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1. Three‐dimensional anatomy of the anthropoid bony pelvis

   https://doi.org/10.1002/ajpa.23425  

   Ward, Carol V. ; Maddux, Scott D. ; Middleton, Emily R. ( February 2018 , American Journal of Physical Anthropology)

   Pelvic form is hypothesized to reflect locomotor adaptation in anthropoids. Most observed variation is found in the ilium, which traditionally is thought to reflect thoracic and shoulder morphology. This article examines the articulated bony pelvis of anthropoids in three dimensions (3D) to test hypothesized variation in pelvic anatomy related to overall torso form.

   Sixty landmarks were collected on articulated pelves from 240 anthropoid individuals. Landmark data were subjected to a Generalized Procrustes Analysis. Principal Components Analysis was used to identify trends among taxa. Linear metrics were extracted, and bivariate allometric analysis was used to compare intergroup differences and scaling trends of specific dimensions.

   The combination of 3D and bivariate allometric analysis demonstrates a complex pattern of locomotor/phylogenetic and allometric influences on pelvic morphology. Apes have relatively narrower dorsal interiliac spacing than do most monkeys, with relatively smaller spinal muscle attachment areas but only minimally wider ventral bi‐iliac breadths. Hylobatids and atelids have a relatively more cranial position of their sacra than do other taxa, and hylobatids and cercopithecids relatively more retroflexed ischia. Within groups, the three pelvic joints (lumbosacral, sacroiliac, and hip) become relatively closer together with increasing body size.

   A three‐dimensional consideration of the articulated pelvis in anthropoids reveals determinants of pelvic variation not previously appreciated by studies of isolated hipbones. This study provides no support for the hypothesis that the ape pelvis is mediolaterally broader than that of monkeys in relative terms, as would be expected if iliac shape is related to hypothesized differences in thoracic breadth and shoulder orientation. Instead, apes, especially great apes, have relatively narrow sacra and longer lower pelves, related to their shorter, stiffer lumbar spines and torsos. This difference, coupled with strong positive allometry of iliac breadth and negative allometry of key pelvic lengths, along with some variation in ischial morphology in certain taxa, explains much of the variation in pelvic form among anthropoid primates.

    

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2. Relative hindlimb length and hindlimb segmental proportions as indicators of locomotor category in primates, rodents, and tree shrews

   Yapuncich GS, Hegarty E ( March 2022 , American journal of biological anthropology)

   Leaping is an important locomotor behavior for arboreal taxa such as primates, providing means to cross discontinuous substrates, escape predation, and/or capture prey. Primates that leap frequently have relatively longer hindlimbs than those taxa that leap less often. However, it is unknown if this pattern holds across a broader phylogenetic sample that includes non-primate arboreal taxa and non-primate specialized leapers. Here, we examine if relative hindlimb length and segmental proportions correlate with locomotor category across a sample of small-bodied (800g) mammals. Lengths of six hindlimb elements (summing to total hindlimb length) were measured on micro-computed tomography scans. Total hindlimb length was regressed against body mass to calculate relative hindlimb length. Segmental proportions were calculated as the ratio of femoral, tibial, and pedal (the sum of calcaneal, cuboidal, metatarsal, and phalangeal lengths) lengths to total hindlimb length. We found that while three arboreal/scansorial taxa (common marmosets, greater dwarf lemurs, and palm squirrels) exhibit short hindlimbs relative to their body mass, all other arboreal and scansorial taxa have relatively long hindlimbs. Most arboreal, scansorial, terrestrial, and fossorial taxa distribute length evenly across segments (femur, tibia, and pes each comprise 33% of total hindlimb length). Saltatorialists (e.g., jerboas and kangaroo rats) were the only locomotor group with exceptional proportions, with pedal segments contributing 38% of total hindlimb length. These results suggest to us that segmental proportions may distinguish specialized ricochetal hoppers from taxa that leap sporadically, while relative hindlimb length may predict general leaping ability across mammals. 

