Introduction to Mammals

Question 1

What are the 2 sub-classes of mammals?

Answer 1

• prototheria
• theria

Question 2

Describe prototheria

Answer 2

• one order - monotremata
• egg-laying mammals
• platypus and 4 species on echidnas

Question 3

How are prototherias similar to other mammals?

Answer 3

• warm blooded
• hair
• mammary glands - milk
• single lower jaw bone
• 3 middle ear bones

Question 4

How are prototherias different to other mammals?

Answer 4

• oviparous
• urinary, defectory and reproductive systems open into single cloaca
• presence of male monotreme

Question 5

What are the 2 classes of theria?

Answer 5

• metatheria (marsupials): 7 living orders with abdominal pouch
• eutheria (placental mammals)

Question 6

what are the dental formulas for metatheria and eutheria?

Answer 6

• metatheria: 3/3 4/4 (premolars, molars)
• eutheria: 4/4 3/3 (premolars, molars)

Question 7

What are the characteristics of therian mammals?

Answer 7

• homeothermy
• milk production
• give birth to live young
• middle ear bones
• fur and hair
• general skeletal body plan

Question 8

What is an advantage of therians having fur and hair?

Answer 8

enables mammals to be homeothermic in a range of environments

Question 9

Describe the follicle structure in therians

Answer 9

• keratinous filaments
• bulge - stem cells for most of structure
• hair matrix - differentiation
• dermal papilla - signalling

Question 10

Describe the hair follicle cycle

Answer 10

• anagen -> proliferation of cells by dermal papilla
• catagen -> nutrients cut off, hair dies
• telogen -> rest
• anagen -> stem cells in dermal papilla produce new hair, old hair falls out

Question 11

What are the variations in hair development?

Answer 11

• anagen phase determines length
• difference in body regions and individuals: human arms 30-40 days, human head 2-7 years

Question 12

What are some pathologies in hair development?

Answer 12

• extreme stress can trigger rapid progression to telogen
• telogon effluvium - hair spends 30% in telogen, normally 10-14
• alopecia areata - immune attack of follicle

Question 13

What is fur/hair phenotype influenced by?

Answer 13

• density of hair fibres
• follicle shape
• secretions: triglycerides, wax esters, squalene cholesterol

Question 14

Which muscles raise/lower hair in response to temperature?

Answer 14

arrector pili muscles

Question 15

What are the fur/hair types?

Answer 15

• guard hair
• down hair / undercoat

Question 16

Describe guard hair

Answer 16

• straighter, longer
• sensing, protection, camoflauge function

Question 17

Describe down hair / undercoat

Answer 17

• wavier, shorter
• insulation function

Question 18

Describe hairless mammals and their advantages/disadvantages

Answer 18

• some aquatic mammals
• some subterranean mammals
• advantage - streamline, less trapped soil
• disadvantage - less stable temp

Question 19

Describe the specialized fur of the sea otter

Answer 19

• densest fur of all mammals
• required for insulation - air trapped in fur reduces heat loss

Question 20

Describe pigmented hair

Answer 20

• aids camoflage, communication, thermoregulation
• melanocytes give coloration
• die with age giving no colour

Question 21

How does pigmented hair aid camoflage?

Answer 21

• colouration matching similar to landscape
• pattern blending similar to habitat pattern - confused prey/predators

Question 22

How does hair pigmentation aid communication?

Answer 22

• environment - diurnal activity, open habitats, more markings
• social functions
• sexual selections, esp in primates
• skunks - species with black and white coats all produce noxious anal secretions
• gazelle - deterrent signals

Question 23

How does hair pigmentation aid thermoregulation

Answer 23

• reflect/absorb sunlight
• interactions between sweat glands, evaporations, capillaries and fur/skin colour