9/17/2023 0 Comments Australopithecus platypus skullThese bones are present in mammals, but they have been modified to function in hearing and form bones in the middle ear (Figure 1). In mammals, the dentary bone joins the skull at the squamosal bone, while in other vertebrates, the quadrate bone of the jaw joins with the articular bone of the skull. The jaws of other vertebrates are composed of more than one bone. The lower jaw of mammals consists of only one bone, the dentary. The skeletal system of mammals possesses many unique features. Mammary glands likely are modified sebaceous or eccrine glands, but their evolutionary origin is not entirely clear.įigure 1. Bones of the mammalian inner ear are modified from bones of the jaw and skull. While male monotremes and eutherians possess mammary glands, male marsupials do not. Mammary glands produce milk that is used to feed newborns. Apocrine glands, or scent glands, secrete substances that are used for chemical communication, such as in skunks. Sweat glands are located over most of the body surface in primates. However, in primates, especially humans, sweat figures prominently in thermoregulation, regulating the body through evaporative cooling. In most mammals, eccrine glands are limited to certain areas of the body, and some mammals do not possess them at all. Eccrine glands produce sweat, or perspiration, which is mainly composed of water. Sebaceous glands are located over most of the body. Sebaceous glands produce a lipid mixture called sebum that is secreted onto the hair and skin for water resistance and lubrication. Mammalian integument, or skin, includes secretory glands with various functions. Hair can also provide protective coloration or be part of social signaling, such as when an animal’s hair stands “on end.” These attach to nerves that transmit information about sensation, which is particularly useful to nocturnal or burrowing mammals. Along with insulation, hair can serve as a sensory mechanism via specialized hairs called vibrissae, better known as whiskers. Hair traps a layer of air close to the body, retaining heat. Mammals are endothermic, and hair provides insulation to retain heat generated by metabolic work. Although it is not very extensive on certain species, such as whales, hair has many important functions for mammals. The presence of hair is one of the most obvious signs of a mammal. Describe the evolutionary history of humans.Describe the evolutionary history of primates.Describe the evolutionary history of mammals.Name and describe the distinguishing features of the three main groups of mammals.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |