Intro to Mammals

Question 1

What evolved independently in the synapsids and sauropsids?

Answer 1

Endothermy

Fenestra

Question 2

Give a brief evolutionary history of synapsids

Answer 2

Pelycosaurus early synapsid form - large bodied and sprawling limbs

Therapsids more derived - start to get teeth diversification. An example is Dimetrodon

Then Cynodonts - limbs are no longer sprawled to the side but stands upright. Have changes to the teeth

Eventually get mammals

Question 3

What changes happened between early synapsids (Pelycosaur) to mammals?

Answer 3

Posture become upright

Vertebrae become flexible

Reduced tail

Reduction in ribs in the lumbar region - only find ribs in thoracic region)

No ribs leaves space for diaphragm

Become more active and endothermic

Question 4

How do diaphragms work?

Answer 4

It contracts and pulls downwards which increases volume of pulmonary cavity which draws air in

Question 6

What jaw bones became parts of the middle ear?

Answer 6

Quadrate become incus

Hyomandibular becomes stapes

Articulate becomes malleus

Bones used for detection of sound in jaw (possibly vibrations) became incorperated with middle ear

Causes conflict between sense and feeding

Question 7

Give some features of early mammals

Answer 7

Small

Insectivorous

Egg laying

Nocturnal

Solitary

Infant/mother bond strong

Large olfactory bulb

Endothermy

Lactation and suckling

Hair (keratin) - insulation or sensory

Large brains

Question 8

Give some features of lactation?

Answer 8

Feeding young by producing milk

Genes (casein) suggest it only evolved once

Most mammals diphyodont (2 sets of teeth) and have precise occlusion - top teeth fit between in gaps of bottom ones and creates good grinding surface

Lower jaw slightly narrower than upper jaws - allows jaw to move side-to-side

Precise occlusion not possible in polyphyodonty so diphyodonty preceded precise occlusion

Question 9

How could diphyodonty evolve?

Answer 9

Whilst jaw growing - less need of teeth

Animal fed on milk early in life so didnt need permanent teeth until later in life

So lactation must have evolved first

Question 10

How may have lactation evolved?

Answer 10

All females lactate and have mammary glands

Males have rudimentary mammary glands except marsupials and some male bats can lactate

Mammary glands related to apocrine glands (which are associated with hair) so originally secreted pheromones for commumication

Milk may have been produced to protect eggs from desiccation and microbes

Then evolved as nutritious secretion

Monotremes have no nipples

Question 11

What is the evolutionary advantage of lactation?

Answer 11

Production of offspring separated from seasonal food supply - mammals feed when food around and store fat for lactation

Mother not dependent on paternal care

Young born at small body size

Question 12

Give some features of suckling behaviour?

Answer 12

Unique to mammals

Tight seals in pharynx to prevent fluids entering lungs and stomach in incontrollable way:

• seal 1 is at back of tongue and allows for gargling
• seal 2 prevents fluid going down into trachea and allows animals to feed and breathe at same time. lost in human development (only present in babies) which increases choking risk but means we can speak

Question 13

What are the three groups of mammals?

Answer 13

Prototheria (monotremes) - only includes Platypus (Australia) and echidna (New Guinea and Australia)

Metatheria (marsupials) - 70% Australia and 30% Americas

Eutheria (placentals) - worldwide