mammals chapter 28. class mammalia mammals, class mammalia, are represented by more than 5,000...
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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
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
Mammals evolved from synapsids in the late Triassic period.The earliest synapsids radiated into diverse
herbivorous & carnivorous forms – the pelycosaurs.
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 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).
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 Mammals
Early Evolution of Mammals
Turbinate bones in the nasal cavity aided in the retention of heat.
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 Mammals
Living lineages of mammals originated in the Jurassic, but did not undergo a significant adaptive radiation until after the Cretaceous.
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.
Hair
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.
Hair
Mammals shed or molt once or usually twice each year. Summer coat
usually thinner. May be a different
color.
Hair
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, 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 & 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.
Glands
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
Mammals eat a wide variety of food.
Dentition often reflects the food they eat.
Heterodont dentition
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
The smaller the animal, the higher its metabolic rate. More food must be
consumed.
Migration
Some terrestrial mammals, like caribou and bison, migrate twice annually between summer and winter ranges.
Migration
Migration is more common among oceanic whales & seals.
Flight and Echolocation
Many mammals can glide from tree to tree.
Not powered flight.
Gliding & flying evolved independently.
Flight and Echolocation
Bats have evolved true flight. Mostly nocturnal or crepuscular. Echolocation is used to navigate and locate
food.
Territoriality
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.
Territoriality
A mammal usually has a larger, undefended home range that may overlap with the home range of conspecifics.
Monotremes
Monotremes are a small group of egg-laying mammals consisting of echidnas and the platypus.
Monotremes
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
Marsupials include opossums, kangaroos, and koalas.
Marsupials
Before it is a born, an embryonic marsupial receives nourishment by absorbing nutrient secretions in the uterus.
Marsupials
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
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
Compared to marsupials, eutherians have a longer period of pregnancy. Usually larger
placental mammals have longer gestations.
Eutherians – Placental Mammals
Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta.
Primates
The mammalian order Primates include:Lemurs, tarsiers, monkeys, and apes
Humans are members of the ape group.
Primates
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
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 Primates
The tarsiers of Southeast Asia.
Living Primates
The anthropoids, which include monkeys and hominids worldwide.
Primate Evolution
The oldest known anthropoid fossils are about 45 million years old. Indicate that
tarsiers are more closely related to anthropoids.
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 Evolution
New World and Old World monkeys underwent separate adaptive radiations during their many millions of years of separation.
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 Evolution
African apes – chimpanzees & gorillas have been moved into the family Hominidae 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
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
A number of characters distinguish humans from other hominoids:Upright posture and bipedal locomotionLarger brainsLanguage capabilitiesSymbolic thoughtThe manufacture and use of complex toolsShortened jaw
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 Origins
October 2, 2009 issue of Science is full of articles on Ardipithicus ramidus. Available for free! http://www.sciencemag.org/ardipithecus/
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 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 Origins
Australopiths are a paraphyletic assemblage of hominids that lived between 4 and 2 million years ago.
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.
Bipedalism
Hominins began to walk long distances on two legs about 1.9 million years ago.
Tool Use
The oldest evidence of tool use – cut marks on animal bones – is 2.5 million years old.
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 Homo
Homo ergaster was the first fully bipedal, large-brained hominin. Existed between 2
and 1.4 million years.
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
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 appeared in Africa at least 200,000 years ago.
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.