was to use Daubentonia to test for previously unmeasured behavioral modifications of bite forces using the post-cranial musculature. To do this I carried out two experiments measuring the kinetics of wood gnawing and the energetics of feeding behaviors. The main results of these experiments were: 1) Daubentonia does not generate relatively high magnitude bite forces during wood gnawing compared to their maximal voluntary bite force, but wood gnawing is extremely energetically costly compared to other feeding behaviors. 2) Daubentonia recruits post-cranial musculature during wood gnawing, most frequently generating a neck-extending moment that increased the magnitude of bite forces on the mandibular incisor. 3) The energetic costs of feeding were positively correlated with the toughness of foods. 4) The rate of energetic costs (J/s) incurred during the processing and mastication of whole nuts is not significantly greater than the rate of costs to masticate small pieces of nut kernels, but the increased handling time increases the net cost per gram of food consumed (J/g). Taken together, these experiments inform the primary aim of this study. Daubentonia appears to possess a highly specialized toolkit for fracturing stress-limited foods. Their large jaw adducting musculature, rodent-like incisors, and relatively short mandible allow them to produce large bite pressures to rapidly fracture the shells of nuts. Furthermore, it was demonstrated that Daubentonia transfers some forces from the post-cranial musculature to its incisors during wood gnawing and that the energetic costs of this wood gnawing behavior approach what is expected for sustained locomotor costs. This work illuminates a new avenue for investigation in jaw biomechanics: the assistance and modification of bite forces using the post-cranial musculature.