Class Mammalia
mammals
Class Mammalia
• Origins and Relationships
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Therapsids- in early Mesozoic (approx. 230 mya)
Reptiles with mammal-like characteristics
limbs directly under body not lateral; provided speed
Cerebellum- became expanded and took on greater role;
muscular coordination
separation of food and air passages;
• made possible prolonged chewing;
• animal could hold food in mouth and still breathe
• developed hair
• developed mammary glands
Class Mammalia
• When dinosaurs vanished mammals
suddenly expanded
• Lack of competition allowed for mammal
expansion
• about 70 mya (beginning of Cenozoic)
marks beginning of the age of mammals
• About 55 to 30 mya mammals reached
their peak
Class Mammalia
Characteristics
• Body covered with
hair (function is to
conserve body heat)
– may be reduced in
some species
• Integument (skin)
with a variety of
glands:
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Sweat
Scent
Sebaceous
lacrimal,
mammary glands
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Glands
– Sweat Glands
• keep organism cool
• Two Types
– Eccrine Glands – Watery Sweat
– Apocrine Glands –Milk like sweat
(attracting mates – pheromones)
– Scent Glands• used for attraction of mates
• and to warn of possible enemies,
• to set territories
– Sebaceous Glands- Oil glands;
• used to keep skin soft
• and hair flexible
– Mammary Glands
• modified sweat glands;
• rudimentary in males
• used to feed young
Class Mammalia
characteristics
• Important skeletal
features include:
• two occipital condyles
• head held up off ground
• seven cervical
vertebrae
• ribs attached to
thoracic vertebrae
• often with elongated
tail
• limbs under body
• body held off ground
Class Mammalia
characteristics
• Teeth
– Mouth with heterodont
teeth (differentiated for
different functions);
– have diphyodont teeth
(i.e., two sets-baby and
adult);
– lower jaw a single
enlarged bone-dentary
• Teeth absent in baleen
whales
Class Mammalia
characteristics
• Moveable eyelids and fleshy outer ears
• four limbs (tetrapod)
• Four chambered heart;
Has lungs and voice box;
– separation of food and air passages;
– muscular diaphragm separates thoracic and
abdominal cavities,
– improves efficiency of breathing
• Metanephritic kidney that usually opens
to a bladder
Class Mammalia
characteristics
• Brain highly
developed;
– 12 pairs of
cranial
nerves
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS
OF MAMMALS
• Integument (epidermis
and dermis) and its
derivatives
• Hair; characteristic feature
of all mammals; in some it is
reduced (humans, whales)
• two kinds of hair forming
pelage or fur
– under hair- provides insulation
– guard hair- provides protection
and coloration
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS
OF MAMMALS
• Horns and Antlers
• true horns- found in
ruminants (sheep and cattle)
• hollow sheaths of keratin
anchored to core of bone on
skull
• not normally shed or
branched
• found in both sexes
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS
OF MAMMALS
• Antlers- in the deer family
are entirely of bone material
• develop beneath a covering of highly
vascular tissue called "velvet"
• growth stops during breeding season and
male tears off velvet against tree
• antlers dropped after breeding season,
and a new set starts to develop each year
getting bigger
• in large species this represents as
much as 50 lbs of calcium salts
that is gotten from diet
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS
OF MAMMALS
• Rhinoceros horn
• third kind of horn
• from hairlike horny
fibers from dermis
that are cemented
together
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Feeding Specializations
• Herbivores- two groups; teeth specialized for
shredding, grinding
• all have to deal with cellulose
– ruminants deal with it with four chambered stomach
– • rumen
• reticulum
• omasum
• obomasum
• Carnivores- teeth modified for ripping and tearing
• Omnivores- teeth modified to handle both animal
and plant food
• Insectivores• Filter Feeders- Baleen Whales
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Migration found in some species not all
• Harder for most mammals than birds
• primarily because of locomotion on land
• Prime example is the caribou- migrates about 700
miles twice annually;
• summer range further north where calving takes place;
• winter range to the south where food is, not so cold
• longest mammal migrations done by seals and
whales- easier time of it than land mammals
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Flight
• Bats only mammals that can fly
• wings of bats and birds homologous
• some others may glide- such as flying
squirrel, not true flight;
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Echolocation (bats & marine mammals)
• Bats capable of echolocation;
• emission of sounds that bounce off things as they
echo back bats able to pick them up
• allows them to locate objects without actually seeing
them
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Reproduction- most have definite
breeding season
– males capable of fertile copulation anytime
– females mating function of periodic cycle
called estrus cycle;
• receptive to male only during estrus or heat
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Frequency of estrus species specific
– Monestrus
• one estrus cycle per year
• dogs, foxes, bats
– Polyestrus
• have several estrus cycles per year
• mice, squirrels and many tropical mammals
– Menstrual Cycle - typical of old world monkeys and
humans;
• Follows lunar cycle
• postovulation period results in mentruation -discharge of lining
of uterus
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Patterns of Reproduction
– Monotremes
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Egg laying
found in Australia
ex. duck billed platypus;
eggs fertilized then shell is put around them and
they are buried;
• after hatching mother feeds them with milk
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Patterns of Reproduction
– Marsupials• eggs fertilized
• and early development in uterus (33 days);
• then fetus leaves uterus and travels to pouch and
hooks onto nipple and continues development there
(200+ days)
Class Mammalia
STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF
MAMMALS
• Patterns of Reproduction
– Placentals- (Eutheria)
• most successful mammal groups;
• fertilization, development in uterus;
• gestation period varies with species;
– ex. mice 21 days, cattle 280 days, elephants 22 months;
– generally gestation longer in bigger animals;
– exception are the whales- gestation about 12 month
Class Mammalia
higher classification
• Subclass Protheria
– Order Monotremata
• Subclass Theria
– Infraclass Metetheria (Marsupials)
– Infraclass Eutheria (Placentals)