The arrival of jaws

Question 1

What are Gnathostomata?

Answer 1

A living superclass of Craniata

Question 2

What are 2 ancestors of gnathostomes?

Answer 2

– Thelodonts
– Osteostracomorphs?

Question 3

What are features of Thelodonts?

Answer 3

• Stomachs, unlike extant agnathans
  – Scales like teeth and modern shark placoid scales
  – Broad based pectoral fins

Question 4

What are features of Osteostracomorphs?

Answer 4

– Ossified bones around eye
– Cellular bone
– Slit shaped gill openings
– Paired fin structure
– 2 dorsal fins
– Epicercal tail

Question 5

What is a Heterocercal tail?

Answer 5

A caudal fin composed of two asymmetrical lobes.

Question 6

What is a hypocercal tail?

Answer 6

A tail in which the lower lobe is more pronounced or larger than the upper lobe.
––– Anaspida

Question 7

What is a epicercal tail?

Answer 7

Tail fin in which the the caudal part of the notochord tapers posterodorsally.
–– e.g. Osteostracomorphi

Question 8

What is the order of taxonomic levels?

Answer 8

• Phylum
• Subphylum
  – Superclass
  – Grade
  – Class
  – Subclass
  – Infraclass
  – Division
  – Subdivison
  – Superorder

Question 9

How many classes of Gnathostomata are there?

Answer 9

5

Question 10

What are the living classes of Gnathostomata?

Answer 10

• Chondrichthyes
  – Sarcopterygii
  – Actinopterygii

Question 11

What are the extinct classes of Gnathostomata?

Answer 11

– Placodermi
– Acanthodii

Question 12

What are features of the class Platodermi? X

Answer 12

– Bony, ornamented plates over 30-50% of body
- Big jaws, teeth and large gape: “craniovertebral joint”
- Quite diverse (200 genera)
– Dunkleosteus: 1m x 6m or larger
– Antiarchs: pectoral fins enclosed in bone-like arms

Question 13

What are limitations of Placodermi?

Answer 13

• No replacement dentition
  – Jaw could not generate suction forces

Question 14

What are the defining features of the class Chondrichthyes?

Answer 14

• Prismatic calcification of endoskeletal cartilage
  – Pelvic claspers
  – Specialised as marine predators
  – dominated ancient seaso

Question 15

How many living species of Chondrichthyes are there?

Answer 15

970

Question 16

What are the defining features of the class Acanthodii? X

Answer 16

“spiny sharks”

• Small and stour
• Bony spines before all fins
  – Cartilaginous skeleton
  – Covered in small scales
  – large head and eyes
  – Water column feeders: streamlined, round bodies, reduced armour

Question 17

What are the key features of the class Sarcopterygii?

Answer 17

– Fleshy, lobed fins
– Enamelled teeth
– Cosmic scales

Question 18

How many extant Sarcopterygii are there?

Answer 18

– Only 8 extant fishes
– 26, 742 extant species

Question 19

What are examples of Sarcopterygii?

Answer 19

Australian lungfish, West Indian Ocean Coelacanth

Question 20

How many living species of Actinopterygii are there?

Answer 20

26, 891

Question 21

What are features of Actinopterygii?

Answer 21

– monophyletic but no strong defined characters
– scales: ganoid, cycloid, ctenoid or absent
– spiracle absent
– Gular plate absent

Question 22

What are ganoid scales?

Answer 22

Hard and bony with a shiny surface that resembles enamel.

Actinopterygians

Question 23

What are Placoid scales?

Answer 23

Toothlike, being made of dentine with a pointed backward projection of enamel, as in sharks and rays.

Question 24

What are cosmic scales?

Answer 24

A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales

Question 25

What are cycloid scales?

Answer 25

Round and flexible structures which are present on the surface of bony fishes.

E.g. Actinopterygians – Trout, herring, carp

Question 26

What are ctenoid scales?

Answer 26

Similar to cycloid, except that they have spines or comblike teeth along their free edges; these scales are characteristic of the higher bony fishes—perches and sunfishes, for example.