Mammals - PBworks
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Transcript Mammals - PBworks
Mammals:
Specialized Teeth, Endothermy,
& Hair
Speculations…
Mammals began to evolve about 70 mya
during the Tertiary period.
The first mammals were small (less than
10cm.) and were nocturnal
They probably looked like little rodents.
Early mammals were thought to have
avoided competing with dinosaurs
by feeding on insects at night.
Characteristics
Hair – for camouflage and
preventative heat loss
Mammary glands
Specialized teeth
Three middle ear bones
Major Orders…
Monotremes – egg laying mammals;
viviparous (eggs develop inside)
Marsupials – pouched mammals
Placentals – mammals that carry their
babies in a uterus, nourished through
the placenta, and give birth to live
young Ex. primates
Other Important Orders
Ungulates – Hoofed animals
Artiodactyla – even-toed hoofed
animals (horses)
Cetacia – whales and porpoises
Some have baleen
Chiroptera – bats
Lagomorphs – rabbits
Pinnepidia – seals and
walruses
Teeth
Mammals are called heterodonts because
they have teeth specialized for different
functions.
Incisors – used for biting and/or gnawing
Canines – used for tearing meat
Premolars – used for chewing
Molars – used for grinding and chewing
Mammals have 2 sets of teeth in their
lifetime: deciduous teeth and permanent
teeth
Vertebral Divisions in
Mammals
Unlike birds, our
vertebral column is
NOT fused
Divided into
Cervical – neck
bones; first two are
the atlas & the axis
Thoracic – ribs are
attached
Lumbar – lower back
Circulation
Mammals have a 4chambered heart,
separating the two
atria from the two
ventricles.
Remember, veins
return blood TO the
heart, arteries take
blood away FROM the
heart to the rest of the
body; Pulmonary
vessels carry blood to
and from the lungs.
Nutrition & Digestion
Most mammals (including us) currently
have, or have had in the past, a cecum; a
fermentation pouch full of microorganisms
used to digest tough plant matter.
In humans, the cecum has become the
appendix.
Some mammals (cows) have chambered
stomachs. These chambers are called
rumen.
Gas Exchange
Mammals are the
only animals with a
diaphragm, which
prompts to enter
the lungs.
Instead of air sacs,
mammals have
alveoli to increase
surface area.
Nervous System
The size of
mammalian brains
is considerably
large due the
increased size of
the cerebrum.
Cerebrum allows
for more intricate
motor, sensory, and
intellectual
function.