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20) Law CJ. 2020. Sex-specific ontogenetic patterns of cranial morphology, theoretical bite force, and underlying jaw musculature in fishers and American martens. Journal of Anatomy. doi.org/10.1111/joa.13231

Goal: to examine sex‐specific ontogenetic changes in cranial morphology, musculature, and theoretical bite force in the fisher (Pekania pennanti ) and American marten (Martes americana) 

Findings: Cranial shape development drives ontogenetic increases in relative bite force and jaw adductor muscle size by broadening the zygomatic arches and enlargement of the sagittal crest

Findings: In contrast, sexual dimorphism in cranial shape does not translate to dimorphism in either relative bite forces or jaw adductor muscle size

Conclusion: These results reveal that morphological variation can have different influences on bite performance depending on the level of intraspecific variation that is examined (i.e. ontogenetic versus sexual dimorphism)


19) Law CJ. 2019. Solitary meat-eaters: solitary, carnivorous carnivorans exhibit the highest degree of sexual size dimorphism. Scientific Reports. 9:15344. doi.org/10.1038/s41598-019-51943-x

Goal: Determine how social system (as a proxy for sexual selection) and diet (as a proxy for natural selection) influenced the evolution of SSD in terrestrial carnivorans

Findings: Territorial solitary and carnivorous carnivorans exhibited selection towards increased degree of male-biased sexual size dimorphism compared to other carnivorans with alternative social systems and diets

Findings: Most carnivoran families do not follow predictions of Rensch’s rule of increased male-biased sexual size dimorphism with increasing body size

Conclusion: Both sexual selection and niche divergence work simultaneously to reinforce or increase sexual size dimorphism in extant terrestrial carnivorans


18) Law CJ & Mehta RS. 2019. Dry versus wet and gross: Comparisons between the dry skull method and gross dissection-based modeling in bite force estimations. Journal of Morphology. 280:1706–1713. doi.org/10.1002/jmor.21061

Goal:  Test how accurately skeletomuscular traits estimated from the dry skull method predicts traits derived from dissection-based biomechanical modeling

Findings: The dry skull method overestimates PCSA of the masseter but underestimates PCSA of the temporalis

Findings: Sexual dimorphism in skull shape affects temporalis PCSA estimations; the dry skull method predicted female temporalis PCSA well but underestimates male temporalis PCSA

Conclusion: The dry skull method provides an underestimation of theoretical bite force over ontogeny, and the underlying anatomical components driving bite force may be misrepresented


17) Law CJ. 2019. Evolutionary shifts in extant mustelid (Mustelidae: Carnivora) cranial shape, body size, and body shape coincides with the Mid-Miocene Climate Transition. Biology Letters. 15:20190155. doi.org/10.1098/rsbl.2019.0155

Goal: examine the timing of evolutionary shifts in cranial shape, body size and body shape within extant mustelids (martens, otters, polecats and weasels) during the climatic and environmental changes of the Cenozoic

Findings: Extant mustelid subclades evolved more elongate body plans followed by concurrent shifts towards smaller body sizes and more robust crania during the Late Miocene

Findings: These cranial and body adaptations allowed mustelids to exploit new resources, which in turn facilitated significant increases in species richness

Conclusion: Future work incorporating the fossil record is needed to understand whether selection for smaller, more elongate bodies and stronger jaws occurred within crown-ward mustelids or if extinct ancestors already exhibited those characteristics


16) Law CJ, Slater GJ, & Mehta RS. 2018. Shared extremes by ectotherms and endotherms: Body elongation in mustelids is associated with small size and reduced limbs. Evolution. 73:735–749. doi.org/10.1111/evo.13702

Goal: Tested if mustelid subclades exhibited evolutionary shifts towards more elongate bodies compared to the remaining clade

Findings: Weasels are elongate! Specifically, mustelids exhibit an evolutionary transition toward more elongate bodies driven by the elongation of the head and various regions of the axial skeleton

