early jawed vertebrates

Question 1

what are gnathostomes? when do they date back to?

Answer 1

• Vertebrates with jaws
• Origin- greek
○ Gnathos = jaw
○ Stoma = mouth
• Good fossil record to the mid-silurian (approx. 430 mya) - bc. Of bony material
Previous chordates would try to “suck” in their prey/food - emergence of jaws is a game changer

Question 2

what two structural advancements are game changing about gnathostomes?

Answer 2

jaws and paired appendages

Question 3

what is the greatest advancement in vertebrates? is it in the fossil record?

Answer 3

1. Jaws
   • “greatest advancement in vertebrates” - Alfred Romer
   • Appear in fossil record fully formed
   • Fossils include hyoid apparatus supporting jaws

Question 4

describe the anatomy and importance of paired appendages. what will they eventually give rise to?

Answer 4

2. Paired pectoral and pelvic fins (paired appendages)
   • Very significant - for motion
   • Supported by cartilaginous rays and collagen- connects them to motile structure (the rays)
   • Pectoral and pelvic girdles
   Eventually would give rise to the fore and hind limbs

Question 5

list the nine derived traits of gnathostomes

Answer 5

1. Jaws - from mandibular gill arch
   
   2. Jointed branchial arches - allowance
   3. Hypobranchial musculature - help motility
   4. Two olfactory tracts leading to two nostrils- sensory, protection of chemicals
   5. 1st gill slit squeezed to form spiracle
   6. Three semicircular canals
   7. Conus arteriosus
   8. Horizontal septum
   9. Vertebrae with centra and ribs

Question 6

what were jaws derived from?

Answer 6

mandibular arch (1st branchial arch) - lower jaw

Question 7

what is the purpose of joined branchial arches?

Answer 7

• Give increased flexibility and robustness

Question 8

what is the purpose of the hypobranchial musculature?

Answer 8

suction, inhalation

Question 9

what does the olafactory tract do?

Answer 9

leads to two nostrils

Question 10

what is the spiracle derived from?

Answer 10

1st gill slit.

Question 11

what does the hyoid arch derive from?

Answer 11

seconf branchial arch

Question 12

what is the conus arteriosus? purpose?

Answer 12

small chamber in front of ventricle

dampening strong ventricular pressure

Question 13

what derived feature affected the ears? which one was added?

Answer 13

6. Three semicircular canals - addition of horizontal

Question 14

what does the horizontal septum separate?

Answer 14

Horizontal septum - epaxial and hypaxial units

Question 15

what does the vertebrae with centra protect?

Answer 15

9. Vertebrae with centra around notochord and ribs