Prolonged or perpetual growth of replacement teeth in the rock hyrax.

Tusks are ever-growing teeth present in mammals of the clade Paenungulata. Unlike the perpetually growing incisors of rodents, tusks are not used in mastication, and in at least some paenungulatans, the tusk is composed of dentin alone in adults. Few studies have provided tissue-level information on tusks of adult paenungulatans with embedding techniques that identify epithelial and other soft tissues.

Evolutionary divergence of facial muscle physiology between domestic dogs and wolves.

Domestic dogs (Canis familiaris) are descended from gray wolf (Canis lupus) populations that inhabited Western Europe and Siberia. The specific timing of dog domestication is debated, but archeological and genetic evidence suggest that it was a multi-phase process that began at least 15,000 years ago. There are many morphological differences between dogs and wolves, including marked divergence in facial muscle morphology, but we know little about the comparative physiology of these muscles.

Dental caries in living and extinct strepsirrhines with insights into diet.

Dental caries is one of the most common diseases afflicting modern humans and occurs in both living and extinct non-human primates, as well as other mammalian species. Compared to other primates, less is known about the etiology or frequency of caries among the Strepsirrhini. Given the link between caries and diet, caries frequency may be informative about the dietary ecology of a given animal.

Mammalian facial muscles contain muscle spindles.

Muscle spindles are sensory receptors in skeletal muscle that provide information on muscle length and velocity of contraction. Previous studies noted that facial muscles lack muscle spindles, but recent reports indicate that the human platysma muscle and "buccal" muscles contain spindles. Mammalian facial muscles are active in social communication, vibrissa movement, and vocalizations, including human speech.

CalliFACS: The common marmoset Facial Action Coding System.

Facial expressions are subtle cues, central for communication and conveying emotions in mammals. Traditionally, facial expressions have been classified as a whole (e.g.

Variation in Ontogenetic Facial Suture Fusion Patterns in Catarrhines.

Timing of craniofacial suture fusion is important for the determination of demographics and primate ontogeny. There has been much work concerning the timing of fusion of calvarial sutures over the last century, but little comprehensive work focusing on facial sutures. Here we assess the relationships of facial suture fusion across ontogeny among select catarrhines.

Anatomical and ontogenetic influences on muscle density.

Physiological cross-sectional area (PCSA), an important biomechanical variable, is an estimate of a muscle's contractile force potential and is derived from dividing muscle mass by the product of a muscle's average fascicle length and a theoretical constant representing the density of mammalian skeletal muscle. This density constant is usually taken from experimental studies of small samples of several model taxa using tissues collected predominantly from the lower limbs of adult animals. The generalized application of this constant to broader analyses of mammalian myology assumes that muscle density (1) is consistent across anatomical regions and (2) is unaffected by the aging process.

Cranial synchondroses of primates at birth.

Cranial synchondroses are cartilaginous joints between basicranial bones or between basicranial bones and septal cartilage, and have been implicated as having a potential active role in determining craniofacial form. However, few studies have examined them histologically. Using histological and immunohistochemical methods, we examined all basicranial joints in serial sagittal sections of newborn heads from nine genera of primates (five anthropoids, four strepsirrhines).

Visualization and quantification of mimetic musculature via DiceCT.

The muscles of facial expression are of significant interest to studies of communicative behaviors. However, due to their small size and high integration with other facial tissues, the current literature is largely restricted to descriptions of the presence or absence of specific muscles. Using diffusible iodine-based contrast-enhanced computed tomography (DiceCT) to stain and digitally image the mimetic mask of (the blue-eyed black lemur), we demonstrate-for the first time-the ability to visualize these muscles in three-dimensional space and to measure their relative volumes.

A Novel Method for Assessing Enamel Thickness Distribution in the Anterior Dentition as a Signal for Gouging and Other Extractive Foraging Behaviors in Gummivorous Mammals.

Gummivory poses unique challenges to the dentition as gum acquisition may often require that the anterior teeth be adapted to retain a sharp edge and to resist loading because they sometimes must penetrate a highly obdurate substrate during gum extraction by means of gouging or scraping. It has been observed previously that the enamel on the labial surface of the teeth used for extraction is thicker relative to that on the lingual surface in taxa that extract gums, while enamel is more evenly distributed in the anterior teeth of taxa that do not regularly engage in extractive behaviors. This study presents a quantitative methodology for measuring the distribution of labial versus lingual enamel thickness among primate and marsupial taxa in the context of gummivory.

Evolution of facial muscle anatomy in dogs.

Domestication shaped wolves into dogs and transformed both their behavior and their anatomy. Here we show that, in only 33,000 y, domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. Based on dissections of dog and wolf heads, we show that the levator anguli oculi medialis, a muscle responsible for raising the inner eyebrow intensely, is uniformly present in dogs but not in wolves.

Vertical Clinging and Leaping Ahead: How Bamboo Has Shaped the Anatomy and Physiology of Hapalemur.

Hapalemur sps. and Prolemur simus (bamboo lemurs, collectively) stand out from the relatively homogeneous lemurids because they are bamboo feeders and vertical clingers and leapers. This unique diet presents equally unique challenges, like its verticality, toughness, and toxicity.

Reverse Dissection and DiceCT Reveal Otherwise Hidden Data in the Evolution of the Primate Face.

Facial expressions, or facial displays, of social or emotional intent are produced by many mammalian taxa as a means of visually communicating with conspecifics at a close range. These displays are achieved by contraction of the mimetic muscles, which are skeletal muscle attached to the dermis of the face. Reverse dissection, removing the full facial mask from the skull and approaching mimetic muscles in reverse, is an effective but destructive way of revealing the morphology of mimetic muscles but it is destructive.

Dental Signatures for Exudativory in Living Primates, with Comparisons to Other Gouging Mammals.

Exudativory, the consumption of gums, is an obligate or a facultative dietary niche for some primates and marsupials. Exudativory has been cited as a dietary niche that may have been present in early primates, so finding a dental signature for exudativory is highly desirable. The present study combines exudativorous lorisoids (galagos and lorises) into one sample to compare to closely related, non-exudativorous lorisoids to search for a consistent dental signature of exudativory.

How the Brain May Have Shaped Muscle Anatomy and Physiology: A Preliminary Study.

Skeletal muscle fibers are often used to evaluate functional differences in locomotion. However, because there are energetic differences among muscle fiber cells, muscle fiber composition could be used to address evolutionary questions about energetics. Skeletal muscle is composed of two main types of fibers: Type I and II.

Functional Morphology of Mimetic Musculature in Primates: How Social Variables and Body Size Stack up to Phylogeny.

Mammalian skeletal muscle is influenced by the functional demands placed upon it. Functional morphology of facial expression musculature, or mimetic musculature, is largely unknown. Recently, primate mimetic musculature has been shown to respond to demands associated with social factors.

Growth and Development at the Sphenoethmoidal Junction in Perinatal Primates.

Integration of the sphenoid and ethmoid bones during early postnatal development is poorly described in the literature. A uniquely prolonged patency of sphenoethmoidal synchondrosis or prespheno-septal synchondrosis (PSept) has been attributed to humans. However, the sphenoethmoidal junction has not been studied using a comparative primate sample.

Eye Size and Set in Small-Bodied Fossil Primates: A Three-Dimensional Method.

We introduce a new method to geometrically reconstruct eye volume and placement in small-bodied primates based on the three-dimensional contour of the intraorbital surface. We validate it using seven species of living primates, with dry skulls and wet dissections, and test its application on seven species of Paleogene fossils of interest. The method performs well even when the orbit is damaged and incomplete, lacking the postorbital bar and represented only by the orbital floor.

Membranous Support for Eyes of Strepsirrhine Primates and Fruit Bats.

Living primates have relatively large eyes and support orbital tissues with a postorbital bar (POB) and/or septum. Some mammals with large eyes lack a POB, and presumably rely on soft tissues. Here, we examined the orbits of four species of strepsirrhine primates (Galagidae, Cheirogaleidae) and three species of fruit bats (Pteropodidae).

The Mobility of the Human Face: More than Just the Musculature.

The human face has the greatest mobility and facial display repertoire among all primates. However, the variables that account for this are not clear. Humans and other anthropoids have remarkably similar mimetic musculature.

Rescue of Premature Coronal Suture Fusion with TGF-β2 Neutralizing Antibody in Rabbits with Delayed-Onset Synostosis.

Objectives: An overexpression of Tgf-β2 leads to calvarial hyperostosis and suture fusion in individuals with craniosynostosis. Inhibition of Tgf-β2 may help rescue fusing sutures and restore normal growth. The present study was designed to test this hypothesis.

Mimetic Muscles in a Despotic Macaque (Macaca mulatta) Differ from Those in a Closely Related Tolerant Macaque (M. nigra).

Facial displays (or expressions) are a primary means of visual communication among conspecifics in many mammalian orders. Macaques are an ideal model among primates for investigating the co-evolution of facial musculature, facial displays, and social group size/behavior under the umbrella of "ecomorphology". While all macaque species share some social behaviors, dietary, and ecological parameters, they display a range of social dominance styles from despotic to tolerant.