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Mammals. Chapter 28. Class Mammalia. Mammals, class Mammalia , are represented by more than 5,000 species. Kitti’s hognosed bat from Thailand weighs 1.5 g. Blue whales exceed 130 metric tons. Derived Characters of Mammals.

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Chapter 28

class mammalia
Class Mammalia
  • Mammals, class Mammalia, are represented by more than 5,000 species.
    • Kitti’s hognosed bat from Thailand weighs 1.5 g.
    • Blue whales exceed 130 metric tons.
derived characters of mammals
Derived Characters of Mammals
  • Mammary glands, which produce milk are a distinctively mammalian character.
  • Hair is another mammalian characteristic.
  • Mammals generally have a larger brain than other vertebrates of equivalent size.
early evolution of mammals
Early Evolution of Mammals
  • Mammals evolved from synapsids in the late Triassic period.
    • The earliest synapsids radiated into diverse herbivorous & carnivorous forms – the pelycosaurs.
early evolution of mammals5
Early Evolution of Mammals
  • One group of carnivorous pelycosaurs led to the therapsids.
    • The only synapsid group to survive into the Mesozoic.
    • Limbs positioned under the body.
early evolution of mammals6
Early Evolution of Mammals
  • Cynodonts were a group of therapsid reptiles that radiated in the Mesozoic.
    • One branch of cynodonts eventually led to the early therians (marsupial and placental mammals).
early evolution of mammals7
Early Evolution of Mammals
  • Cynodonts evolved:
    • A high metabolic rate that supported a more active life.
    • Enhanced jaw musculature
    • A secondary bony palate permits breathing while holding prey or chewing food.
      • Important later to mammal evolution by allowing young to breathe while suckling
early evolution of mammals8
Early Evolution of Mammals
  • Turbinate bones in the nasal cavity aided in the retention of heat.
early evolution of mammals9
Early Evolution of Mammals
  • The jaw was remodeled during the evolution of mammals from nonmammalian synapsids.
    • Two of the bones that formerly made up the jaw joint were incorporated into the mammalian middle ear.
early evolution of mammals10
Early Evolution of Mammals
  • Living lineages of mammals originated in the Jurassic, but did not undergo a significant adaptive radiation until after the Cretaceous.
skin hair
Skin & Hair
  • Skin is composed of the thinner epidermis and the underlying, thicker dermis.
  • Hair is one of the defining characteristics of mammals.
    • Composed of dead, keratin-packed epidermal cells.
  • Two kinds of hair form the coat of most mammals:
    • Dense and soft underhair for insulation.
      • Traps a layer of insulating air.
      • Extremely dense in aquatic mammals.
    • Coarse, longer guard hair for protection from wear and coloration.
  • Mammals shed or molt once or usually twice each year.
    • Summer coat usually thinner.
    • May be a different color.
  • Hair can be specialized into bristles, spines, and whiskers.
    • Whiskers, vibrissae, are sensory hairs that provide tactile sense to many mammals.
      • Especially long in nocturnal and burrowing mammals.
horns antlers
Horns & Antlers
  • Horns, like those of sheep & cattle, are hollow sheaths of keratinized epidermis with a core of bone.
    • Found in both sexes, grow continuously, are not shed.
horns antlers17
Horns & Antlers
  • Antlers, like those of deer, are branched and composed of solid bone.
    • During growth, they have a highly vascular soft skin called velvet covering them.
    • Usually only males have antlers.
      • Both sexes of Caribou have antlers.
  • Mammals have the greatest variety of integumentary glands of any vertebrate.
    • Sweat glands – involved in heat regulation.
    • Scent glands – for marking territories, warning, defense.
    • Sebaceous glands – associated with hair follicles.
    • Mammary glands – provides milk for offspring, gives mammals their name.
food and feeding
Food and Feeding
  • Mammals eat a wide variety of food.
  • Dentition often reflects the food they eat.
  • Heterodont dentition
food and feeding20
Food and Feeding
  • Mammals also have adaptations that help them digest the different types of foods they eat.
    • Herbivores can’t digest cellulose – they rely on microorganisms to metabolize cellulose.
body weight and food consumption
Body Weight and Food Consumption
  • The smaller the animal, the higher its metabolic rate.
    • More food must be consumed.
  • Some terrestrial mammals, like caribou and bison, migrate twice annually between summer and winter ranges.
  • Migration is more common among oceanic whales & seals.
flight and echolocation
Flight and Echolocation
  • Many mammals can glide from tree to tree.
  • Not powered flight.
  • Gliding & flying evolved independently.
flight and echolocation25
Flight and Echolocation
  • Bats have evolved true flight.
  • Mostly nocturnal or crepuscular.
  • Echolocation is used to navigate and locate food.
  • Many mammals defend a territory that includes resources such as food, shelter, or mates that is defended from others usually of the same species (conspecifics) – those that would utilize the same resources.
  • A mammal usually has a larger, undefended home range that may overlap with the home range of conspecifics.
  • Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus.
  • Monotremes are oviparous mammals.
  • Eggs have a thin, leathery shell.
  • Babies hatch in a relatively undeveloped state.
  • Echidnas have an abdominal pouch where they keep the young.
  • Young feed on milk secreted by the mother’s mammary glands.
  • Marsupials include opossums, kangaroos, and koalas.
  • Before it is a born, an embryonic marsupial receives nourishment by absorbing nutrient secretions in the uterus.
  • A marsupial is born very early in its development and completes its embryonic development while nursing within a maternal pouch called a marsupium.
convergent evolution
Convergent Evolution
  • In Australia, convergent evolution has resulted in a diversity of marsupials that resemble eutherians (placental mammals) in other parts of the world.
eutherians placental mammals
Eutherians – Placental Mammals
  • Compared to marsupials, eutherians have a longer period of pregnancy.
    • Usually larger placental mammals have longer gestations.
eutherians placental mammals35
Eutherians – Placental Mammals
  • Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta.
  • The mammalian order Primates include:
    • Lemurs, tarsiers, monkeys, and apes
  • Humans are members of the ape group.
  • Most primates have hands and feet adapted for grasping.
  • Primates also have:
    • A large brain and short jaws.
    • Forward-looking eyes close together on the face, providing depth perception.
    • Well-developed parental care and complex social behavior.
    • A fully opposable thumb.
living primates
Living Primates
  • There are three main groups of living primates:
    • The lemurs of Madagascar and the lorises and pottos of tropical Africa and southern Asia form one group.
living primates39
Living Primates
  • The tarsiers of Southeast Asia.
living primates40
Living Primates
  • The anthropoids, which include monkeys and hominids worldwide.
primate evolution
Primate Evolution
  • The oldest known anthropoid fossils are about 45 million years old.
    • Indicate that tarsiers are more closely related to anthropoids.
primate evolution42
Primate Evolution
  • The fossil record indicates that monkeys first appeared in the New World (South America) during the Oligocene (~36 mya).
  • The first monkeys evolved in the Old World (Africa and Asia) about 40 mya.
primate evolution43
Primate Evolution
  • New World and Old World monkeys underwent separate adaptive radiations during their many millions of years of separation.
primate evolution44
Primate Evolution
  • The other group of anthropoids, the hominoids, consists of primates informally called apes.
  • Hominoids diverged from Old World monkeys about 20–25 million years ago.
primate evolution45
Primate Evolution
  • African apes – chimpanzees & gorillas have been moved into the familyHominidae to more accurately reflect relatedness.
    • So, now, humans, chimps and gorillas are hominids.
  • Many researchers advocate placing them in the genus Homo as well.
humans bipedal hominoids
Humans – Bipedal Hominoids
  • Homo sapiens is about 200,000 years old which is very young considering that life has existed on Earth for at least 3.5 billion years.
derived characters of hominids
Derived Characters of Hominids
  • A number of characters distinguish humans from other hominoids:
    • Upright posture and bipedal locomotion
    • Larger brains
    • Language capabilities
    • Symbolic thought
    • The manufacture and use of complex tools
    • Shortened jaw
human origins
Human Origins
  • The study of human origins is known as paleoanthropology.
  • Paleoanthropologists have discovered fossils of approximately 20 species of extinct hominoids that are more closely related to humans than to chimpanzees.
human origins49
Human Origins

