Synopsis Body size and body-size shifts broadly impact life-history parameters of all animals, which has made accurate body-size estimates for extinct taxa an important component of understanding their paleobiology. Among extinct crocodylians and their precursors (e.g., suchians), several methods have been developed to predict body size from suites of hard-tissue proxies. Nevertheless, many have limited applications due to the disparity of some major suchian groups and biases in the fossil record. Here, we test the utility of head width (HW) as a broadly applicable body-size estimator in living and fossil suchians. We use a dataset of sexually mature male and female individuals (n = 76) from a comprehensive sample of extant suchian species encompassing nearly all known taxa (n = 22) to develop a Bayesian phylogenetic model for predicting three conventional metrics for size: body mass, snout–vent length, and total length. We then use the model to estimate size parameters for a select series of extinct suchians with known phylogenetic affinity (Montsechosuchus, Diplocynodon, and Sarcosuchus). We then compare our results to sizes reported in the literature to exemplify the utility of our approach for a broad array of fossil suchians. Our results show that HW is highly correlated with all other metrics (all R2≥0.85) and is commensurate with femoral dimensions for its reliably as a body-size predictor. We provide the R code in order to enable other researchers to employ the model in their own research.
Carnivorans possess relatively large brains compared to most other mammalian clades. Factors like environmental complexity (Cognitive Buffer Hypothesis) and diet quality (Expensive-Tissue Hypothesis) have been proposed as mechanisms for encephalization in other large-brained clades. We examine whether the Cognitive Buffer and Expensive-Tissue Hypotheses account for brain size variation within Carnivora. Under these hypotheses, we predict a positive correlation between brain size and environmental complexity or protein consumption. Relative endocranial volume (PGLS residual from species mean body mass) and nine environmental and dietary variables were collected from the literature for 148 species of terrestrial and marine carnivorans. We found that the correlation between relative brain volume and environment and diet differed among clades, a trend consistent with other larger brained vertebrates (i.e., Primates, Aves). Mustelidae and Procyonidae demonstrate larger brains in species with higher quality diets, consistent with the Expensive-Tissue Hypothesis, while in Herpestidae correlations between relative brain size and environment are consistent with the Cognitive Buffer Hypothesis. Our results indicate that carnivorans may have evolved relatively larger brains under similar selective pressures as primates despite the considerable differences in life history and behavior between these two clades.
Pleistocene glacial cycles are thought to have driven ecological niche shifts, including novel niche formation. North American pine martens, Martes americana and M. caurina, are exemplar taxa thought to have diverged molecularly and morphologically during Pleistocene glaciation. Previous research found correlations between Martes limb morphology with biome and climate, suggesting that appendicular evolution may have occurred via adaptation to selective pressures imposed by novel and shifting habitats. Such variation can also be achieved through non-adaptive means such as genetic drift. Here, we evaluate whether regional genetic differences reflect limb morphology differences among populations of M. americana and M. caurina by analyzing evolutionary tempo and mode of six limb elements. Our comparative phylogenetic models indicate that genetic structure predicts limb shape better than size. Marten limb size has low phylogenetic signal, and the best supported model of evolution is punctuational (kappa), with morphological and genetic divergence occurring simultaneously. Disparity through time analysis suggests that the tempo of limb evolution in Martes tracks Pleistocene glacial cycles, such that limb size may be responding to shifting climates rather than population genetic structure. Contrarily, we find that limb shape is strongly tied to genetic relationships, with high phylogenetic signal and a lambda mode of evolution. Overall, this pattern of limb size and shape variation may be the result of geographic isolation during Pleistocene glacial advance, while declines in disparity suggest hybridization during interglacial periods. Future inclusion of extinct populations of Martes, which were more morphologically and ecologically diverse, may further clarify Martes phenotypic evolution. K E Y W O R D S limb shape, limb size, mustelid, phylogenetic comparative methods | INTRODUCTIONClimate is one of the most prominent extrinsic selective pressures influencing phenotypic evolution, as it often leads to shifts in environment that require adaptation or Evolution of Martes limb shape and size.
African wild dogs (Lycaon pictus) are highly social canids that live in large, hierarchical packs and engage in coordinated hunts. Recent research has suggested that enlarged muscles associated with expressive movement of the eyes and eyebrows may have evolved in domestic dogs (Canis familiaris) to facilitate interspecies communication with their human owners. In L. pictus, communication is reported to occur predominantly through vocalization with reduced reliance on facial expressions; however, the mimic muscles in L. pictus have never been described and evaluated. L. pictus is also hypercarnivorous with the highest documented bite force quotient of any mammalian carnivore. It has large, mobile ears, which enhance its auditory capabilities while hunting and assist with thermoregulation. We performed detailed dissections of the muscles of facial expression, mastication, and auricular movement in an adult male L. pictus,and conducted diffusible iodine‐based contrast‐enhanced computed tomographic (diceCT) scans of the head. Musculus levator anguli oculi medialis (LAOM) and retractor anguli oculi lateralis (RAOL), muscles of hypothesized importance in domestic dog‐human non‐verbal communication, are enlarged in L. pictus, suggesting that ocular expressions represent a significant component of communication. LAOM exhibits an intricate relationship with adjacent orbital musculature including partial fusion along its borders with mm. orbicularis oculi and frontalis. Muscles that draw the angles of the mouth caudally (e.g., m. zygomaticus major) are expanded. Numerous ramifying branches of CN VII and CN V2 course across the face to provide extensive sensory and motor innervation. These findings indicate that facial expression musculature of African wild dogs is well‐equipped for non‐verbal communication and that the same adaptations argued to facilitate communication between domestic dogs and humans may also facilitate intraspecific communication in L. pictus. Muscles of mastication are especially enlarged in L. pictus, with multiple bellies of mm. masseter and temporalis separated by deep layers of thick intermuscular fascia and with expanded insertions onto the mandible. Musculus digastricus is composed of a single, large belly without intervening tendon, and it receives its innervation exclusively from CN V3. These enlargements reflect increased masticatory capabilities in L. pictus, which enable its powerful bite force and hypercarnivorous diet. Auricular muscles are also well‐developed, supporting greater leverage and fine manipulation of its large, mobile ears. Musculus frontoscutularis is well‐developed and distinctly separable from m. frontalis, suggesting greater leverage of the auricle via attachments to the scutiform cartilage. The intrinsic ear muscles differ in pattern and orientation from all other published canids, demonstrating unique muscular control over rotation and fine manipulation of the auricle. Taken together, these morphological patterns illustrate that specific adaptations in the cranial muscul...
Surgical options for advanced Kienböck’s disease include proximal row carpectomy or lunate reconstruction with a medial femoral trochlea osteochondral flap. This study compares morphology of the proximal capitate and the medial femoral trochlear surfaces to the proximal lunate using three-dimensional geometric morphometric analysis. Virtual articular surfaces were extracted from MRI studies of ten healthy volunteers. Distances between corresponding points on the proximal lunate and proximal capitate or medial femoral trochlear surfaces were measured. In seven subjects, mean inter-surface distance for the medial femoral trochlea–proximal lunate pair was significantly lower than the proximal capitate–proximal lunate pairing. In three subjects, mean proximal capitate–proximal lunate distance was significantly lower. We conclude that the medial femoral trochlear flap was anatomically closer to the shape of the proximal lunate in the majority of the examined subjects. However, we found that in three out of ten cases, the proximal capitate was a better match.
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