JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press and Wenner-Gren Foundation for Anthropological Research are collaborating with JSTOR to digitize, preserve and extend access to Current Anthropology.The past 200,000 years of human cultural evolution have witnessed the persistent establishment of behaviors involving innovation, planning depth, and abstract and symbolic thought, or what has been called "behavioral modernity." Demographic models based on increased human population density from the late Pleistocene onward have been increasingly invoked to understand the emergence of behavioral modernity. However, high levels of social tolerance, as seen among living humans, are a necessary prerequisite to life at higher population densities and to the kinds of cooperative cultural behaviors essential to these demographic models. Here we provide data on craniofacial feminization (reduction in average brow ridge projection and shortening of the upper facial skeleton) in Homo sapiens from the Middle Pleistocene to recent times. We argue that temporal changes in human craniofacial morphology reflect reductions in average androgen reactivity (lower levels of adult circulating testosterone or reduced androgen receptor densities), which in turn reflect the evolution of enhanced social tolerance since the Middle Pleistocene.Middle Paleolithic, CTE appears to have accelerated during the interval between about 80 and 30 Ka BP. Beginning sporadically in the later part of the Middle Stone Age (MSA) and continuing with increasing regularity into the Later Stone Age (LSA) and Upper Paleolithic (UP), this interval witnessed the rapid florescence of new technologies, including leptolithic and microlithic tools, greater artifact diversity, bone and antler working, heat treatment and pressure flaking of flint, longrange projectile weapons, grindstones, fishing and birding gear, trapping technology, sophisticated pyrotechnology, and possibly watercraft (Ambrose 1998; Backwell, d'Errico, and Yellen et al. 1995). This period of rapid technological innovation is contemporaneous with the earliest evidence of symbolic behavior and abstract thought, in the form of pigment processing, personal adornment, incised notational pieces, musical instruments, and mobilary and parietal art (Bouzouggar et al.

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Poposaurus gracilis is a bipedal pseudosuchian archosaur that has been poorly understood since the discovery of the holotype fragmentary partial postcranial skeleton in 1915. Poposaurus. gracilis is a member of Poposauroidea, an unusually morphologically divergent clade of pseudosuchians containing taxa that are bipedal, quadrupedal, toothed, edentulous, and some individuals with elongated thoracic neural spines (i.e., sails). In 2003, a well preserved, fully articulated, and nearly complete postcranial skeleton of P. gracilis was discovered with some fragmentary cranial elements from the Upper Triassic Chinle Formation of Grand Staircase‐Escalante National Monument of southern Utah, USA. The aim of this work is to describe the osteology of this specimen in detail and compare P. gracilis to other closely related pseudosuchian archosaurs. The open neurocentral sutures throughout the majority of the vertebral column, the small size of this individual, and the presence of seven evenly spaced cyclic growth marks in the histologically sectioned femur indicate that this specimen was a skeletally immature juvenile, or subadult when it died. The pes of P. gracilis contains multiple skeletal adaptations and osteological correlates for soft tissue structures that support a hypothesis of digitigrady for this taxon. When coupled with the numerous postcranial characters associated with cursoriality, and the many anatomical traits convergent with theropod dinosaurs, this animal likely occupied a similar ecological niche with contemporaneous theropods during the Late Triassic Period. Anat Rec, 303:874–917, 2020. © 2019 American Association for Anatomy

The generally accepted framework for the evolution of a key feature of the avian respiratory system, unidirectional airflow, is that it is an adaptation for efficiency of gas exchange and expanded aerobic capacities, and therefore it has historically been viewed as important to the ability of birds to fly and to maintain an endothermic metabolism. This pattern of flow has been presumed to arise from specific features of the respiratory system, such as an enclosed intrapulmonary bronchus and parabronchi. Here we show unidirectional airflow in the green iguana, a lizard with a strikingly different natural history from that of birds and lacking these anatomical features. This discovery indicates a paradigm shift is needed. The selective drivers of the trait, its date of origin, and the fundamental aerodynamic mechanisms by which unidirectional flow arises must be reassessed to be congruent with the natural history of this lineage. Unidirectional flow may serve functions other than expanded aerobic capacity; it may have been present in the ancestral diapsid; and it can occur in structurally simple lungs.diapsid | evolution | lung | lizard | respiratory system

Mechanisms explaining unidirectional pulmonary airflow in birds, a condition where lung gases flow in a consistent direction during both inspiration and expiration in some parts of the lung, were suggested as early as the first part of the twentieth century and unidirectional pulmonary airflow has been discovered recently in crocodilians and squamates. Our knowledge of the functional anatomy, fluid dynamics, and significance of this trait is reviewed. The preponderance of the data indicates that unidirectional airflow is maintained by means of convective inertia in inspiratory and expiratory aerodynamic valves in birds. The study of flow patterns in non-avian reptiles is just beginning, but inspiratory aerodynamic valving likely also plays an important role in controlling flow direction in these lungs. Although highly efficient counter and cross-current blood-gas exchange arrangements are possible in lungs with unidirectional airflow, very few experiments have investigated blood-gas exchange mechanisms in the bird lung and blood-gas arrangements in the lungs of non-avian reptiles are completely unknown. The presence of unidirectional airflow in non-volant ectotherms voids the traditional hypothesis that this trait evolved to supply the high aerobic demands of flight and endothermy, and there is a need for new scenarios in our understanding of lung evolution. The potential value of unidirectional pulmonary airflow for allowing economic lung gas mixing, facilitating lung gas washout, and providing for adequate gas exchange during hypoxic conditions is discussed.

