Exam 3 - Appendicular Skeleton

Question 1

Fins

Answer 1

Thin membranous process internally supported by dermal fins rays

Question 2

Elasmobranchs fins

Answer 2

ceratotrichia; they are cartilaginous

Question 3

Bony fishes fins

Answer 3

bony lepidotrichia

Question 4

two pterygiophores that support the proximal part of the fin

Answer 4

Basals and Radials

Question 5

Basal pterygiophores

Answer 5

• articulate with the internal girdles

- next to body, large

Question 6

Radial pterygiophores

Answer 6

are thinner and connect the basals to the rays

Question 7

three regions of limbs of tetrapods

Answer 7

• Autopodium
• Zeugopodium
• Stylopodium

Question 8

Autopodium

Answer 8

-Distal portion that includes hand/forelimb (manus) and foot/rear limb (pes)

Question 9

Zeugopodium

Answer 9

• Middle region

- Consists of two bones, tibia and fibula or radius and ulna

Question 10

Stylopodium

Answer 10

• Proximal region

- Single element humerus or femur

Question 11

Gill arch theory

Answer 11

1. Paired fins and girdles arose from the gill arches
2. Accounts for the evolution of girdle but not other elements
   i. Pelvic girdle is displaced too far
   ii. Presence of dermal and not endochondral bone
   iii. Different embryology

Question 12

Fin-Fold theory

Answer 12

1. Arose from a continuous paired set of ventral-lateral folds in the body wall
2. Folds were then stiffened by a transverse series of endoskeletal pterygiophores
3. Composed of the basals and radials
4. Girdle evolution
   i. basals then extended towards the midline
   ii. fused to each other to form the girdles
   iii. this increased the stability of the fins

Question 13

Support for the Fin Fold Theory

Answer 13

i. Early fossil fish contain hints of a lateral fold
ii. Some fossil fish had paired rows of spines in the pelvic girdle
iii. Paired fins of sharks developed from a continuous thickening of the body’s lateral wall

Question 14

Agnathans (fins)

Answer 14

generally lacked paired fins

Question 15

Chondrichthyes (fins)

Answer 15

i. Paired fins are stabilizers and provide anterior lift
ii. Basal portions of the girdles are fused to provide rigidity
iii. Girdles are endochondral

Question 16

Actinoptergygians (fins)

Answer 16

i. Girdles are mostly dermal with some endochondral elements
ii. Hydrofoils are not needed because the air bladder is common
iii. The lateral fins are used for: slow swimming, turning, hovering, and maneuvering
iv. Well developed girdle with multiple elements

Question 17

Sacropterygians

Answer 17

i. Dermal shoulder girdle
iii. Good fossil record of the change
iv. Extant lungfish use their fins to walk on the bottom

Question 18

Eusthenopteron

Answer 18

a. Late Devonian (sarcopterygian)

b. Had limb bones that were homologous with the tetrapods

Question 19

Amphibians (fins)

Answer 19

• quickly displayed adaptations to terrestrial life
  i. Pectoral girdle lost its attachment to the skull
  ii. This enabled an animal to turn its head without turning its body
  iii. It also reduced the jarring of the head during movement

Question 20

Ichthyostega

Answer 20

• early amphibian
  i. Pubis, ishicum and ileum were fused
  ii. Ileum was fused to sacral vertebrae
  iii. Fin rays became digits

Question 21

Pectoral girdle of tetrapods

Answer 21

Dual origin

i. Composed of endochondral and dermal elements
ii. It is not attached to the skull
iii. The number of girdle bones tends to decline across classes

Question 22

Pelvic girdle of tetrapods

Answer 22

i. Composed of three endochondral bones: Ileum, ishium and pubis
ii. Ilium attaches the pelvic girdle to the vertebral column to define the sacral region
iii. Lots of variation in how the three bones are organized

Question 23

the more ______________ force is applied onto the pelvic girdle, the more __________ the pectoral girdle is

Answer 23

compressive; bowl shape

Question 24

Endochondral element of pectoral girdle

Answer 24

i. Fusion or enlargement of basal fin elements

ii. Act as the articular surfaces

Question 25

Dermal component of pectoral girdle

Answer 25

i. Derived from dermal armor
ii. Moved into the fish and joined with the endochondral elements
iii. Functions:
a. Brace the endochondral elements
b. Increase muscle attachment
c. Protect the heart

