Tetrapod Origins

Question 1

Describe Osteichthyans

Answer 1

• bony fishes
• have bony gill cover - operculum
• lung or swim bladder
• endochondral bone

Question 2

What are chondrocytes?

Answer 2

cartilage secreting cells

Question 3

Describe endochondral ossification

Answer 3

• formation of bone inside cartilage
• cartilaginous matrix at first - in embryo
• ossification of cartilage
• invasion by bone secreting cells of modifying cartilaginous tissue leads to ossification

Question 4

Describe the invasion of modifying cartilaginous tissue by bone secreting cells

5 points

Answer 4

• 1st centre chondrocytes
• 2nd centre in growth plates longitudinally
• in adult bone: growth cartilage on epiphysis
• adult bone decreases, growth plates decreaces
• occurs in child/adolescent growth

Question 5

Describe the epiphysis

Answer 5

surface of bones where they articulate from 1 to another

Question 6

Describe the evolution of ossification genes in Osteichthyes

Answer 6

• chimera genome lacks SCPP gene family
• thought it is formed from duplication from ancestral gene

Question 7

Describe the SCPP gene

Answer 7

• ossification of cartilage matrix - Ca2+ binding proteins
• secretory calcium binding phosphoprotein
• gene family

Question 8

What is important in formation of extracellular matrix?

Answer 8

Secreted Protein Acidic Enriched Cystine

Question 9

Describe the evolutionary history of Osteichthyes

Answer 9

sister groups in Osteichthyes:
- Actinopterygii - ray finned fishes that originated with single dorsal fin
- Sarcopterygii - lobe finned fishes

Question 10

Describe polypteriformes

Answer 10

• 12 spp of tropical African freshwaters
• derived dorsal fins - 7 to 18 finlets - example of secondary evolution from single dorsal fin
• relictual characters

Question 11

What are the relictual characters of polypteriformes?

Answer 11

• pair of lungs ventilated via spiracles
• spiral valve intestine

Question 12

Describe Acipenseriform fin structures

Answer 12

• rays of dermal bone fan out from base
• basal elements are endochonral bone
• more derived actinopterygians have less basal elements

Question 13

Describe the swim bladder

Answer 13

• gas filled bladder instead of lungs
• pneumatic duct connects to gut therefore open
• inflated by gulping air at surface
• aids byoyancy

Question 14

Describe respiratory gas bladders in gars and bowfins

Answer 14

• thin wall, air spaces, respiratory epithelium
• allows for air breathing
• gas bladder dorsal to gut
• lungs ventral to gut

Question 15

What is the defining feature of Sarcopterygians?

Answer 15

fin skeleton extending down the limbs

Question 16

What are 3 examples of living sarcopterygians?

Answer 16

• actinistia
• dipnoi
• tetrapoda

Question 17

Describe actinistia

Answer 17

• 2 species of coelacanths
• deep-water marine
• Indian ocean and Indonesia

Question 18

Describe dipnoi

Answer 18

• 6 species of lungfishes - only Australian also has functional gills
• lungs extend from ventral gut as in bichirs
• freshwater

Question 19

What is the genetic program for lungs in Osteichthyes ancestor?

Answer 19

• Tbx4 C-LME control DNA sequence for lungs in mouse embryos
• found in lung-bearing osteichthyes
• lungs ancestral but lost in evolution of actinopterygians

Question 20

What is the oldest evidence of tetrapods walking on land?

Answer 20

• shallow marine tidal flats
• most animals ~2.5m long

Question 21

Describe the fish to tetrapod evolution of neck

Answer 21

• Eusthenopteron opercular bones connect skull to pectoral girdle
• Acanthostega - opercular bones lost, pectoral girdle freed