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VERTEBRATES > Marsupials > Flashcards

Marsupials Flashcards

1
Q

What is the sister group of marsupials?

A
  • Eutheria (placentals)
  • Marsupials and Eutheria = Theria (clade) → sister taxa to monotremes → under mammalia
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2
Q

Unique skeletal features of marsupials

A
  • Epipubic bones
  • (can also be found in monotrmes)
  • Thought to be support and protection of the pouch
  • Recently locomotion is thought to be an adaptation of the bone
  • Not present in thylacia
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3
Q

How do marsupial skulls and jaws differ from other groups ?

A

Skull

  • Large face - small brain case
  • Rest is similar to primitive mammal

Jaw

  • Rear part in turned inward instead of outward
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4
Q

How are marsupial teeth different from other groups?

A
  • More teeth than placental mammals
  • 3 premolars and 4 molars in both upper and lower jaw
  • 4 or more incisors - polyprotodont
  • 2 lower incisors - diprotodont - Exception to the rule (possum etc)
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5
Q

What is the main different between marsupials and other groups?

A
  • The reproductive system

Presence of a pouch (50% of species)

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6
Q

Features of the female reproductive system

A
  • Female : completely doubled
  • Fertilisation will occur via one of the
  • Vaginas
  • At birth both vaginas fuse and create
  • Pseudo birth canal
  • In kangaroos birth canal remains open
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7
Q

Features of the male reproductive system

A
  • Mostly similar to placentals
  • Penis behind the scrotum
  • Some species have a bifurcate (forked) penis (in this case the scrotum is behind penis)
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8
Q

How long is the gestation time of marsupials?

A
  • Short gestation time (8-43 days)
  • Extremely altricial young - 1% of adults body mass
  • Average length of gestation = length of menstrual cycle
  • Some marsupials have a simple form of placenta - gestation period is still very short
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9
Q

how does marsupial body temperature differ from placentals?

A

2.5 degrees lower

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10
Q

What three groups of marsupials are found in the Americas?

Classification

A
  • Didelphimorphia (opossum)
  • Microbiotheria (only one extant species: monetalmente)
  • Paucituberculata (7 species of shrew opossum)
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11
Q

What are the 4 groups of marsupials found in Australia and Australasia?

A

Dasyuromorphia (carnivorous species)
Diprotodontia (largest order - wombats, koalas, kangaroos etc) 155 species
Notoryctemorphia (marsupial moles)
Peramelemorphia (bandicoots.. )

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12
Q

What is the distribution of Marsupials?

A
  • 3 groups are found in the Americas
  • 4 groups are found in Australia/Australasia
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13
Q

What is essential when looking at the classifcation of marsupials?

A

The ankle bone pattern

  • Continuous lower ankle pattern (derived feature)
  • Separate ankle structure (primitive feature)

These features of the ankle bone match to their distribution with one exception: The monetalmente

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14
Q

What is the primitive ankle bone condition?

A
  • Seperate ankle structure
  • Seen in the American groups (except monetalmente)
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15
Q

What is the derived ankle bone feature?

A
  • Continuous ankle structure
  • Seen in the Australasian groups & the monetalmente
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16
Q

What are the names given to the American and Australasian groups of marsupials?

A
  • Ameridelphia
  • Australidelphia
17
Q

How did marsupials get to Australia?

A
  • Widest accepted theory
  • They dispersed from the Americas via Antarctica mainland when everything was connected during the late cretaceous or paleocene
18
Q

What there a single, multiple or continuous disperal of marsupials?

A

Single dispersal event from SA to Australia (through Antarctica)

19
Q

Main characteristics of marsupial reproduction

A
  • Pouch/ Marsupium in 50% of species
  • Paired vaginae transport sperm
  • Birth is via a pseudovaginal canal
  • Two uteri
  • Simple placenta in some cases
20
Q

How is pouch positioned?

A
  • Pouch is either upward or backward facing depending on how animals walks/stands
  • Kangaroos are upward facing because they stand up
21
Q

How can fertilisation be altered?

A
  • Fertilisation can be put on hold if mother has a young already
  • Can pause embryo development until mother is more available to care
22
Q

Newborn marsupial features

A
  • Lack cranial skeletal segments
  • No eye pigments or eyelids
  • Separation of heart ventricles incomplete
  • Strong forelimb locomotion to enable climbing to pouch
  • Developed olfactory - sense where pouch is
  • Mouth and nose/tongue? Well developed to latch onto nipple
23
Q

Benefits of such a short gestation period?

A
  • Much less of an energetic cost
  • No need to protect the embryo from the maternal immune system
  • Less risks for the female (extended pregnancy, large embryo….) - risk of predation (can expel embryo and run away)
  • Flexible reproduction
  • Non seasonal breeding in most marsupials
24
Q

Risks of such a short gestation period?

A
  • Tiny newborn is very underdeveloped - at risk
  • Constrains evolution of marsupial forelimb (due to strong initial development of forelimb)
25
Q

Convergences between marsupials and mammals?

A
  • Possums and lemurs - arboreals
  • Striped possum and aye aye: both have similar elongated finger adaptations
  • Gliding

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