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.
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Characteristics
Hair – for camouflage and
preventative heat loss
 Mammary glands
 Specialized teeth
 Three middle ear bones
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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
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Other Important Orders
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Ungulates – Hoofed animals
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Artiodactyla – even-toed hoofed
animals (horses)
Cetacia – whales and porpoises
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Some have baleen
Chiroptera – bats
 Lagomorphs – rabbits
 Pinnepidia – seals and
walruses
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Teeth
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Mammals are called heterodonts because
they have teeth specialized for different
functions.
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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
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Unlike birds, our
vertebral column is
NOT fused
Divided into
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Cervical – neck
bones; first two are
the atlas & the axis
Thoracic – ribs are
attached
Lumbar – lower back
Circulation
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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
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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
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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
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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.