1. Mammals: Specialized Teeth, Hair, Endothermy and Viviparity
Biology 201 Dr. Edwin DeMont
Chapter 22
Mammals: Specialized Teeth, Hair, Endothermy and Viviparity
Part 1
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2. 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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3. Notable features of mammalian skin are:
Epidermis
Notable features of mammalian skin are:
- Hair (with arrector pili muscle) - Large variety of epidermal glands - Highly stratified epidermis.
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4. 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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5. 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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6. Sebaceous glands are associated with hair follicles and produce oil.
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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7. 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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8. 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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9. 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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10. 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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11. 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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12. In rodents the incisors grow throughout life.
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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13. 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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14. 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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15. 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 can’t digest it.
Gut microorganisms can produce cellulase – an enzyme that can digest cellulose.
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16. 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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17. Ruminants St. Francis Xavier University
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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20. Heat conservation
Countercurrent heat exchangers conserve heat in animals adapted to cold environments.
In the winter lower part of a reindeer’s leg may be 10oC while body temperature is 40oC.
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