The structures and functions of the vertebrate lung and trunk are linked through the act of ventilation, but the connections between these structures and functions are poorly understood. We used X-ray reconstruction of moving morphology (XROMM) to measure rib kinematics during lung ventilation in three savannah monitor lizards (Varanus exanthematicus). All of the dorsal ribs, including the floating ribs, contributed to ventilation; the magnitude and kinematic pattern showed no detectable cranial-to-caudal gradient. The true ribs acted as two rigid bodies connected by flexible cartilage, with the vertebral rib and ventromedial shaft of each sternal rib remaining rigid and the cartilage between them forming a flexible intracostal joint. Rib rotations can be decomposed into bucket handle rotation around a dorsoventral axis, pump handle rotation around a mediolateral axis and caliper motion around a craniocaudal axis. Dorsal rib motion was dominated by roughly equal contributions of bucket and pump rotation in two individuals and by bucket rotation in the third individual. The recruitment of floating ribs during ventilation in monitor lizards is strikingly different from the situation in iguanas, where only the first few true ribs contribute to breathing. This difference may be related to the design of the pulmonary system and life history traits in these two species. Motion of the floating ribs may maximize ventilation of the caudally and ventrolaterally positioned compliant saccular chambers in the lungs of varanids, while restriction of ventilation to a few true ribs may maximize crypsis in iguanas.

There is a functional trade-off in the design of skeletal muscle. Muscle strength depends on the number of muscle fibers in parallel, while shortening velocity and operational distance depend on fascicle length, leading to a trade-off between the maximum force a muscle can produce and its ability to change length and contract rapidly. This trade-off becomes even more pronounced as animals increase in size because muscle strength scales with area (length 2) while body mass scales with volume (length 3). In order to understand this muscle trade-off and how animals deal with the biomechanical consequences of size, we investigated muscle properties in the pectoral girdle of varanid lizards. Varanids are an ideal group to study the scaling of muscle properties because they retain similar body proportions and posture across five orders of magnitude in body mass and are highly active, terrestrially adapted reptiles. We measured muscle mass, physiological cross-sectional area, fascicle length, proximal and distal tendon lengths, and proximal and distal moment arms for 27 pectoral girdle muscles in 13 individuals across 8 species ranging from 64 g to 40 kg. Standard and phylogenetically informed reduced major axis regression was used to investigate how muscle architecture properties scale with body size. Allometric growth was widespread for muscle mass (scaling exponent >1), physiological cross-sectional area (scaling exponent >0.66), but not tendon length (scaling exponent >0.33). Positive allometry for muscle mass was universal among muscles responsible for translating the trunk forward and flexing the elbow, and nearly universal among humeral protractors and wrist flexors. Positive allometry for PCSA was also common among trunk translators and humeral protractors, though less so than muscle mass. Positive scaling for fascicle length was not widespread, but common among humeral protractors. A higher proportion of pectoral girdle muscles scaled with positive allometry than our previous work showed for the pelvic girdle, suggesting that the center of mass may move cranially with body size in varanids, or that the pectoral girdle may assume a more dominant role in locomotion in larger species. Scaling exponents for physiological cross-sectional area among muscles primarily associated with propulsion or with a dual role were generally higher than those associated primarily with support | 1115 CIERI Et al.

Although the airways of vertebrates are diverse in shape, complexity, and function, they all contain visceral smooth muscle. The morphology, function, and innervation of this tissue in airways is reviewed in actinopterygians, lungfish, amphibians, non-avian reptiles, birds, and mammals. Smooth muscle was likely involved in tension regulation ancestrally, and may serve to assist lung emptying in fishes and aquatic amphibians, as well as maintain internal lung structure. In certain non-avian reptiles and anurans antagonistic smooth muscle fibers may contribute to intrapulmonary gas mixing. In mammals and birds, smooth muscle regulates airway caliber, and may be important in controlling the distribution of ventilation at rest and exercise, or during thermoregulatory and vocal hyperventilation. Airway smooth muscle is controlled by the autonomic nervous system: cranial cholinergic innervation generally causes excitation, cranial non-adrenergic, non-cholinergic innervation causes inhibition, and spinal adrenergic (SA) input causes species-specific, often heterogeneous contractions and relaxations.