Origin of mammals

Question 1

What group gave rise to the mammals?

Answer 1

Synapsids

Question 2

Describe the transition from Pelycosaurs to mammals

Answer 2

1. Pelycosaurs
2. Therapsids
3. Cynodonts (reduction in size, change in limbs, skull, teeth)
4. Mammals
   Overalll, changes indicate a move to a more upright posture, reduced tail and more active endothermy

Question 3

Describe the function of the diaphram and why its important to mammals

Answer 3

Separates pulmonary and abdominal cavities
= separates respiration and locomotion

Question 4

Name some key features of early mammals

Answer 4

• Small, insectivorous
• Nocturnal & solitary
• Infant/mother bond strong
• Large olfactory bulbs
• Endothermy
• Lactation & suckling
• Hair (keratin) - insulation, sensory?
• Large brains

Question 5

Describe mammals teeth

Answer 5

Most mammals are diphyodont (2 sets of teeth, come in when jaw is fully formed)

Precise occlusion (teeth fit together to fill all gaps)
Not possible in polydont (reptiles, non-mammals synapsids)
So, diphyodont preceded precise occlusion

Question 6

How could diphyodonty evolved?

Answer 6

Through lactation:
- Animal fed milk early in life so didn’t need permanent teeth until later in life (once jaw fully formed)
- So, lactation must have evolved first

Question 7

How did lactation evolve in mammals?

Answer 7

• Mammary glands related to apocrine glands (found in skin)
• Original functions:
  Secreted aggregating pheromones (to bond mother and offspring)
  To protect eggs from desiccation and microbes
• Then evolved as nutritious secretion

Question 8

What adaptations do mammals have for suckling?

Answer 8

• Secondary palate (separation of nasal and oral passages), allows them to feed and breathe simultaneously
• Tight seals in pharynx prevents fluid enetering lungs and stomach in uncontrolled way
• This all allows tounge to manipulate food

Question 9

Name some advantages of lactation

Answer 9

Production of offspring separated from seasonal food supply
Mother not dependent on paternal care
Young born at small body size

Question 10

Describe the mammalian development of facial muscles

Answer 10

• Could be from suckling
• Facial mucles have evolved for chewing and manipulating food
• Facial expressions possible in mammals!

Question 11

What group belongs to the Prototheria?

Answer 11

Monotremes
(Platypus, spiny anteater, echidna)

Question 12

What groups belong to the Theria?

Answer 12

Metatheria (marsupials)
Eutheria (placentals)

Question 13

Compare the gestation times of the metatheria and eutheria

Answer 13

Metatheria (marsupials) → short gestation time, long lactation
Eutheria (placentals) → long gestation, short lactation

Question 14

Give some features of the monotremes

Answer 14

• Egg laying
• Sprawling gait (=swimming/digging)
• No teeth (keratinised pads)
• Bill/beak
• Electroreceptors & mechanoreceptors
• 5 pairs of sex chromosomes
• Obdurodon had teeth → Echidnas & platypus diverged 19-48 MYA