Question 26

Advantage of lobe fins

Answer 26

1. Crossopterygians had lobe fins
   i. Maybe used to walk on the ocean bottom
   ii. Fins were used as pivot points
   iii. Lateral muscles are flexed to move
   iv. Fins did not have to support the body; the water supported the body
2. Move onto land probably used the same kind of motion

Question 27

Life on land

Answer 27

1. Fin muscles were probably not used in movement or for support in early terrestrial vertebrates
2. They probably fixed the fins to the body like pegs
3. Lateral undulation of the axial muscles caused the body to rotate around pegs
4. Seen in extant lung fish
5. Same body undulations used to swim water work for short distances on land
6. Early amphibians like Ichthyostega were primarily aquatic
7. A fully terrestrial amphibian fauna existed in the Permian period 50 million years after amphibians arose

Question 28

Why leave water?

Answer 28

i. Devonian had an unpredictable climate
ii. Predation in the water
iii. Search for food, mudskippers

Question 29

How do fish swim?

Answer 29

Fish swim by using lateral undulations of the body that overcome frictional and pressure drag

Question 30

Gait

Answer 30

a pattern of footfalls with the substrate during locomotion

Question 31

Diagonal gait

Answer 31

i. Simultaneous placement of diagonally opposite feet on the ground [trot]
ii. Occurs in tetrapods and bottom-walking fishes
iii. Based on the natural undulations of the body
iv. Unstable
v. Not a problem in water because of buoyancy
vi. Dragging the tail or belly
a. Yields greater stability
b. Because you have that triangle, three points of contact
- stability
vii. High frictional drag so energetically expensive

Question 32

Why is diagonal gait unstable?

Answer 32

a. The center of mass is on a thin line between two points of support
b. Body can tip either way

Question 33

Lateral-sequence gait

Answer 33

i. Three of the four limbs are simultaneously in contact with the ground
ii. Triangle of support
a. Center of mass remains within the triangle
b. Animal is never on an edge
iii. Amphibians retain this gait
iv. Less energy expended [unlike where you are dragging the belly or tail]

Question 34

Early modes locomotion

Answer 34

1. Limbs placed laterally
2. Limbs beneath the body
3. Use of pelvic girdle
4. Use of pectoral girdle

Question 35

Limbs placed laterally

Answer 35

i. Locomotion accomplished by alternating lateral undulations of the vertebral column and axial muscles
ii. Still occurs in amphibians and reptiles particularly when they swim

Question 36

Limbs beneath the body

Answer 36

i. Later tetrapods
ii. Rapid locomotion
iii. Crocs can do both
iv. Restricts limb movement to sagittal plane of the body
v. Yields faster recovery from the propulsive strokes and greater efficiency

Question 37

Pelvic girdle as mode of locomotion

Answer 37

i. In therapsids, acetabulum and glenoid fossa shift ventrally to follow the inward shift in body posture
ii. There is a reduction in the adductor muscles
iii. Limbs are underneath the force of locomotion and in the direction of the line of travel
iv. Loss of posterior ribs yield a lumbar region
- Reduces the stiffness and increases flexibility and length of strides

Question 38

Pectoral girdle as mode of locomotion

Answer 38

i. Shift of limbs inward:
a. Moves pressure on the limbs from the distal structures to the scapula
b. Scapula now bears the mass
ii. Force of locomotion no longer to the side of the body but underneath the body
- This form of locomotion works with any gait

Question 39

Cursorial locomotion

Answer 39

A suite of adaptations that lead to high speed locomotion; not all animals have this

Question 40

Speed

Answer 40

of stride length and stride rate

Question 41

What leads to a cursorial lifestyle?

Answer 41

• Prey/ predator arms race or an adaptation for foraging on patchy resources
• Rapid locomotion = are runners

Question 42

Stride length

Answer 42

i. Lengthen the limb

ii. Shift from plantigrade locomotion to digitigrade and unguligrade

Question 43

plantigrade locomotion

Answer 43

which is where the entire foot is in contact with substrate

Question 44

Digitigrade

Answer 44

Walk on the digits

Question 45

Unguligrade

Answer 45

Walk on tip of the toes ex: horses, deer, sheep [hooves]

Question 46

Stride rate

Answer 46

i. Rate at which the limbs are moved
ii. Increase the size of the muscles to move the limb faster
iii. Lighten the distal end to reduce mass and inertia
iv. Takes less energy to move a light limb
v. Reduce the number of digits, lightens the limb and reduces frictional drag