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Life of Earth 2 > Chondrichthyes > Flashcards

Chondrichthyes Flashcards

1
Q

What are the 5 features that unite chordates?

A 
>notochord
>postanal tail
>z-shaped muscle segments
>pharyngeal slits
>dorsal hollow nerve chord
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2
Q

What are the features that unite vertebrates?

What about gnathostomes?

A 
>vertebrae
>eye
>cranium
>brain
>tongue
>gill arches

> mineralised teeth
1st gill arch forms jaws
paired fins

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3
Q

Why is a shark’s life cycle unusual?

A

Lay few large eggs w/ big yolks
–>Intensive parental investment

Some sharks e.g. hammerhead:
eggs are retained & hatch internally - fed via placenta or other eggs

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4
Q

How do sharks mate?

A

Have claspers - extensions of pelvic fins

Males fertilise eggs inside the female
= higher chance of fertilisation –> less risk to having just a few offspring

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5
Q

What are shark claspers convergent to?

A

The intromittant organ of amniotes

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6
Q

Describe the hydrodynamics of sharks

A

Large, oily liver helps them float
- but denser than water so must swim to stay up in water column

Don’t have a swim bladder

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7
Q

How do sharks breathe?

A

Ram-breathers
= ventilate gills by forcing water through open mouth

If stop swimming = drown & suffocate

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8
Q

Describe a shark’s skeleton

A

Reduced & cartilaginous
= low density

Lack bone internally
- never evolved bone vertebrae

External bony plates of skull, jaws & body lost - reduced to denticles
= made of enamel + dentine

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9
Q

How do sharks reduce drag?

A

Denticles have parallel giblets
- control production of vortices along body
= reduces drag by 10%

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10
Q

How are sharks specialised for high speeds?

A

Teardrop body
Lunate tail
Elongated fins

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11
Q

Why do sharks replace their teeth every 9-36 days?

A

Fish bones & scales rapidly dull teeth

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12
Q

How are shark jaws highly flexible?

What is so special about Goblin sharks?

A

Jaw cartilage isn’t tightly connected to skull bones

Can protrude jaw to seize prey

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13
Q

What is eyeshine?

What is its importance?

A

When photons pass through retina w/out activating photoreceptors & bounce back

Increases sensitivity of retina to light

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14
Q

What is are the ampullae of lorenzini?

A

Electroreceptors
- detect electric fields

Can home in on prey under seafloor w/out replying on light

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15
Q

How do sharks smell?

A

Each nostril has an incorrect & excurrent opening

Water passes over folds of chemosensitive olfactory tissue

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16
Q

How are sharks specialised for hunting?

A

> specialised jaws & teeth
can hunt in low light conditions
- smell & electrical signals

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17
Q

What are the 3 main cnrondrichthyes groups?

A 
Holocephali = Chimeras
Selachimoprha = Sharks
Rays = Batoidea
18
Q

Give an example of a Holocephali (Chimera)

Describe them

A

Ratfish (aka rabbitfish)

> Toothplates
- incisor like structures to crush prey
Big eyes for darkness
Swim w/ winglike pectoral fins

19
Q

Which era are Chimeras from?

A

Carboniferous

20
Q

What are the features of Batoidea?

A

> flattened body
-glide over seafloor
large pectoral fins extend onto head
pavement of small teeth to crush invertebrates

21
Q

Give examples of Batoidea

A 
Sawfish 
Torpedos
Skates
Stingray
Manta
22
Q

What are the features of sawfish?

A

Long nose w/ spines
= modified denticles
(- NOT teeth)
to club & stun/kill fish

23
Q

What are the features of torpedos?

A

Modified muscle cells discharge an electric pulse

- stuns predator/prey

24
Q

What are the features of skates?

A

Instead of swimming they walk using finger-like projections of pelvic fins

25
Q

What are the features of stingray?

A

Tail spine modified into a long, serrated barb used for defence

26
Q

What are the features of manta?

A

Scoops on the mouth funnel food into mouth

filter feeders

27
Q

What do fossils show about Batoids?

A

Evolved in the Mezosoic

28
Q

What are the 2 main groups of sharks?

A

Squalimorphii (Dogfish, lantern sharks & cookie cutter sharks)

Galeomorphii (requiem sharks, mackerel sharks, catsharks)

29
Q

What are the features of lantern sharks?

A

Photophores on underside
- eliminates silhouette when seen against light coming from above
= camouflage

30
Q

What are the features of cookie cutter sharks?

A

Small dogfish w/ v large teeth that gouge out hemispherical chunk of prey’s flesh

Prey on larger animals (unusual)

31
Q

What are the features of horn sharks?

A

Button-shaped teeth to crush molluscs & crustaceans

Egg-case is spiral-shaped to screw into sediment

32
Q

What are the features of whale sharks?

A

Not predators

  • filter feeders
  • occupied this niche 10s of millions of years before whales
33
Q

What are the features of goblin sharks?

A

Swims or drifts until detects prey w/ electroreceptive snout & shoots jaws out to capture

34
Q

What are the features of thresher sharks?

A

Elongated upper lobe of tail

- used as a whip to stun fish

35
Q

What are the features of mackerel sharks?

A

Can raise body temp well above surrounding water
= endothermic
- lets them maintain high activity levels even in cool water

36
Q

Who do white sharks prey on & why?

A

Marine mammals w/ rich fat reserves

To maintain high activity in cold water

37
Q

When is the oldest shark relative thought to be from?

A

Devonian

- has cartilage skeleton & lacks bone

38
Q

Which group is now recognised as shark relatives?

A

Acanthodians

  • have forsal fin spines
  • scales resemble denticles
39
Q

What do Placoderms suggest about sharks?

A

They has large bony plates on the skull
- suggests ancestor of sharks had extensive body armour

  • reduced in sharks & scales reduced to denticles
40
Q

How has the speed of shark evolution changed since early in their history?

Why has it changed?

A

Rapid evolution early on
–> slows dramatically

Shark design is as good as it’ll get

41
Q

Some sharks have evolved to be filter feeders. What does this suggest about evolution?

A

Things evolve slowly due to competitors prevent them from expanding into new niches

Once competitors are removed evolution speeds up again

Life of Earth 2 (20 decks)

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