Findings: The elongation of the body is associated with the evolutionary reduction of body size and a reduction in forelimb length but not hindlimb length

Conclusion: The relationship between body elongation and forelimb length has not previously been quantitatively established for mammals but is consistent with trends exhibited by ectothermic vertebrates and suggests a common pattern of trait covariance associated with body shape evolution


15) Law CJ, Duran E, Hung N, Richards E, Santillan I, & Mehta RS. 2018. Effects of diet on cranial morphology and biting ability in musteloid mammals. Journal of Evolutionary Biology. 31:1918-1931. doi.org/10.1111/jeb.13385 

Goal: examine relationships between cranial size and shape, estimated bite force, and dietary ecologies across Musteloidea

Findings: Cranial size but not cranial shape predicts estimated bite forces in musteloids; many-to-one mapping of form to function may explain this pattern as the cranium is complex, and a variety of morphological shape differences contribute to similar relative biting performance outcomes

Findings: Musteloids with different diets exhibit different cranial shapes; however, they have similar estimated bite forces suggesting that other feeding performance metrics and potentially nonfeeding traits are also important contributors to cranial evolution


14) Higgins BA, Law CJ, & Mehta RS. 2018. Eat whole and less often: ontogenetic shift reveals size specialization on kelp bass by the California moray eel, Gymnothorax mordax. Oecologia. 188:875–887. doi.org/10.1007/s00442-018-4260-x 

Findings: California morays are dietary specialists, feeding primarily on kelp bass despite not being the most commonly occurring fish species in the environment

Findings: California morays exhibit an ontogenetic shift for kelp bass where maximum prey size increases with moray size but smaller prey are dropped from the diet

Findings: Moray bite forces increased disproportionately with increasing head size, suggesting that larger morays can consume prey that exceed their head lengths; however, there was no significant relationship between prey size and moray bite force, indicating that prey size selection is not limited by moray bite force


13) Law CJ & Mehta RS. 2018. Carnivory maintains cranial dimorphism between males and females: Evidence for niche divergence in extant Musteloidea. Evolution. 72:1950–1961. doi.org/10.1111/evo.13514

Findings: Niche divergence rather than sexual selection maintains the evolution of sexual dimorphism in cranial size and bite force across Musteloidea

Findings: Hypercarnivorous musteloids exhibit the greatest degree of cranial size and bite force dimorphism; in contrast, neither dietary regime nor social system influenced the evolution of sexual dimorphism in cranial shape

Conclusion: These results demonstrate the importance of diet in reducing intraspecific competition for resources as an important mechanism that maintains the evolution of sexual dimorphism in extant musteloids.


12) Law CJ, Slater G, & Mehta RS. 2018. Lineage diversity and size disparity in Musteloidea: testing patterns of adaptive radiation using molecular and fossil-based methods. Systematic Biology. 67:127–144. doi.org/10.1093/sysbio/syx047

Findings: Musteloids do not exhibit an adaptive radiation as previously hypothesized; however, a subclade of “elongate” mustelids exhibit increased lineage carrying capacity and increased rates of body length evolution but not body mass evolution

Findings: Lack of correspondence in rates of body mass and length evolution suggest that phenotypic evolutionary rates under a single morphological metric may not capture the evolution of diversity in clades that exhibit elongate body shapes

Conclusion: These results suggest that body elongation led to the radiation of some musteloids


11) Jones K† & Law CJ†. 2018. Differentiation of craniomandibular morphology in two sympatric Peromyscus mice (Cricetidae: Rodentia). Mammal Research. 63:277–283. †Joint first authors doi.org/10.1007/s13364-018-0364-2 

Findings: Granivorous Pinyon mice (Peromyscus truei) exhibit skulls that facilitate relatively larger jaw adductor muscles compared to insectivorous California mice (Peromyscus californicus)

Findings: Pinyon mice also exhibit higher mechanical advantage of the masseter jaw muscle

Conclusion: These traits are consistent with the dietary differences exhibited by the two sympatric species


10) Law CJ. 2018. Mustela sibirica (Carnivora: Mustelidae). Mammalian Species. 50:109-118. doi.org/10.1093/mspecies/sey013

Literature review of the Siberian weasel


9) Kienle SS, Law CJ, Costa DP, Berta A, & Mehta RS. 2017. Revisiting the behavioural framework of feeding in predatory aquatic mammals. Proceedings of the Royal Society B. 284:20171035. doi.org/10.1098/rspb.2017.1035

An aquatic tetrapod feeding cycle with 5 stages—ingestion, intraoral transport, processing, water removal and swallowing—allows aquatic mammals to be examined in the same framework as other tetrapods and provides flexibility to accommodate behaviorally diverse lineages

Evolution of aquatic tetrapod feeding is not a progression of linear events and should be modeled as a tree-like process


8) Law CJ, Baliga VB, Tinker MT, & Mehta RS. 2017. Asynchrony in craniomandibular development and growth in Enhydra lutris nereis (Carnivora: Mustelidae): Are southern sea otters born to bite? Biological Journal of Linnean Society. 121:420-438 doi.org/10.1093/biolinnean/blw050

The majority of sea otter skull growth and development occurs during the pup stage; however, the skull does not fully mature until adulthood and therefore may constrain feeding on hard-shelled prey

Sexual dimorphism in adult skulls arose through differences in developmental and growth rates and duration

Male crania mature faster to presumably reach adult biting ability sooner, gaining a competitive advantage in obtaining food and in male–male agonistic interactions


7) Hung N & Law CJ. 2016. Lutra lutra (Carnivora: Mustelidae). Mammalian Species. 48:109–122. doi.org/10.1093/mspecies/sew011

Literature review of the Eurasian otter


6) Law CJ, Young C, and Mehta RS. 2016. Ontogenetic scaling of theoretical bite forces in southern sea otters (Enhydra lutris nereis). Physiological and Biochemical Zoology 89:347-363. doi.org/10.1086/688313

Sea otters exhibit positive allometric increases in theoretical bite force, which is primarily driven by allometric increases in temporalis muscle mass

Adult males exhibited greater bite forces as a result of their larger sizes

However, scaling patterns of theoretical bite force and morphological traits do not differ between the sexes


5) Law CJ, Venkatram V, & Mehta RS. 2016. Sexual dimorphism of craniomandibular morphology in southern sea otters (Enhydra lutris nereis). Journal of Mammalogy. 97:1764-1773. doi.org/10.1093/jmammal/gyw148

Male sea otters exhibit larger skulls compared to females

Sea otters also exhibit significant shape differences driven by 3 craniomandibular traits that increase the surface area of jaw muscle attachment sites

These morphological differences indicate males and females may also exhibit differences in biting abilities


4) Baliga VB & Law CJ. 2016. Cleaners amongst wrasses: phylogenetics and evolutionary patterns of cleaning behavior within Labridae. Molecular Phylogenetics and Evolution. 94A:424–435. doi.org/10.1016/j.ympev.2015.09.006


3) Law CJ, Dorgan KM, & Rouse GW. 2014. Relating divergence in polychaete musculature to different burrowing behaviors: A study using Opheliidae (Annelida). Journal of Morphology. 571:548–571. doi.org/10.1002/jmor.20237


2) Dorgan KM, Law CJ, & Rouse GW. 2013. Meandering worms: Mechanics of undulatory burrowing in muds. Proceedings of the Royal Society B. 280:20122948. doi.org/10.1098/rspb.2012.2948


1) Law CJ, Dorgan KM, & Rouse GW. 2013. Validation of three sympatric Thoracophelia species (Annelida: Opheliidae) from Dillon Beach, California using mitochondrial and nuclear DNA sequence data. Zootaxa. 3608:67–74. doi.org/10.11646/zootaxa.3608.1.4

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Department of Mammalogy & Division of Paleontology
American Museum of Natural History
200 Central Park West
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Email: claw@amnh.org