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).
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 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 locomotion
 Larger brains
 Language capabilities
 Symbolic thought
 The manufacture and use of complex tools
 Shortened 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.