for lessons > Go
back to search results > Lesson
title or topic of activity
Convergent Evolution of Marine Fish and Whales
| The purpose of this activity is
to enlighten young minds about the similarities and differences between
fish and whales. Many of the similarities are a product of convergent
evolution, animals from different lineages that evolve similar morphological
and physiological characteristics because they endure the same environmental
contraints. While explaining the differences, it is important to highlight
the different physiological adaptions to cope with the same conditions.
description or introduction
The scientific principles
that the activity is founded on.
|Although fish and whales come
from different lineages they share many morphological characteristics
as well as some behaviors. When organisms are forced to face the same
abiotic and biotic pressures, some organisms evolve to resemble others
living in the same environment. This concept is known as convergent
evolution. This activity attempts to uncover some of those similarities
as well as differences between fish and whales.
Before jumping into the similarities it is more important at first
to recognize the differences.
|breathe in water with gills
||breathe air with lungs
| lays eggs
||gives live birth
|bony and cartilaginous fish
1) streamlined body shape
2) dorsal and pectoral (flippers) fins. Dorsal fins provide stability.
Pectoral fins and flippers most likely derived from the arms of
3) very efficient gas exchange. Fish utilize a countercurrent system
of gas excxhange where the blood in the gills flow in the opposite
direction to the water. Deoxygenated blood from the body flows opposite
of the oxygenated water producing a more efficient from of gas exchange.
Whales can take in extemely large breaths in a short amount of time.
Compared to humans fin whales take half the time to fill their lungs
with air but a whale breathes in 3,000 times more air. Cetaceans
hold their breath in order to get as much oxygen as they can. As
much as 90% of the oxygen is exchanged during each breath in contrast
to 20% in humans.
4) ability to breathe while feeding. Some cartilaginous fish are
equipped with spiracles located on the top of its snout. These spiracles
take in water for those fish (especially sharks) while it has prey
in its mouth. Remember most sharks need to keep their mouths open
while moving in order to breathe. Whales have blowholes located
near the top of its head. Not only can a whales eat and breathe
at the same time but also take quick breaths while jumping out of
5) strong tail muscles for propulsion. Sharks and tunas have much
red muscles and especially myomeres. These mucles are very strong
and can propel some fish up to 50 miles per hour or more.
6) cryptic coloration and countershading. Skates and Stingrays develop
cryptic coloration to camoflage themselves with the sea floor. Killer
whales are dark with peculiar white patches to breakup its outline
to prey. Both fish and whales utilize countershading as a way to
hide itself in open waters. The dark dorsal side matches the ocean
floor while the light underside blends in with the light shining
7) migration. Schooling fish and certain cetaceans travel through
the same migration routes year after year.
for the activity
time to do the activity
|understand fundamental differences
between fish and whales
|understand how different kinds
of animals can evolve similar features and behaviors because they
endure the same conditions
|understand the different physiological
adaptions that different animals develop
Science Education Standards. (NSES)
content standards that this lesson plan covers:
- A small poster that shows how fish use countercurrent to fully
reoxygenate doxygenated blood.
- A sample of Shark "eggs" to show
- A picture of a whale giving live birth and pointing out it is
born tail first to prevent drowning.
- Show shark teeth and dolphin bones. Ask why there are no shark
- Pictures and diagrams that show the actual shapes of a killer
whale, a baleen whale, a shark and a tuna. Note their steamlined
bodies. Even add that seagulls and seals have also this kind of
body shape. Note the fins and their development from the arms
of land animals (or did they lead into arms?).
- For an activity to prove that fin shape aids in propulsion battery
operated plastic dolphins can be purchased. Break off the tips
of one of the dolphins flippers and have the two race. In theory
the dolphin with the wider fins should come out ahead every time.
Also these dolphins are countershaded. Although not as popular
as they used to be these dolphins can still be purchased through
- