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1. Long bone diaphyseal shape follows different ontogenetic trajectories in captive and wild gorillas

   https://doi.org/10.1002/ajpa.23636  

   Canington, Stephanie L. ; Sylvester, Adam D. ; Burgess, M. Loring ; Junno, Juho‐Antti ; Ruff, Christopher B. ( August 2018 , American Journal of Physical Anthropology)

   A number of studies have demonstrated the ontogenetic plasticity of long bone diaphyseal structure in response to mechanical loading. Captivity should affect mechanical loading of the limbs, but whether captive apes grow differently than wild apes has been debated. Here, we compare captive and wild juvenile and adultGorillato ascertain whether growth trajectories in cross‐sectional diaphyseal shape are similar in the two environments.

   A sample of young juvenile (n = 4) and adult (n = 10) captiveGorilla gorillagorillaspecimens, with known life histories, were compared with age‐matched wildG.g. gorilla(n = 62) andG. beringei beringei(n = 75) in relative anteroposterior to mediolateral bending strength of the femur, tibia, and humerus. Cross sections were obtained using peripheral quantitative CT.

   Captive and wild adultG.g. gorilladiffered in bending strength ratios for all three bones, but these differences were not present in young juvenileG.g. gorilla. In comparisons across taxa, captive juvenileG.g. gorillawere more similar to wildG.g. gorillathan toG.b. beringei, while captive adultG.g. gorillawere more similar in shape toG.b. beringeiin the hind limb.

   Captive and wildG. gorillafollow different ontogenetic trajectories in long bone diaphyseal shape, corresponding to environmental differences and subsequent modified locomotor behaviors. Differences related to phylogeny are most evident early in development.

    

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2. Ontogeny of cranial musculoskeletal anatomy and its relationship to allometric increase in bite force in an insectivorous bat ( Eptesicus fuscus )

   https://doi.org/10.1002/ar.25213  

   Stanchak, Kathryn E. ; Faure, Paul A. ; Santana, Sharlene E. ( April 2023 , The Anatomical Record)

   Bite force is a performance metric commonly used to link cranial morphology with dietary ecology, as the strength of forces produced by the feeding apparatus largely constrains the foods an individual can consume. At a macroevolutionary scale, there is evidence that evolutionary changes in the anatomical elements involved in producing bite force have contributed to dietary diversification in mammals. Much less is known about how these elements change over postnatal ontogeny. Mammalian diets drastically shift over ontogeny—from drinking mother's milk to feeding on adult foods—presumably with equally drastic changes in the morphology of the feeding apparatus and bite performance. Here, we investigate ontogenetic morphological changes in the insectivorous big brown bat (Eptesicus fuscus), which has an extreme, positive allometric increase in bite force during development. Using contrast‐enhanced micro‐computed tomography scans of a developmental series from birth to adult morphology, we quantified skull shape and measured skeletal and muscular parameters directly related to bite force production. We found pronounced changes in the skull over ontogeny, including a large increase in the volume of the temporalis and masseter muscles, and an expansion of the skull dome and sagittal crest that would serve to increase the temporalis attachment area. These changes indicate that development of the jaw adductors play an important role in the development of biting performance of these bats. Notably, static bite force increases with positive allometry with respect to all anatomical measures examined, suggesting that modifications in biting dynamics and/or improved motor coordination also contribute to increases in biting performance.

    

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3. Cranial joint histology in the mallard duck ( Anas platyrhynchos ): new insights on avian cranial kinesis

   https://doi.org/10.1111/joa.12562  

   Bailleul, Alida M. ; Witmer, Lawrence M. ; Holliday, Casey M. ( December 2016 , Journal of Anatomy)

   The evolution of avian cranial kinesis is a phenomenon in part responsible for the remarkable diversity of avian feeding adaptations observable today. Although osteological, developmental and behavioral features of the feeding system are frequently studied, comparatively little is known about cranial joint skeletal tissue composition and morphology from a microscopic perspective. These data are key to understanding the developmental, biomechanical and evolutionary underpinnings of kinesis. Therefore, here we investigated joint microstructure in juvenile and adult mallard ducks (Anas platyrhynchos; Anseriformes). Ducks belong to a diverse clade of galloanseriform birds, have derived adaptations for herbivory and kinesis, and are model organisms in developmental biology. Thus, new insights into their cranial functional morphology will refine our understanding of avian cranial evolution. A total of five specimens (two ducklings and three adults) were histologically sampled, and two additional specimens (a duckling and an adult) were subjected to micro‐computed tomographic scanning. Five intracranial joints were sampled: the jaw joint (quadrate‐articular); otic joint (quadrate‐squamosal); palatobasal joint (parasphenoid‐pterygoid); the mandibular symphysis (dentary‐dentary); and the craniofacial hinge (a complex flexion zone involving four different pairs of skeletal elements). In both the ducklings and adults, the jaw, otic and palatobasal joints are all synovial, with a synovial cavity and articular cartilage on each surface (i.e. bichondral joints) ensheathed in a fibrous capsule. The craniofacial hinge begins as an ensemble of patent sutures in the duckling, but in the adult it becomes more complex: laterally it is synovial; whereas medially, it is synostosed by a bridge of chondroid bone. We hypothesize that it is chondroid bone that provides some of the flexible properties of this joint. The heavily innervated mandibular symphysis is already fused in the ducklings and remains as such in the adult. The results of this study will serve as reference for documenting avian cranial kinesis from a microanatomical perspective. The formation of: (i) secondary articular cartilage on the membrane bones of extant birds; and (ii) their unique ability to form movable synovial joints within two or more membrane bones (i.e. within their dermatocranium) might have played a role in the origin and evolution of modern avian cranial kinesis during dinosaur evolution.

    

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4. An Older and Exceptionally Large Adult Specimen of Tyrannosaurus rex

   https://doi.org/10.1002/ar.24118  

   Persons, IV, W. Scott ; Currie, Philip J. ; Erickson, Gregory M. ( April 2019 , The Anatomical Record)

   Here we describe an extremely large and relatively complete (roughly 65%) skeleton ofTyrannosaurus rex(RSM P2523.8). Multiple measurements (including those of the skull, hip, and limbs) show that RSM P2523.8 was a robust individual with an estimated body mass exceeding all other knownT. rexspecimens and representatives of all other gigantic terrestrial theropods. Histological sampling of the fibula confirms that RSM P2523.8 is skeletally mature. The prevalence of incompletely coossified elements contradicts previous assertions that such unfused elements can be taken as indicators of somatic immaturity. As an extreme example of both ontogenetic maturity and osteological robustness, RSM P2523.8 offers support for prior hypotheses that a sampling bias occurs throughout the Dinosauria, making it likely that most taxa grew to significantly greater size than current known specimens indicate. Anat Rec, 303:656–672, 2020. © 2019 Wiley Periodicals, Inc.

    

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5. A chomped chimp: New evidence of tooth marks on an adult chimpanzee ( Pan troglodytes verus )

   https://doi.org/10.1002/ajpa.24049  

   Eller, Andrea R. ; Pobiner, Briana ; Friend, Sadie ; Austin, Rita M. ; Hofman, Courtney A. ; Sholts, Sabrina B. ( March 2020 , American Journal of Physical Anthropology)

   To describe and interpret previously unreported marks on the dry cranium of an adult chimpanzee (Pan troglodytesverus) from Côte d'Ivoire at the Smithsonian's National Museum of Natural History (USNM 450071).

   All marks on the cranium were documented and assessed through physical examination of the specimen, photography, micro‐computed tomography (micro‐CT), and 3D laser scanning. Pits and punctures were measured with digital calipers for comparison with published carnivore tooth mark measurements.

   The cranium shows perimortem or postmortem damage to the temporal, occipital, and maxillary regions that is not recent. Size and color variation in the marks suggest two damage events, possibly involving chewing by different animals, at least one of which was a large‐bodied mammal. The 22 tooth pits and punctures (0.89–8.75 mm in maximum length and 0.88–6.63 mm in breadth) overlap in size with those inflicted by wild leopards, the most significant predators of common chimpanzees due to their largely overlapping ecological distributions.

   Based on qualitative and quantitative evidence, we conclude that leopards are the most likely cause of the most prominent marks on the cranium. However, we cannot rule out the additional possibility of other chimpanzees, although there are no published studies of chimpanzee tooth marks for direct comparison. This study is the most extensive documentation to date of a modern adult chimpanzee skull exhibiting tooth marks by a large mammal, thus providing new evidence to help identify and interpret other events of predation and scavenging of large‐bodied apes in the modern and fossil records.

    

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