Chapter 20: Mammals


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Describe structural and functional adaptations in early amniotes that foreshadowed the mammalian body plan.
pair of openings in the temporal region of the skull associated with attachment of mandibular muscles; therapsids, the only synapsid group to survive beyond the Paleozoic era. efficient erect gait with upright limbs positioned beneath the body; Since stability was reduced by raising the animal from muscular coordination center of the brain, the cerebellum, assumed an expanded role. increased and specialized jaw musculature, permitting a stronger bite; several skeletal changes, supporting greater agility; heterodont teeth, permitting better food processing; turbinate bones (creates folds in nasal cavity in order to swirl air, to warm up and humidify air before it goes into the lungs) in the nasal cavity, aiding retention of body heat; and a bony, secondary palate; evolution of a diaphragm and also may have provided greater dorsoventral flexibility to the spinal column.
Hair is hypothesized to have evolved in therapsids as an adaptation for insulation, but modern mammals have adapted hair for several other purposes. Describe these.
concealment, behavioral signaling, waterproofing, and buoyancy; sensitive vibrissae, thermal insulation
Horns of bovids
True horns of the family Bovidae (sheep and cattle) are hollow sheaths of keratinized epidermis that embrace a core of bone arising from the skull. True horns aren't shed, usually are not branched ( although they may be greatly curved), grow continuously, and occur in both sexes.
Antlers of deer
branched and composed of solid bone when mature
Horns of rhinos
consists of hairlike, keratinized filaments that arise from dermal papillae cemented together, but they are not attached to the skull.
Describe the growth cycle of antlers
Antlers begin to grow in late spring, stimulated by pituitary gonadotropins. The bone grows very rapidly until halted by a rapid rise in testosterone production by the testes. The skin (velvet) dies and sloughs off. Testosterone levels peak during the fall breeding season. The antlers are shed in January as testosterone levels subside.
Sweat glands (eccrine and apocrine)
are tubular, highly coiled glands. Eccrine glands secrete a watery fluid that draws heat away from the body. Apocrine glands always open into a hair follicle or where a hair once was; develop near sexual puberty and are restricted (in humans) to the axillae (armpits), mons pubis, breasts, prepuce, scrotum, and external auditory canals. milky fluids, whitish or yellow in color that dry on the skin to form a film.
Scent glands
are used for communication with members of the same species, for marking territorial boundaries, for warning, or for defense
Sebaceous glands
Sebum on hair follicles
Mammary glands
In human females, adipose tissue begins to accumulate around mammary glands at puberty to form the breast. In most mammals, milk is secreted from mammary glands
shrews, moles, anteaters, and bats; feed on a variety of insects and other small invertebrates. Most have teeth with pointed cusps, permitting them to puncture the exoskeleton or skin of their prey, some completely lack teeth.
feed on grasses and other vegetation form 2 groups: browsers and grazers, such as ungulates (hooved mammals, including horses, deer, antelope, cattle, sheep, and goats) and gnawers, including many rodents as well as rabbits and hares. Canines are absent or reduced in size, whereas molars, are adapted for grinding, are broad and usually high-crowned. Rodents have chisel-sharp incisors that grow throughout life and must be worn away to keep pace with their continual growth
feed mainly on herbivores. Foxes, dogs, weasels, wolverines, fishers, and cats; well-equipped with biting and piercing teeth and powerful clawed limbs for killing their prey. Since their protein diet is more easily digested than the fibrous food of herbivores, their digestive tract is shorter, and the cecum is small or absent. Carnivores organize their feeding into discrete meals rather than feeding continuously (as do most herbivores) and therefore have much more leisure time
use both plants and animals for food. Examples are pigs, raccoons, many rodents, bears, and most primates, including humans. Also eat fruits, berries, and grasses when hard pressed. Foxes, which usually feed on mice, small rodents, and birds, eat frozen apples, beechnuts, and corn when their normal food sources are scarce
How are the digestive tracts of mammals specialized for symbiotic digestion of cellulose?
harbor anaerobic bacteria and protozoa that produce cellulose in fermentation chambers in their gut. Simple carbohydrates, proteins, and lipids produced by the microorganizms can be adsorbed by the host animal, and the host can digest the microorganisms as well. Ruminants have huge four chambered stomach. As ruminant feeds, grass passes down the esophagus to the rumen, where it is digested by microorganisms and then formed into small balls of cud. At its leisure, the ruminant returns a cud to its mouth and chews it deliberately and at length to crush the fiber. Swallowed again, the food returns to the rumen where the cellulolytic bacteria and protozoa continue fermentation
Explain what is distinctive about the life habit and mode of navigation in bats
flight and the capacity to navigate by echolocation. a bat emits short pulses 5-10 msec in duration in a narrow directed beam from its mouth or nose. Each pulse is frequently modulated; its highest at the beginning, up to 100,000 Hz, and sweeps down to perhaps 30,000 Hz at the end.
Describe and distinguish patterns of reproduction in monotremes, marsupials, and placental mammals
Monotremes are oviparous mammals, such as the duck-billed platypus, which has one breeding season each year. Embryos develop for 10-12 days in the uterus, where they are nourished by yolk supplies deposited prior to ovulation and by secretions from the mother. A thin, leathery shell is secreted around the embryos before the eggs are laid. Because monotremes have no nipples, the young lap milk secreted onto the belly fur of the mother.
Marsupials are pouched, viviparous mammals that exhibit a second pattern of reproduction. Gestation is brief in marsupials, and therefore all marsupials give birth to tiny young that are effectively still embryos, both anatomically and physiologically. However, early birth is followed by prolonged interval of lactation and parental care.
Eutherians. The reproductive investment is in prolonged gestation, unlike marsupials in which the reproductive investment is in prolonged lactation.
What aspects of mammalian reproduction are present in all mammals but in no other vertebrates?
Mammary glands
What anatomical characteristics distinguish primates from other mammals?
Skull; brain
What role does the fossil named "Lucy" play in reconstruction of human evolutionary history?
Was most complete skeleton
In what ways do the genera Australopithecus and Homo, which coexisted for at least 1 million years, differ?
What major attributes make the human position in animal evolution unique?