|
Mammals are warm-blooded vertebrates that nurse their young
with milk. They evolved from reptiles. The right and left sides
of the 4-chambered heart are completely separate. The Primates are the mammalian order to which we belong. Most primate characteristics arose as adaptations to life in trees. These features include grasping hands and feet, opposable thumbs, reliance on vision, expansion of the brain, higher intelligence, increased emphasis on learned behavior, single births, and greatly increased parental care. The group to which we belong, the catarrhines, have protruding noses, reduced tails, and only two premolars in each jaw. Humans walk upright. The many consequences of this include tool use, speech, and anatomical changes such as an S-shaped vertebral column (with a lumbar curve) and a more rounded cranium from which the spinal cord exits at the bottom. Class Mammalia: Vertebrates covered with insulation, usually hair or fur (occasionally blubber). Metabolic rates and body temperatures are kept high (homeothermy). Glands in skin secrete sweat and oily secretions (sebum). Young mammals are nursed by their mothers; milk is secreted by mammary glands, derived from sweat glands. Frequent parental care. Normal standing posture keeps the body elevated from the ground, compared to the low-slung posture of amphibians and reptiles. Three tiny ossicles (malleus, incus, stapes) transmit sounds in middle ear. Four-chambered heart has complete separation of oxygen-rich and oxygen-poor blood. Only one bone, the dentary, makes up the lower jaw on each side. A muscular diaphragm is responsible for most breathing movements. A bony hard palate separates nasal cavity from oral cavity, allowing breathing and chewing at the same time. Teeth vary in shape with their position in the mouth and are restricted to only two waves of growth and replacement instead of many. Brain and braincase larger than in reptiles. Origin of mammals: Mammals evolved during Triassic times from mammal-like reptiles (Synapsida). The transition involved changes in the teeth and tooth replacement, the replacement of one jaw hinge (between articular and quadrate bones) with another (between dentary and squamosal bones), and the conversion of the articular and quadrate bones into the malleus and incus. Monotremata: Egg-laying mammals. Example: platypus. Marsupials: Pouched mammals. Examples: kangaroo, opossum. Placental mammals (Eutheria): Mammals in which the fetus is nourished in utero by a placenta. Includes the vast majority of mammals, arranged in over 30 orders, about half extinct and half with living members. Examples: shrews, mice, bats, rats, cows, deer, pigs, dogs, cats, monkeys, humans, whales, horses, elephants, rabbits. Among the many orders of placental mammals are these:
Mammals B Order Primates: Monkeys, apes, humans, lemurs, tarsiers, and related animals. Primate characteristics, mostly related to arboreal adaptations (life in the trees):
Lemuroidea or Strepsirhini: Lemurs, lorises, and galagos. Tarsioidea: Tarsius and its extinct relatives. Platyrrhina: New World monkeys and marmosets, with 3 premolars in each jaw, flat noses, and strong tails that aid in locomotion. Catarrhina: Old World monkeys, apes (gibbons, orangutan, gorilla, chimpanzee) and humans, with 2 premolars in each jaw, protruding noses (nostrils opening downward), and reduced tails, native to Africa, Asia, and Europe. Family Hominidae (humans): Catarrhine primates distinguished from apes (fam. Pongidae) principally by upright locomotion. Characteristics include: Origin of Hominidae: Approximately 5-6 million years ago when upright posture was attained. Human footprints at Laetoli, Kenya, are 4.1 million years old. Evolutionary "dead ends": A number of hominid fossils are now considered to be evolutionary "dead ends," not ancestral to modern humans. These include Sahelanthropus, Ororrin, Kenyapithecus, Ardipithecus, and the large or "robust" Australopithecus robustus and A. boisei. Australopithecus: The best-known early hominids, from South Africa and East Africa. Certain early species (Australopithecus anamensis, A. afarensis) may have been ancestral to Homo, but later species were not. One nearly complete skeleton of A. afarensis, nicknamed "Lucy," was only about 4 feet tall and walked upright. Homo habilis: An East African contemporary of Australopithecus, from about 4 to 1.5 million years ago. Body size about 4 feet tall. Perhaps responsible for early stone tools. Homo erectus: Lived in the middle Pleistocene, after the extinction of Australopithecus. Fossils known from Europe, Africa, Asia. In a cave near Beijing, China, heat-fractured rocks show that fire was used. Homo sapiens: First appeared in the late part of the Ice Age. Taller skull than earlier species. Used more advanced tools. Invented agriculture around 8,000 years ago. |
| Prev | rev. Mar. 2016 | Next |