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2nd Year: Vertebrate Palaeontology > The chordates > Flashcards

Flashcards in The chordates Deck (28)
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1
Q

What 3 main groups does chordata contain?

A
  1. Craniates
  2. Cephalochordates
  3. Urochordates
2
Q

Of the 3 main chordate groups, which 2 are most closely related?

A

Craniata and urochordata.

3
Q

What are 4 major synapomorphies of the chordates?

A
  1. Notochord
  2. Dorsal hollow nerve chord
  3. Myotomes
  4. Pharynx and pharangeal openings
4
Q

What is the neural tube?

A

A structure homologous to the vertebrate spine, it does not expand at the end into a brain.

5
Q

What is the notochord?

A

A stiffened rod of tissue that provides points for muscle attachment in locomotion. Homologous to the vertebral column.

6
Q

What is a common example of a cephalochordate?

A

Amphioxus.

7
Q

Give an example of a urochordate?

A

Sea squirts (tunicates).

8
Q

What is Pikaia?

A

A fish-like organism from the Middle-Cambrian.

9
Q

Why is Pikaia assumed to be the earliest known chordate?

A

It had a notochord and myotomes.

10
Q

Why are the conodonts thought to be a sistergroup to the vertebrates?

A

They have bilateral symmetry, an enlarged brain and eyes.

11
Q

From which group did the vertebrates evolve?

A

Craniata.

12
Q

What are the 2 major groups of extinct agnathostomes?

A
  1. Cephalaspidomorphs

2. Pteraspidomorphs

13
Q

What are the 2 major groups of extant agnathostomes?

A
  1. Hagfish

2. Lampreys

14
Q

What are the 2 major divisions in the cephalaspidomorphs?

A
  1. Anaspids

2. Cephalaspids

15
Q

What kind of tail did anaspids have?

A

Hypocercal tails.

16
Q

What kind of tail did cephalaspids have?

A

Heterocercal tails.

17
Q

What is a hypocercal tail?

A

The tail is weighted/stiffened at the bottom and flexible at the top. This pushes water backwards and up in locomotion, creating lift at the front of the animal.

18
Q

What is a heterocercal tail?

A

The tail is weighted/stiffened at the top and the bottom is flexible. This pushes water backwards and down during locomotion, creating a downward movement. This is counteracted by pectoral fins that create lift at the front of the animal.

19
Q

What 5 features are characteristic of cephalaspids?

A
  1. Dorsoventrally flattened
  2. Large head-shields
  3. Polygonal scales for electrical detection
  4. Evidence of a lateral line system
  5. Fleshy pectoral fins to counteract the heterocercal tail
20
Q

What are 4 major characteristics of pteraspidomorphs?

A
  1. Heavy head armour and chainmail scales at the posterior for flexibility
  2. Hypocercal tail to counteract weight from heavy head armour
  3. No paired fins, presence of spines instead
  4. A single, posterior opening for all gill slits
21
Q

How many species of hagfish are there and what kind of lifestyle do they have?

A

2, scavenging.

22
Q

How many species of lamprey are there and what kind of lifestyle do they have?

A

7, parasitic.

23
Q

What 5 synapomorphies do hagfish and lampreys have?

A
  1. No jaws
  2. No caudal fin
  3. Elongate bodies
  4. No appendages
  5. No true vertebrae (notochord instead)
24
Q

Which group are the extant agnathostomes thought to be descended from?

A

Anaspids.

25
Q

What are 3 major synapomorphies of vertebrates?

A
  1. A centralised nervous system whereby the spinal chord has enlarged at one end to form the brain.
  2. 3 paired sensory organs in the head; optic, olfactory and otic capsules
  3. Development of the vertebrae to form the backbone.
26
Q

The neural tube and notochord in chordates are homologous to which structures in vertebrates?

A

The spinal chord and backbone respectively.

27
Q

From which period of geological time do we begin to see well-preserved vertebrate specimens?

A

The Ordovician.

28
Q

How do agnathostome gills work?

A

By tidal flow.