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VERTEBRATES > MAMMALS > Flashcards

MAMMALS Flashcards

1
Q

Which group are the mammals derived from?

A

Synapsids

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2
Q

What is a similarity between synapsids and sauropsids?

A

Both evolved endothermy (independently)

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3
Q

What happened to synapsids during the permian-triassic period?

A
  • They were hit badly by the end permian-triassic extiction
  • This reduced the amount of families
  • Mammals and therapsids had relatively small numbers
  • Diapsid reptiles diversified in this time (triassic)
  • Mammals radiated again later (around the time of the dinsosaur extinction)
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4
Q

What caused the mammals to radiate?

A
  • Therapsids died out - gave rise to mammals.
  • Extinction of dinosaurs?
  • Change in vegetations?
  • Not really known but could be a combination of things
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5
Q

Basal synapsid group

A
  • Pelycosaurs
  • Basal group
  • Dimetrodon (form of pelycosaur): Sail on back (thermoregulation)
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6
Q

What were therapsids?

A
  • Early more derived synapsids
  • Had larger bodies
  • Differentiation of teeth
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7
Q

What were Cynodont features?

A
  • Synapsids that gave rise to mammals
  • Reduction in size
  • Change in limb placement - moved under body
  • Changes to skull and teeth
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8
Q

What did the changes in Cynodonts indicate?

A

A move towards endothermy

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9
Q

How did Cynodont limb placement change?

A

Limbs moved under body instead of out to side

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10
Q

Synapsid groups (basal to mammals)

A
  1. Pelycosaur
  2. Therapsid
  3. Cynodont
  4. Mammal
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11
Q

What are the changes in body form of Synapsids from basal to mammals?

A
  • Upright posture
  • Flexible vertebrae
  • Reduced tail
  • Reduction in ribs freed up lumber area and suggests they had a diaphragm
  • Active, endothermy
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12
Q

What specialised feature that is unique to mammals changed their ventilation process?

A
  • The diaphragm
  • Sheet of muscle dividing pulmonary and abdominal cavities
  • Allows unique lung ventilation
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13
Q

What is the name for teeth that are all the same?

A

Homodont

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14
Q

What is the name for teeth that are different/ have different specialisations?

A
  • Heterodont
  • E.g. Molars, incisors, canines etc
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15
Q

What is the name of the main bone in the lower jaw of mammals?

A

Dentary

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16
Q

How is the dentary bone specialised in mammals?

A
  • Other bones got incorporated into the middle ear
  • Before other bones were thought to be part of a hearing mechanism
  • Jaw initially used for hearing and feeding
  • Used bone to detect vibrations
17
Q

How is the joint of the mammal jaw specialised?

A
  • More complex = stronger
  • Early synapsids had weak joint
  • Mammals have developed strong jaw
18
Q

How is the mammal skull modified?

A

Orbit has combined with temporal fenestra

19
Q

What is the zygomatic arch?

A
  • Essentially our cheekbones
  • Arch is well developed
20
Q

How are locomotion and ventilaiton differ between early synapsids (and lizards) and mammals?

A

Lizards and early synapsids

  • Respiration and locomotion linked
    Not very efficient

Mammals

  • Separation of respiration and locomotion
  • Fast movement can aid in the ventilation of the lungs
21
Q

Characteristics of early synapsids

A
  • Small, insectivores
  • Egg laying - amniote condition
  • Nocturnal & solitary - most mammals haven’t got colour vision
  • infant / mother bond strong
  • Large olfactory bulbs - smell was important
22
Q

What are the distinct features of mammals ?

A
  • Endothermy
  • Lactation and suckling
  • Hair (Keratin): insulation, possibly evolved for some kind of sensory function?
  • Large brains
23
Q

What is diphyodont?

A

Two sets of teeth (milk and adult)

24
Q

What is the main theory for why diphyodont evolved?

A
  • Animal fed milk early in life so didn’t need permanent teeth until later
  • So lactation must have evolved first
25
Q

Evidence for lactation

A
  • Most mammals are Diphyodont
  • Also have precise occlusion
  • Precise occlusion not possible in reptiles and early synapsids
  • Diphyodont preceded precise occlusion
26
Q

How many times was lactation thought to have evolved?

A
  • Believed to have evolved once
  • Casein genes are seen in every group of mammals
  • Casein genes are the genes that produce milk
27
Q

What is precise occlusion?

A
  • Teeth fit together precisely
  • Allows for grinding of teeth
  • Interdigitating
28
Q

How do mammals upper and lower jaws fit together and what feeding habits does this allow?

A
  • Lower jaw is smaller than upper
  • Allows movement from side to side (chew food)
29
Q

How did lactation evolve?

A
  • All female mammals lactate and have mammary glands
  • Some males (e.g. some bats) lactate
  • Mammary glands related to apocrine glands (found in skin associated with hair)
  • Originally secreted aggregating pheromones
  • Milk may have been produced to protect eggs from desiccation and microbes
  • Then evolved as nutritious secretion
  • Monotremes have no nipples
30
Q

What is the evolutionary advantage of lactation?

A
  • Production of offspring separated from seasonal food supply
  • Mother not dependent on paternal care
  • Young born at young stage of development
31
Q

What allows suckling?

A

Secondary palate

32
Q

What are the benefits of a secondary palate?

A
  • Tight seals in pharynx → prevents fluids entering lungs and stomach in uncontrolled way
  • Separates nasal and oral passage
  • Allows tongue to manipulate food
33
Q

What is the structure of the secondary palate?

A
  • Hard and soft palate
  • Soft palate creates 2 seals
  • Allows animal to feed and breath at the same time
34
Q

What is the function of seal one in the secondary palate?

A

Allows gargling

35
Q

What is the function of seal two in the secondary palate?

A
  • Forms between soft palate and epiglottis
  • Prevents flow of substances from mouth entering trachea
36
Q

What happened to seal two in human?

Secondary palate

A
  • It is lost in adult humans
  • Prone to choking
37
Q

Example of a type of adaptive feeding habit that the seals of the secondary palate allow?

A
  • Baleen whales use seals for feeding - filter feeding
  • Not possible in any other animals
38
Q

what has the development of the facial muscles allowed in mammals?

A
  • Sauropsids well developed for swallowing - don’t chew
  • Mammals chew so muscles evolved new functions
  • Homologous with neck constrictor muscles of other tetrapods

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