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3. Interspecific Variation of Calcaneal Morphology in Gorillas

   Harper, Christine M. ; Ruff, Christopher B. ; Sylvester, Adam D. ( February 2019 , American journal of physical anthropology)

   The foot plays a prominent role in weight-bearing suggesting it may reflect locomotor variation. Despite the immense amount of foot research, the calcaneus has been relatively understudied. Here we analyzed the entire calcaneal shape of Gorilla gorilla gorilla (n=41), Gorilla beringei graueri (n=17) and Gorilla beringei beringei (n=8) to understand how morphology relates to locomotor behavior. Calcanei were surface scanned and external shape analyzed using a three-dimensional geometric morphometric sliding semilandmark analysis. Semilandmarks were slid to minimize the bending energy of the thin plate spline interpolation function relative to the updated Procrustes average. Generalized Procrustes Analysis was used to align landmark configurations and shape variation was summarized using a principal components analysis. Procrustes distances between species were calculated and resampling statistics were run to test for group differences. All subspecies demonstrate statistically different morphologies (p<0.005 for pairwise comparisons). G. b. graueri separates from other subspecies based on posterolateral morphology, with G. b. graueri demonstrating an elongated peroneal trochlea, and thus more bone superiorly than G. g. gorilla. Compared to G. b. beringei, G. b. graueri has less bone inferiorly near the tuberosity. Cuboid and posterior talar facet shapes correlate with arboreality. G. b. beringei (most terrestrial) has a flatter cuboid facet and a more transversely oriented/relatively smaller posterior talar facet than G. g. gorilla (most arboreal) and G. b. graueri represents an intermediate morphology. These differences demonstrate a relationship between calcaneal shape and locomotor behavior and suggest that G. b. graueri may load its foot differently from the other subspecies. This project was supported by NSF grant # BCS - 1824630. 

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4. Footloose: Articular surface morphology and joint movement potential in the ankles of lorisids and cheirogaleids

   https://doi.org/10.1002/ajpa.24298  

   Yapuncich, Gabriel S. ; Granatosky, Michael C. ( April 2021 , American Journal of Physical Anthropology)

   The competing functional demands of diarthrodial joints, permitting mobility while retaining enough stability to transmit forces across the joint, have been linked with the shape and size of the joint's articular surfaces. A clear understanding of the relationship between joint morphology and joint movement potential is important for reconstructing locomotor behaviors in fossil taxa.

   In a sample of matched tali and calcanei of lorisids (n = 28) and cheirogaleids (n = 38), we quantify the surface areas of the talar and calcaneal ectal (=posterior talocalcaneal) articular surfaces and model the principal curvatures of these surfaces with quadric formulas. These two taxonomic groups have similar body masses, but differ substantially in positional behavior, so that differences in joint surface morphology should reflect adaptive demands of their locomotor behavior.

   Compared with cheirogaleids, lorisids exhibit: (a) a significantly greater area difference between their paired joint surfaces; and (b) a more pronounced saddle shape for the talar ectal facet.

   The increased subtalar joint mobility observed in lorisids may be achieved by increasing the amount of sliding and rolling that can occur at the subtalar joint. The subtalar joint morphology observed in two fossil euarchontans, the plesiadapiformsPurgatoriussp. andPlesiadapis cookei, compares favorably with the morphology observed among lorisids, potentially suggesting antipronograde postures within these extinct taxa.

    

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5. Ecomorphological correlates of inner and middle ear anatomy within phyllostomid bats

   https://doi.org/10.1002/ar.25178  

   Dickinson, Edwin ; Tomblin, Emily ; Rose, Madison ; Tate, Zoe ; Gottimukkula, Mihika ; Granatosky, Michael C. ; Santana, Sharlene E. ; Hartstone‐Rose, Adam ( February 2023 , The Anatomical Record)

   Echolocation is the primary sense used by most bats to navigate their environment. However, the influence of echolocating behaviors upon the morphology of the auditory apparatus remains largely uninvestigated. While it is known that middle ear ossicle size scales positively with body mass across mammals, and that peak call frequency scales negatively with body mass among bats, there are still large gaps in our understanding of the degree to which allometry or ecology influences the morphology of the chiropteran auditory apparatus. To investigate this, we used μCT datasets to quantify three morphological components of the inner and middle ear: ossicle size, ossicle shape, and cochlear spirality. These data were collected across 27 phyllostomid species, spanning a broad range of body sizes, habitats, and dietary categories, and the relationships between these variables and ear morphology were assessed using a comparative phylogenetic approach. Ossicle size consistently scaled with strong negative allometry relative to body mass. Cochlear spirality was significantly (p = .025) associated with wing aspect ratio (a proxy for habitat use) but was not associated with body mass. From a morphological perspective, the malleus and incus exhibited some variation in kind with diet and call frequency, while stapes morphology is more closely tied to body size. Future work will assess these relationships within other chiropteran lineages, and investigate potential morphological differences in the middle and inner ear of echolocating‐vs‐non‐echolocating taxa.

    

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