- Alt Name:
- gray wolf
- Department of Mammalogy Natural History Museum of Los Angeles County
- Specimen ID:
- LACM 23010
- Additional Media:
This is a cranium model of Canis lupus, the gray wolf, built from a medical CT scan dataset. The model was used in biomechanical simulations using finite element analysis (FEA). Specimen loan courtesy of Jim Dines (NHMLA). CT scan courtesy of Michael McNitt-Gray (UCLA).
- Are Cranial Biomechanical Simulation Data Linked to Known Diets in Extant Taxa? A Method for Applying Diet-Biomechanics Linkage Models to Infer Feeding Capability of Extinct Species
- Tseng, Z. J., Flynn, J. J.
- PLoS ONE 10(4): e0124020. doi:10.1371/journal.pone.012402
Performance of the masticatory system directly influences feeding and survival, so adaptive hypotheses often are proposed to explain craniodental evolution via functional morphology changes. However, the prevalence of “many-to-one” association of cranial forms and functions in vertebrates suggests a complex interplay of ecological and evolutionary histories, resulting in redundant morphology-diet linkages. Here we examine the link between cranial biomechanical properties for taxa with different dietary preferences in crown clade Carnivora, the most diverse clade of carnivorous mammals. We test whether hypercarnivores and generalists can be distinguished based on cranial mechanical simulation models, and how such diet-biomechanics linkages relate to morphology. Comparative finite element and geometric morphometrics analyses document that predicted bite force is positively allometric relative to skull strain energy; this is achieved in part by increased stiffness in larger skull models and shape changes that resist deformation and displacement. Size-standardized strain energy levels do not reflect feeding preferences; instead, caniform models have higher strain energy than feliform models. This caniform-feliform split is reinforced by a sensitivity analysis using published models for six additional taxa. Nevertheless, combined bite force-strain energy curves distinguish hypercarnivorous versus generalist feeders. These findings indicate that the link between cranial biomechanical properties and carnivoran feeding preference can be clearly defined and characterized, despite phylogenetic and allometric effects. Application of this diet-biomechanics linkage model to an analysis of an extinct stem carnivoramorphan and an outgroup creodont species provides biomechanical evidence for the evolution of taxa into distinct hypercarnivorous and generalist feeding styles prior to the appearance of crown carnivoran clades with similar feeding preferences.
- Testing Adaptive Hypotheses of Convergence with Functional Landscapes: A Case Study of Bone-Cracking Hypercarnivores
- Tseng, Z.J.
- PLOS ONE 8(5): e65305
Morphological convergence is a well documented phenomenon in mammals, and adaptive explanations are commonly employed to infer similar functions for convergent characteristics. I present a study that adopts aspects of theoretical morphology and engineering optimization to test hypotheses about adaptive convergent evolution. Bone-cracking ecomorphologies in Carnivora were used as a case study. Previous research has shown that skull deepening and widening are major evolutionary patterns in convergent bone-cracking canids and hyaenids. A simple two-dimensional design space, with skull width-to-length and depth-to-length ratios as variables, was used to examine optimized shapes for two functional properties: mechanical advantage (MA) and strain energy (SE). Functionality of theoretical skull shapes was studied using finite element analysis (FEA) and visualized as functional landscapes. The distribution of actual skull shapes in the landscape showed a convergent trend of plesiomorphically low-MA and moderate-SE skulls evolving towards higher-MA and moderate-SE skulls; this is corroborated by FEA of 13 actual specimens. Nevertheless, regions exist in the landscape where high-MA and lower-SE shapes are not represented by existing species; their vacancy is observed even at higher taxonomic levels. Results highlight the interaction of biomechanical and non-biomechanical factors in constraining general skull dimensions to localized functional optima through evolution.
- Cranial function in a late Miocene Dinocrocuta gigantea (Mammalia: Carnivora) revealed by comparative finite element analysis
- Tseng, Z.J.
- Biological Journal of the Linnean Society 96(1):51-67
Carnivoran ecomorphologies evolved repeatedly during the Cenozoic. Whereas extreme forms (e.g. sabretoothed predators) probably represent similarities in ecology, other morphologies are more subtle with respect to the extent of their shared niche space. Finite element models of the skulls of Dinocrocuta gigantea, Canis lupus, and Crocuta crocuta were constructed to test the interpretation of D. gigantea as a bone cracker, an interpretation made on the basis of its large, conical premolars, and robust cranial morphology. Dinocrocuta gigantea is also of interest because it represents a lineage that has been placed in its own family, sister to Hyaenidae. Thus, functional similarity in craniodental performance could represent rapid convergence. The findings obtained indicate that the crania of D. gigantea and C. crocuta perform better in stress dissipation and distribution than that of C. lupus, regardless of P3 or P4 biting. In particular, the domed frontal region of the bone crackers received lower and more evenly distributed stress than C. lupus. Thus, the craniodental forms of the two bone-crackers are linked by functional advantage over that of C. lupus. Further examination of lineages such as borophagine canids could elucidate the extent of functional convergence of the bone-cracking ecomorph across diverse groups.
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Cranial function in a late Miocene Dinocrocuta gigantea (Mammalia: Carnivora) revealed by comparative finite element analysis