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human origins50
Human Origins
  • Hominins (modern humans and their extinct ancestors are placed in the subfamily Homininae) originated in Africa approximately 6–7 million years ago.
  • Early hominins had a small brain, but probably walked upright, exhibiting mosaic evolution (different traits evolving at different rates).
human origins51
Human Origins
  • Two common misconceptions of early hominids include:
    • Thinking of them as chimpanzees.
    • Imagining human evolution as a ladder leading directly to Homo sapiens.
human origins52
Human Origins
  • Australopiths are a paraphyletic assemblage of hominids that lived between 4 and 2 million years ago.
human origins53
Human Origins
  • Some species walked fully erect and had human-like hands and teeth.
  • Australopith brains were smaller than modern humans, but larger than chimps.
  • Hominins began to walk long distances on two legs about 1.9 million years ago.
tool use
Tool Use
  • The oldest evidence of tool use – cut marks on animal bones – is 2.5 million years old.
early homo
Early Homo
  • The earliest fossils that paleoanthropologists place in our genus, Homo, are those of the species Homo habilis, ranging in age from about 2.4 to 1.6 million years.
  • Stone tools have been found with H. habilis, giving this species its name, which means “handy man”.
early homo57
Early Homo
  • Homo ergasterwas the first fully bipedal, large-brained hominin.
    • Existed between 2 and 1.4 million years.
early homo58
Early Homo
  • Homo erectus originated in Africa approximately 1.8 million years ago.
    • The first hominin to leave Africa.
    • Social – living in tribes of 20-50.
  • Neanderthals, Homo neanderthalensis lived in Europe and the Near East from 200,000 to 30,000 years ago.
    • Large, thick-browed hominins.
    • Became extinct a few thousand years after the arrival of Homo sapiens in Europe.
homo sapiens
Homo sapiens
  • Homo sapiens appeared in Africa at least 200,000 years ago.
homo sapiens61
Homo sapiens
  • The rapid expansion of our species may have been preceded by changes to the brain that made symbolic thought and other cognitive innovations possible.
  • Binocular vision, visuotactile discrimination and manipulative skills that resulted from our arboreal ancestry likely played a role as well.