Origin of mammals Flashcards

1
Q

What group gave rise to the mammals?

A

Synapsids

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2
Q

Describe the transition from Pelycosaurs to mammals

A
  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
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3
Q

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

A

Separates pulmonary and abdominal cavities
= separates respiration and locomotion

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4
Q

Name some key features of early mammals

A
  • Small, insectivorous
  • Nocturnal & solitary
  • Infant/mother bond strong
  • Large olfactory bulbs
  • Endothermy
  • Lactation & suckling
  • Hair (keratin) - insulation, sensory?
  • Large brains
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5
Q

Describe mammals teeth

A

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

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6
Q

How could diphyodonty evolved?

A

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

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7
Q

How did lactation evolve in mammals?

A
  • 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
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8
Q

What adaptations do mammals have for suckling?

A
  • 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
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9
Q

Name some advantages of lactation

A

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

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10
Q

Describe the mammalian development of facial muscles

A
  • Could be from suckling
  • Facial mucles have evolved for chewing and manipulating food
  • Facial expressions possible in mammals!
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11
Q

What group belongs to the Prototheria?

A

Monotremes
(Platypus, spiny anteater, echidna)

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12
Q

What groups belong to the Theria?

A

Metatheria (marsupials)
Eutheria (placentals)

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13
Q

Compare the gestation times of the metatheria and eutheria

A

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

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14
Q

Give some features of the monotremes

A
  • 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
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