Lecture 8

Question 1

What Needed to Evolve During Transition From Water to Land

Answer 1

1. Movement
2. Respiration
3. Sensing the environment
4. Feeding and reproduction
   - Overcoming obstacles related to gravity and air

Question 2

What Structure Defines a Tetrapod:

Answer 2

Vertebrates that possess a Chiridium

Question 3

What is a Chiridium?

Answer 3

Muscular limb with well-defined joints and digits

Question 4

Defining Structures in Early Tetrapods: Tiktaalik

Answer 4

1. Limb-like pectoral fins for support while standing and functional wrist joint
2. Mobile neck allowing flexible head movement
3. No bony gill covering suggesting increased use of lungs for respiration

Question 5

Defining Structures in Early Tetrapods: Acanthostega

Answer 5

1. Limbs have digits (8 fingers and 8 toes)
2. Girdles are designed to bear weight (reinforced pelvic girdle)
3. Tail with fin rays and internal gills suggest it was aquatic

Question 6

Defining Structures in Early Tetrapods: Ichthyostega

Answer 6

1. Limbs have digits (7 fingers and toes)
2. Lacked internal gills

Question 7

Defining Structures in Early Tetrapods: Temnospondyls

Answer 7

1. Gave rise to modern amphibians
2. Semi-aquatic
3. Robust bodies with flat skulls
4. Fossils known from larval stage through metamorphosis

Question 8

Defining Structures in Early Tetrapods: Lepospondyls

Answer 8

1. Occupied specialized niches on land and water
2. Eel/Snake-like forms = aquatic
3. Lizard/Newt-like forms = more terrestrial

Question 9

Seven Major Changes from Fishes to Tetrapods:

Answer 9

1. Fin -> Chiridium
2. Fused Shoulder -> ‘True’ Neck
3. Reinforced Vertebral Column and Girdles
4. Skull Shortening and Lost Hyomandibula Attachment
5. Snout Elongation and Eye Location
6. Reduction of Skull Bone Pattern
7. Integument Modifications

Question 10

1. Transition From Fin to Chridium:

Answer 10

• Elements distal to base of fin expand
• Modified to bear digits in early Tetrapods
• Change in angle between humerus and radius/ulna

Question 11

2. Transition from Fused Shoulder to ‘True’ Neck:

Answer 11

• Loss of bone covering gill chamber (operculum) in fishes
• Loss of bones that joined the shoulder to the back of skull roof in fishes
• Evolution of the atlas vertebra

Question 12

What is the Atlas Vertebra:

Answer 12

First cervical vertebra

Question 13

3. Reinforced Vertebral Column and Girdles

Answer 13

• Centra become more ossified (changes in vertebrae)
• Zygopophyses appear so that the ventral column can help keep the body off the ground (changes in vertebrae)
• Changes in bones supporting the appendages (Changes in girdles)
• Physical connection with a vertebral column for both girdles (Changes in girdles)
• Points of attachment for muscles used in new mode of locomotion (Changes in girdles)

Question 14

4. Skull Shortening and Lost Hyomandibula Attachment

Answer 14

• Back part of the skull is shortened
• Hyomandibula is no longer attached to the otic capsule (‘nose’)
• Hyomandibula becomes stapes (‘ear’)
• Braincase now supported by connection with roof of mouth

Question 15

5. Snout Elongation and Eye Location

Answer 15

Eyes move to the tip of head

Question 16

6. Reduction of Skull Bone Pattern

Answer 16

• Fusion of small bones in the nasal region (anterior)
• Loss of bones in opercular region (posterior)

Question 17

7. Integument Modifications

Answer 17

• Dermal scales of fish were modified into scutes or gastralia
• Cover only the belly in Tetrapods