Week 11 - Vertebrate colonization of land: muscular and skeletal adaptations

Activities

1.  Prelab activity: read Chordate page on Tree of Life page http://tolweb.org/Chordata/2499

2.  Identify the chordate characteristics- synapomorphies.

3.  Find evidence of the common chordate characteristics in humans.

4.  Comparative dissections of perch, frog, and rat to observe descent with modification as evidenced in the musculoskeletal system.

a.  Compare the external morphology of a bony fish, a frog and a rat.

b.  Describe the limb posture of each animal. What part of limb posture is due to adaptations for locomotion (sprawling vs adducted, swimming vs jumping vs walking vs flying)?

c.  Examine the presence or absence of a neck. What are benefits of having a neck when moving on land?

d.  Describe the action of a few select muscles (e.g. flexors vs extensors)

e.  Find evidence of the common chordate characteristics in all dissections.

5.  Thought experiment: how would you test whether a bone you found on the beach belongs to an aquatic or terrestrial animal?

6.  Time permitting: Work on group project.

ACTIVITY 2

List five chordate synapomorphies, characters that unite all chordates and only chordates.

ACTIVITY 3

Because humans are vertebrates and hence also chordates, we should have all the chordate synapomorphies. Hypothesize where in the human body they can be found and how you would recognize them.

ACTIVITY 4

Working in pairs, get one specimen of each of the following: perch, rat and frog. Remove from wrapping and place next to each other on tray.

Observe the animals’ external morphology. Write down one character that is unique to each animal. Based on what you know about the shared vertebrate characters, do you think the unique character you identified is derived, i.e. evolved in this animal lineage, or ancestral, i.e. was present in all vertebrates but lost in later lineages?

Perch / Frog / Rat

Examine the presence or absence of a neck.

Question: What are benefits of having a neck when moving on land?

ACTIVITY 5

Skin one hind limb in frog and rat; skin one side of body in perch. To do this:

Frog: use the scissors to cut along a line at the top of the leg then using the hemostats pull the skin off like a sock, all the way past the toes.

Rat: make a small incision (~1cm) in the loose skin near the tail. Then insert your scissors while closed so that they run under the skin but over the muscles. Keep opening and closing the scissors without cutting to separate the skin from the muscle. When you can’t move the scissors in any further, cut the skin open and proceed until the whole leg muscles are exposed.

Fish: using the scalpel make an incision running along the dorsal edge of the fish body, down the caudal fin, and along the ventral edge of the body. Then using the hemostat pick up the edge of the skin near the tail end and pull the skin parallel to the body so that the muscle below is exposed.

Question: In the fish, what is the arrangement of body muscles like? How does this fish move?

In terrestrial animals with limbs, the action of muscles that move the limbs can be split into 2 categories: adductors move the limbs closer to the body midline while abductors move them away from it. For any muscle acting around a joint, flexors make the angle at a joint smaller, while extensors make the angle bigger.

Find the following muscles on the frog and rat. During your dissection pull on each muscle using your forceps to identify its action. Describe its relative size and its function using the terms above.

Frog Rat

- gastrocnemius

- rectus abdominis

- biceps (rat)/triceps (frog) femoris

Question: Identify one tendon in the frog and rat. What do think is its function?