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Abstract The evolution of complex dentitions in mammals was a major innovation that facilitated the expansion into new dietary niches, which imposed selection for tight form–function relationships. Teeth allow mammals to ingest and process food items by applying forces produced by a third-class lever system composed by the jaw adductors, the cranium, and the mandible. Physical laws determine changes in jaw adductor (biting) forces at different bite point locations along the mandible (outlever), thus, individual teeth are expected to experience different mechanical regimes during feeding. If the mammal dentition exhibits functional adaptations to mandible feeding biomechanics, then teeth are expected to have evolved to develop mechanically advantageous sizes, shapes, and positions. Here, we present bats as a model system to test this hypothesis and, more generally, for integrative studies of mammal dental diversity. We combine a field-collected dataset of bite forces along the tooth row with data on dental and mandible morphology across 30 bat species. We (1) describe, for the first time, bite force trends along the tooth row of bats; (2) use phylogenetic comparative methods to investigate relationships among bite force patterns, tooth, and mandible morphology; and (3) hypothesize how these biting mechanics patterns may relate to the developmental processes controlling tooth formation. We find that bite force variation along the tooth row is consistent with predictions from lever mechanics models, with most species having the greatest bite force at the first lower molar. The cross-sectional shape of the mandible body is strongly associated with the position of maximum bite force along the tooth row, likely reflecting mandibular adaptations to varying stress patterns among species. Further, dental dietary adaptations seem to be related to bite force variation along molariform teeth, with insectivorous species exhibiting greater bite force more anteriorly, narrower teeth and mandibles, and frugivores/omnivores showing greater bite force more posteriorly, wider teeth and mandibles. As these craniodental traits are linked through development, dietary specialization appears to have shaped intrinsic mechanisms controlling traits relevant to feeding performance.
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Sharpening our understanding of saber‐tooth biomechanics
Abstract Saber‐teeth are a striking example of convergent evolution in vertebrate predators, having evolved multiple times in mammals and their early ancestors. While there is broad consensus that saber‐toothed taxa employed a distinct biting strategy compared to conical‐toothed carnivores, like the lion, the precise mechanics and variability of this bite remain debated. In this review, we integrate current knowledge of pointed tooth mechanics and puncture mechanics to explore predatory function, focusing on the canine shear‐bite hypothesis. We quantify the key morphological characteristics of saber‐teeth–elongation, slenderness, curvature, sharpness, and cross‐sectional shape in a sample of saber‐and conical‐toothed taxa. Using the morphological diversity observed and insights from experimental studies, we examine the capacity of saber‐teeth to perform the canine shear‐bite, contrasting them with the clamp‐and‐hold bite of extant carnivores with conical canines. Our findings indicate that the morphological characteristics associated with extreme saber‐tooth forms, as seen inSmilodon, suggest the prioritization of deeper puncture and slicing actions and limiting of lateral loads, favorable for a canine shear‐bite. However, we also demonstrate that these morphological characteristics exist on a continuum accross saber‐toothed taxa suggesting greater functional diversity beyond the shear‐bite versus clamp‐and‐hold bite dichotomy. While this study refines our understanding of saber‐tooth function, key gaps remain, particularly regarding the role of cross‐sectional shape, curvature, and serrations in puncture mechanics.
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- Award ID(s):
- 1942906
- PAR ID:
- 10664104
- Publisher / Repository:
- American Association for Anatomy
- Date Published:
- Journal Name:
- The Anatomical Record
- Volume:
- 308
- Issue:
- 11
- ISSN:
- 1932-8486
- Page Range / eLocation ID:
- 3022 to 3040
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The canine of saber‐toothed predators represents one of the most specialized dental structures known. Hypotheses about the function of hypertrophied canines range from display and conspecific interaction, soft food processing, to active prey acquisition. Recent research on the ontogenetic timing of skull traits indicates the adult canine can take years to fully erupt, but the consequences of prolonged eruption on inferences of canine functional morphology are missing from current discourse and have not been quantified. Here I evaluate hypotheses about adult canine bending strength and stiffness, respectively, during eruption in the felidSmilodon fatalis. Simulated eruption sequences of three adult canines were generated from specimen models to assess shifting cross‐sectional geometry properties, and bending strength and stiffness under laterally directed loads were estimated using finite element analysis. Consistent with beam theory expectations,S. fataliscanine cross‐sectional geometry is optimized for increased bending strength with increased erupted height. However, canine cross‐sectional geometry changes through eruption exaggerate rather than minimize lateral deflection. Spatial constraint for maximum root length from adjacent sensory structures in the maxilla and the recently identified universal power law are hypothesized to limit the growth capacity of canine anteroposterior length and, consequently, maintenance of bending stiffness through eruption. Instead, the joint presence of the deciduous and adult canines for >50% of the adult canine eruption period effectively increases canine mediolateral width and brings bending strength and stiffness estimates closer to theoretical optima. Similarly prolonged retention of deciduous canines in other sabertooths suggests dual‐canine buttressing is a convergently evolved strategy to maximize bending strength and stiffness.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/ar.25690
