The endocranium and trophic ecology of Velociraptor mongoliensis.

Neuroanatomical reconstructions of extinct animals have long been recognized as powerful proxies for palaeoecology, yet our understanding of the endocranial anatomy of dromaeosaur theropod dinosaurs is still incomplete. Here, we used X-ray computed microtomography (µCT) to reconstruct and describe the endocranial anatomy, including the endosseous labyrinth of the inner ear, of the small-bodied dromaeosaur, Velociraptor mongoliensis. The anatomy of the cranial endocast and ear were compared with non-avian theropods, modern birds, and other extant archosaurs to establish trends in agility, balance, and hearing thresholds in order to reconstruct the trophic ecology of the taxon. Our results indicate that V. mongoliensis could detect a wide and high range of sound frequencies (2,368-3,965 Hz), was agile, and could likely track prey items with ease. When viewed in conjunction with fossils that suggest scavenging-like behaviours in V. mongoliensis, a complex trophic ecology that mirrors modern predators becomes apparent. These data suggest that V. mongoliensis was an active predator that would likely scavenge depending on the age and health of the individual or during prolonged climatic events such as droughts.

A reinterpretation of human breast anatomy includes all the layers of the anterior body wall.

Mammary glands define mammals as a group, yet a comprehensive anatomical description of the mammary gland does not exist for almost any mammalian species. In humans, the anatomical and surgical literature provide conflicting and incomplete descriptions of the gross anatomy of the breast. We dissected 9 male and 15 female human body donors to clarify this gross anatomy. We found that, like other epidermally derived glands of the body, the mammary glandular tissue is constrained to a membrane-bound, central structure referred to as the corpus mammae in the surgical literature, and not dispersed throughout the breast as typically described in the anatomical literature. The major fasciae of the human anterior body wall, including the superficial fatty Camper's fascia and the deeper membranous Scarpa's fascia, both contribute to the structure of the breast. This anatomical arrangement suggests that, as the mammary gland invaginates posteriorly from the integument during embryological development, the mammary fat pad most likely derives from Camper's fascia, and growth of Scarpa's fascia around this fat pad forms the anterior and posterior lamellae of the breast pocket. Anteriorly, Scarpa's fascia becomes a double layer that creates the surface structure of the breast. Posteriorly, Scarpa's fascia forms a circummammary ligament that (1) stabilizes the breast against the thoracic wall and (2) is continuous with Scarpa's fascia on the rest of the anterior body wall. The suspensory ligaments of the breast represent the typical retinaculae cuti found consistently throughout the human body wall, and do not directly attach to the skin. Instead, these retinaculae attach to the anterior or posterior lamella of Scarpa's fascia.

Evolution of vision and hearing modalities in theropod dinosaurs.

Owls and nightbirds are nocturnal hunters of active prey that combine visual and hearing adaptations to overcome limits on sensory performance in low light. Such sensory innovations are unknown in nonavialan theropod dinosaurs and are poorly characterized on the line that leads to birds. We investigate morphofunctional proxies of vision and hearing in living and extinct theropods and demonstrate deep evolutionary divergences of sensory modalities. Nocturnal predation evolved early in the nonavialan lineage Alvarezsauroidea, signaled by extreme low-light vision and increases in hearing sensitivity. The Late Cretaceous alvarezsauroid Shuvuuia deserti had even further specialized hearing acuity, rivaling that of today's barn owl. This combination of sensory adaptations evolved independently in dinosaurs long before the modern bird radiation and provides a notable example of convergence between dinosaurs and mammals.

Turning semicircular canal function on its head: dinosaurs and a novel vestibular analysis.

Previous investigations have correlated vestibular function to locomotion in vertebrates by scaling semicircular duct radius of curvature to body mass. However, this method fails to discriminate bipedal from quadrupedal non-avian dinosaurs. Because they exhibit a broad range of relative head sizes, we use dinosaurs to test the hypothesis that semicircular ducts scale more closely with head size. Comparing the area enclosed by each semicircular canal to estimated body mass and to two different measures of head size, skull length and estimated head mass, reveals significant patterns that corroborate a connection between physical parameters of the head and semicircular canal morphology. Head mass more strongly correlates with anterior semicircular canal size than does body mass and statistically separates bipedal from quadrupedal taxa, with bipeds exhibiting relatively larger canals. This morphologic dichotomy likely reflects adaptations of the vestibular system to stability demands associated with terrestrial locomotion on two, versus four, feet. This new method has implications for reinterpreting previous studies and informing future studies on the connection between locomotion type and vestibular function.

The earliest known eutherian mammal.

The skeleton of a eutherian (placental) mammal has been discovered from the Lower Cretaceous Yixian Formation of northeastern China. We estimate its age to be about 125 million years (Myr), extending the date of the oldest eutherian records with skull and skeleton by about 40 50 Myr. Our analyses place the new fossil at the root of the eutherian tree and among the four other known Early Cretaceous eutherians, and suggest an earlier and greater diversification of stem eutherians that occurred well before the molecular estimate for the diversification of extant placental superorders (104 64 Myr). The new eutherian has limb and foot features that are known only from scansorial (climbing) and arboreal (tree-living) extant mammals, in contrast to the terrestrial or cursorial (running) features of other Cretaceous eutherians. This suggests that the earliest eutherian lineages developed different locomotory adaptations, facilitating their spread to diverse niches in the Cretaceous.