Lecture 21 Flashcards
General Characteristics of Mammals (7)
- Body covered with hair
- Great variety of integumentary glands
- Endothermic
- Dioecious
- Highly developed olfactory sense (smell)
- Highly developed brain
- Most viviparous – placental
• Notable exception: monotremes are oviparous (next lecture)
From Sea to Land
Amniotes are adapted to land
Aquatic mammals May depend partly or entirely on aquatic environment
Mammals
3 groups:
• Monotremes: egg-laying mammals
e.g. platypus
• Marsupials: pouched mammals
e.g. kangaroo, koala, opossums
• Placental mammals
e.g. everything elseIntegumentary System
- Integumentary system:
- Role in protection
- Comprised of skin and appendages
- (e.g. hair, scales, feathers, nails, horns, antlers…)
- Integumentary system distinguishes mammals as a group
Hair uses
• All mammals have hair, and all animals with hair are mammals
Diverse uses for hair • Concealment • Behavioral signaling • Waterproofing • Buoyancy • Thermal insulation
two kinds of hair
• Underhair is soft and dense (for insulation)
• Guard hair is longer and coarse (protection
and coloration)
In aquatic mammals
• underhair is extremely dense and does not get wet
•Guard hair gets wet and forms a protective layer over the underhair
What is hair made of?
- Dead epidermal cells containing keratin
* Keratin is a fibrous structural protein
What is keratin?
• Fibrous structural protein
• Very tough material
• Only found in chordates
• Hair, horns, nails, claws, hooves, scales (reptiles, not fish), shells,
feathers, beaks, quills
• Analagous function to chitin (produced by invertebrates)
What is chitin?
- Nitrogenous polysaccaride
- Very tough material
- Found in arthropods, molluscs, annelids
- Setae of annelids
- Arthropod exoskeleton
- Mollusc radula
- Cephalopod internal shell (e.g. squid beak)
- Fish scales
Shedding in mammals
Most mammals have two annual molts – spring and fall
• Summer coats are thinner than winter coats
• Can be different colour (e.g. white winter coat, brown summer coat)
Examples of modified hairs
- Porcupine quills
* Vibrissae (whiskers) on the snouts of mammals
Horns
- True horns have two parts
- interior bone
- sheath of keratin
- Found in members of family Bovidae
NOT SHED NOT BRANCHED
used for social interactions, competition
Antlers
- Composed of solid bone (no keratin)
- Family Cervidae (moose, deer, caribou)
- Generally, only males produce antlers
- caribou are an exception
- Shed
- Grown in the spring and shed after the breeding season
- Branched
- Used for social interactions, competition for females
Glands
- Great variety of integumentary glands
- Four classes (all associated with the epidermis)
- Sweat
- Scent
- Sebaceous
- Mammary
What is a gland?
An organ or group of cells that secretes a substance that is used or excreted by the body
Sweat Glands
• Occur over much of the body surface in most mammals
Eccrine glands
- evaporates on skin and causes cooling
- water based
- hairless regions in most mammals
Apocrine glands
- milky fluid that dries and forms a film
- Acts in thermoregulation in some mammals and as a pheromone in others
- near puberty regions for humans (armpit breasts groin etc)
- open into hair follicle
Scent glands
- Occur in nearly all mammals
- Used for
- Communication, Marking territory, Warning, Defense
- Most mustelids (skunks, minks, weasels) have scent glands that open by ducts to the anus
- Most odoriferous of all glands
Sebaceous glands
• Usually associated with hair follicles
• Secreted cells expel a greasy mixture called sebum into
hair follicle
• Keeps skin and hair pliable and glossy
• Most mammals have sebaceous glands covering entire body
• In humans they are mostly located on scalp and face
Mammary glands
- Produce milk for young (i.e. lactation) • Occur on all female mammals
- Rudimentary form on male mammals
- In most mammals, milk is secreted from mammary glands via nipples
- Monotremes lack nipples
- milk is secreted onto the fur of the mother’s belly where the young lap it up
Food and Feeding for mammals
Mammals exploit a wide variety of food sources
• Four basic trophic categories • Insectivores
• Carnivores
• Omnivores
• Herbivores
• But many subcategories
• (these four categories don’t adequately describe all mammalian feeding habits)
Trophic = relating to nutrition
Insectivorous Mammals
• Feed on insects and other small invertebrates
• Usually small
• Intestinal tract tends to be short
• eat little fibrous vegetal matter (which
requires prolonged fermentation)
• Teeth with pointed cusps for piercing exoskeleton
• Exception: Anteater - has no teeth, uses tongue
Herbivorous Mammals
Feed on grasses and other vegetation
• Two main groups
• Browsers and grazers :
hooved mammals(e.g.deer, horses, cattle)
Gnawers: many rodents
• Canines are absent or reduced in size
• Molars and premolars are adapted for grinding
- Rodents (e.g. beavers) have chisel-sharp incisors
- Grow throughout life and must be worn away through use
Adaptations for fibrous diet for herbivorous mammals
No vertebrates synthesize cellulose-splitting enzymes .:
- anaerobic bacteria and unicellular eukaryotes produce cellulases in the gut
- These enzymes can break down cellulose via fermentation
• Herbivores generally have long digestive tracts and need to eat
a large quantity of food to survive
Ruminants
• Herbivore Mammals with a large four-chambered stomach
• E.g.cattle,goats,deer,giraffes
• Grass passes down the esophagus to
the rumen
• Digested by microorganisms in rumen
• Ruminant returns cud to its mouth, and ‘re-chews’ it
• Returns to the rumen where it undergoes a second round of fermentation
• Then carries on through “true stomach” (abomasum) where normal digestion occurs
Carnivorous Mammals
Mainly feed on vertebrates, molluscs, crustaceans
• Shearing and piercing teeth, and powerful claws
• Digestive tract is shorter – meat is more easily
digested
• Feed in discrete meals
• More leisure time, but also more active
• Can survive for a long time without food
Omnivorous Mammals
• Use plants and animals for food
• e.g. pigs, raccoons, many rodents, bears,
most primates
• Versatile dentition for a varied diet
• Even some carnivores often will eat fruits, berries, grasses
• Opportunistic
• categories are not always completely clear
Territory
- Many mammals have territories
- areas from which individuals of the same species are excluded
- Mammals mark boundaries of their territories with secretions from scent glands, and with feces or urine
- Territories vary greatly in size depending on size of animal and its feeding habits
- Advantages of a territory
- Interruption-free mating
- Reduce competition for food (particularly when raising young)
- Reduce overcrowding
Three Main Branches of living mammals
• Subclass: Prototheria (Monotremes) • Oviparous mammals
Duck-billed platypus and echidna (that’s it!)
• Subclass: Metatheria (Marsupials)
American opossums Koala, wombats, possums, wallabies and kangaroos
• Infraclass: Eutheria (Placental Mammals)
Many groups!
