Adaptations to sociality in the mimetic and auricular musculature of the African wild dog (Lycaon pictus).

The African wild dog (Lycaon pictus) is a highly social canid that engages in sophisticated, coordinated group hunting tactics to procure large game. It is one of the most effective hunters of the African savannah, due to its highly developed communication methods. It also has large, mobile ears which enhance its auditory capabilities while hunting and assist with thermoregulation. Recent research suggested that certain muscles of facial expression, particularly those involved with expressive eyebrow movement, evolved solely in domestic dogs (Canis familiaris) to facilitate communication with their human owners. However, it is unclear whether highly social wild canid species may also employ similar expressive eye communication. We performed detailed dissections of an adult male L. pictus to evaluate and describe its mimetic and auricular musculature. Overall, L. pictus has well-developed facial and ear muscles. Musculi levator anguli oculi medialis (LAOM) and retractor anguli oculi lateralis (RAOL), mimetic muscles of hypothesized importance in domestic dog-human non-verbal communication, are enlarged in L. pictus, comparable in size to those of domestic dogs, as is m. orbicularis oculi. This morphology suggests that ocular facial expressions contribute to within-pack communication in wild dogs and are not unique to domestic dogs. The auricular muscles of L. pictus are well-developed, supporting greater leverage and fine manipulation of its large, mobile ears. These muscular adaptations facilitate the highly social ecology of African wild dogs and challenge current interpretations about the unique nature of domestic dog facial expressions.

Relative Brain Volume of Carnivorans Has Evolved in Correlation with Environmental and Dietary Variables Differentially among Clades.

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 (phylogenetic generalized least-squares residual from species' mean body mass) and 9 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.

Medial femoral trochlea flap reconstruction versus proximal row carpectomy for Kienböck's disease: a morphometric comparison.

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.

Appendicular skeletal morphology of North American Martes reflect independent modes of evolution in conjunction with Pleistocene glacial cycles.

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.

Crocodylian Head Width Allometry and Phylogenetic Prediction of Body Size in Extinct Crocodyliforms.

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 R 2≥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.

Alometría del Ancho de la Cabeza de Cocodrilo y Predicción Filogenética del Tamaño Corporal en Cocodrilos Extintos (Crocodylian Head Width Allometry and Phylogenetic Prediction of Body Size in Extinct Crocodyliforms)El tamaño corporal y los cambios de tamaño corporal afectan ampliamente los parámetros de la historia de vida de todos los animales, lo que ha hecho que las estimaciones precisas del tamaño corporal de los taxones extintos sean un componente importante para comprender su paleobiología. Entre los crocodilianos extintos y sus precursores (por ejemplo, los suquios), se han desarrollado varios métodos para predecir el tamaño corporal a partir de conjuntos de indicadores de tejido duro. Sin embargo, muchos tienen aplicaciones limitadas debido a la disparidad de algunos grupos importantes de crocodiliformes y sesgos en el registro fósil. Aquí, probamos la utilidad del ancho de la cabeza como un estimador de tamaño corporal ampliamente aplicable en crocodiliformes vivos y fósiles. Utilizamos un conjunto de datos de individuos machos y hembras sexualmente maduros (n=76) de una muestra exhaustiva de especies existentes de cocodrilos que abarcan casi todos los taxones conocidos (n=22) para desarrollar un modelo filogenético bayesiano y predecir tres métricas convencionales para el tamaño: masa corporal, longitud del orificio de ventilación y longitud total. Luego usamos el modelo para estimar los parámetros de tamaño para una serie selecta de crocodiliformes extintos con afinidad filogenética conocida (Montsechosuchus, Diplocynodon, y Sarcosuchus). Luego comparamos nuestros resultados con los tamaños reportados en la literatura para demostrar la utilidad de nuestro enfoque en una gama amplia de tales fósiles. Nuestros resultados muestran que el ancho de la cabeza está altamente correlacionado con todas las otras métricas (todo R 2≥0.85) y es conmensurable a las dimensiones femorales debido a su confiabilidad como predictor del tamaño corporal. Proporcionamos el código R para permitir que otros investigadores empleen el modelo en su propia investigación.Translated to Spanish by C.A. Alfonso (calfonsoc@vt.edu).