Jawed Fish

Question 1

Jawed vertebrates

Answer 1

Gnathostomata = “jaw + mouth”
- where did the jaws come from?
- why did they evolve?
- why are they one of the biggest vertebrate developments?

Question 2

Origin of Jaws

Answer 2

From “2 pairs” or endochondral cartilaginous articulated arches: mandibular and hyoid arches
- Evo-devo and genetic evidence:
- similar in form, machinery, and origin to gill arches (i.e., supports and pumps water across gills)
- But note the 2 pairs of pseudobranches anterior to these:
- evo-devo evidence: derived from mandibular arch

Question 3

Paired Fins

Answer 3

• Pectoral and pelvic pairs
• yaw, pitch, roll
• Two-part hypothesis origins:
  1. Finfolds (e.g., anaspids) -> row of finlets -> paired fins
  2. Outgrowths of lateral plate mesoderm tissue

Question 4

“Placoderms”: The First Gnathostomes

Answer 4

• The armored fishes with jaws
  
  • Ornamented bony shield
• Separate head and trunk shield (unlike “ostracoderms”)
• Mobile joints (jaws, hinged head/neck, fins)
  
  • head lifted up during feeding

Question 5

“Placoderm” Endo and Exoskeleton

Answer 5

Endoskeleton: cartilage
Exoskeleton: dermal bone
Placoderms were the most common, most diverse of Devonian vertebrates; now extinct