Biology 201 Dr' Edwin DeMont

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Biology 201Dr. Edwin DeMont
Chapter 22 Mammals Specialized Teeth, Hair,
Endothermy and Viviparity Part 1
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Mammals
Mammals are distributed on all continents except
Antarctica, and they live in all oceans.
Some of the most distinctive features of mammals
involve adaptations of the epidermis and the
skeletal system.
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Epidermis
Notable features of mammalian skin are - Hair
(with arrector pili muscle)- Large variety of
epidermal glands- Highly stratified epidermis.
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Epidermis Hair
Hair is a unique mammalian structure. The purpose
of hairs includes conservation of body heat,
protection (porcupine quills), warning coloration
(rump patches on antelopes), camouflage (baby
deer), and sensation (whiskers or vibrissae on
carnivores).
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Epidermis Hair
The sea otter has the greatest number of hairs
per area of skin, important in insulating this
marine mammal. Otters have 100,000 hairs/cm2
compare to a dog with 9,000 hairs/cm2.
Hair is greatly reduced in most marine mammals
(except sea otters), as it would increase drag.
Marine mammals have thick layers of fat for
insulation.
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Epidermis Glands
Sebaceous glands are associated with hair
follicles and produce oil.
Two types of sudoriferous glands
(1) Small eccrine glands produce sweat, which
functions in evaporative cooling in a few mammals
(2) Large apocrine glands, which can produce
products with a smell.
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Mammary Glands
In humans, many ducts lead from the glands to a
nipple and parts of the duct system are enlarged
to store milk.
Cattle have teats that form by the extension of a
collar of skin around the opening of the mammary
ducts.
Mammary glands are derived from apocrine glands,
and function to provide nourishment for the young.
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Milk
Milk contains water, butterfat, lactose, albumin
and salts. The composition of milk varies with
the species.
In human milk, albumin is low, as well as fat
(roughly 4), resulting in slow growth. In guinea
pigs, high albumin in the milk leads to a
doubling of weight of the offspring every few
days.
The fat content of milk varies, as high as 25 in
sea otters, and 50 in whales
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Teeth
One of the hallmarks of mammalian evolution has
been the development of highly specialized
dentition.
Most mammals do have highly adaptive teeth that
are used in tearing grass, grasping prey or
crushing bones.
Species vary in the number of each type of tooth
and the degree of specialization.
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Teeth
Some mammals (i.e. humans) are omnivorous
feeding on a variety of plant and animal
material. They have anterior teeth with sharp
ripping and piercing surfaces and posterior teeth
with flattened grinding surfaces for rupturing
plant cell walls.
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Teeth
Mammals that eat plant material often have flat,
grinding posterior teeth and have chisel shaped
incisors for nipping or gnawing plant material.
Deer (cow skull looks similar)
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Teeth
Mammals that eat plant material often have flat,
grinding posterior teeth and have chisel shaped
incisors for nipping or gnawing plant material.
In rodents the incisors grow throughout life.
A rodent (beaver)
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Teeth
Canines are typically pointed, and are
particularly important to carnivores. They are
usually long, conspicuous, and have one point.
They are pointed for capturing and killing prey.
Canines are very enlarged in walruses.
A carnivore, the coyote
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Digestive System
The digestive system of mammals is similar to
that of other vertebrates, but has
specializations that reflects their diets.
Ruminants (i.e. cows) have a four-chambered
stomach to allow fermentation of cellulose by
microorganisms.
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Ruminants
Ruminants (animals that chew their cud) have
the most unusual modifications of their stomach.
These animals eat grasses and other vegetation
that has cellulose-based walls. Cellulose
contains a large amount of energy but animals
generally cant digest it.
Gut microorganisms can produce cellulase an
enzyme that can digest cellulose.
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Ruminants
Upper portion expands to form a large pouch the
rumen and a smaller reticulum.
Lower portion contains a small antechamber - the
omasum and the true stomach (abomasum).
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Ruminants
Food first enters the rumen where it encounters
the microorganisms where it is partially digested
(heat and churning help). Pulpy mass moved into
reticulum.
Mouthful regurgitated (cud) and chewed.
Reswallowed food goes back to the rumen where it
becomes more liquid.
Moves into the omasum and abomasum where
digestive enzymes encountered and digestion
continues.
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Temperature Regulation
Mammals are widely distributed and some face
harsh environmental conditions. Most face
temperatures that require them to dissipate heat
at some times and to conserve and generate heat
at other times.
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Temperature Regulation
Mammals may produce heat by (1) shivering
thermogenesis and (2) non-shivering
thermogenesis. The second process involves the
metabolism of special fat deposits called brown
fat.
Heat production is effective in thermoregulation
because mammals can conserve heat several
different ways (1) insulated by hair and/or fat
deposits and (2) with the use of heat exchangers.
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Heat conservation
Countercurrent heat exchangers conserve heat in
animals adapted to cold environments.
In the winter lower part of a reindeers leg may
be 10oC while body temperature is 40oC.
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