An official website of the United States government
Abstract ObjectivesCortical bone geometry is commonly used to investigate biomechanical properties of primate mandibles. However, the ontogeny of these properties is less understood. Here we investigate changes in cortical bone cross‐sectional properties throughout capuchin ontogeny and compare captive versus wild, semi‐provisioned groups. Tufted capuchins (Sapajusspp.) are known to consume relatively hard/tough foods, while untufted capuchins (Cebusspp.) exploit less mechanically challenging foods. Previous research indicates dietary differences are present early in development and adultSapajusmandibles can resist higher bending/shear/torsional loads. Materials and methodsThis study utilized microCT scans of 22Cebusand 45Sapajusfrom early infancy to adulthood from three sample populations: one captiveCebus, one captiveSapajus, and one semi‐provisioned, free‐rangingSapajus. Mandibular cross‐sectional properties were calculated at the symphysis, P3, and M1. If the tooth had not erupted, its position within the crypt was used. A series of one‐way ANOVAs were performed to assess differences between and within the sample populations. ResultsMandible robusticity increases across ontogeny for all three sample populations.Sapajuswere better able to withstand bending and torsional loading even early in ontogeny, but no difference in shear resistance was found. Semi‐provisioned, free‐rangingSapajustend to show increased abilities to resist bending and torsional loading but not shear loading compared to captiveSapajus. DiscussionThis study helps advance our understanding of the primate masticatory system development and opens the door for further studies into adaptive plasticity in shaping the masticatory apparatus of capuchins and differences in captive versus free‐ranging sample populations.
more »
« less
Bending performance changes during prolonged canine eruption in saber‐toothed carnivores: A case study of Smilodon fatalis
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
- Award ID(s):
- 2128146
- PAR ID:
- 10520474
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- The Anatomical Record
- ISSN:
- 1932-8486
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Systems of the body develop in a modular manner. For example, neural development in primates is generally rapid, whereas dental development varies much more. In the present study, we examined development of the skull, teeth, and postcrania in a highly specialized leaping primate,Galago moholi. Eighteen specimens ranging from birth to adult were studied. Bones, teeth, and the cranial cavity (i.e., endocast) were reconstructed with Amira software based on microCT cross‐referenced to histology. Amira was also used to compute endocast volume (as a proxy for brain size). Reconstructions of the wrist and ankle show that ossification is complete at 1 month postnatally, consistent with the onset of leaping locomotion in this species. Endocranial volume is less than 50% of adult volume at birth, ~80% by 1 month, and has reached adult volume by 2 months postnatal age. Full deciduous dentition eruption occurs by 2 weeks, and the young are known to begin capturing and consuming arthropods on their own by 4 weeks, contemporaneous with the timing of bone and ankle ossification that accompanies successful hunting. The modular pattern of development of body systems inGalago moholiprovides an interesting view of a “race” to adult morphology for some joints that are critical for specialized leaping and clinging, rapid crown mineralization to begin a transitional diet, but perhaps more prolonged reliance on nursing to support brain growth.more » « less
-
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.more » « less
-
ABSTRACT Rodent models have provided a detailed body of knowledge on craniodental development. Yet, it is unknown how well altricial mammals such as mice parallel primate and specifically human craniodental development. To address this, here we document the ontogeny of jaw‐related structures in a cross‐sectional prenatal sample of mouse lemurs (Microcebusspp.). Mouse lemurs follow the same developmental sequence as humans and mice with respect to the earliest appearance of jaw structures. Meckel's cartilage forms before any membranous bone of the mandibular body; mandibular basal bone begins to ossify before teeth enter the bud stage. Lower jaw structures commence morphogenesis before the corresponding maxillary elements. The basal bone of both jaws becomes more complex in larger fetuses. As tooth germs mature, the follicle—a supporting connective tissue outside the papilla and enamel organ—matures into a cellular, loosely fibrous tissue. Surrounding the follicle is a sheet‐like connective tissue, theepifollicular membrane. In tooth germs reaching the bell stage, alveolar bone forms within this membrane. One subtle distinction of mouse lemurs to prior descriptions of fetal anthropoids is the lemur's faster maturation of the deciduous canine compared to incisors, the reverse of the anthropoid pattern. However, broadly it appears that all primates studied thus far have a very prolonged duration of dental maturation, which continues long after other facial elements (e.g., hard palate) are fully formed. This scenario contrasts with altricial rodents, in which palate formation occurs near parturition, and only a day before the first permanent molar reaches the bell stage.more » « less
-
Abstract Thin-walled corrugated tubes that have a bending multistability, such as the bendy straw, allow for variable orientations over the tube length. Compared to the long history of corrugated tubes in practical applications, the mechanics of the bending stability and how it is affected by the cross sections and other geometric parameters remain unknown. To explore the geometry-driven bending stabilities, we used several tools, including a reduced-order simulation package, a simplified linkage model, and physical prototypes. We found the bending stability of a circular two-unit corrugated tube is dependent on the longitudinal geometry and the stiffness of the crease lines that connect separate frusta. Thinner shells, steeper cones, and weaker creases are required to achieve bending bi-stability. We then explored how the bending stability changes as the cross section becomes elongated or distorted with concavity. We found the bending bi-stability is favored by deep and convex cross sections, while wider cross sections with a large concavity remain mono-stable. The different geometries influence the amounts of stretching and bending energy associated with bending the tube. The stretching energy has a bi-stable profile and can allow for a stable bent configuration, but it is counteracted by the bending energy which increases monotonically. The findings from this work can enable informed design of corrugated tube systems with desired bending stability behavior.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/ar.25447
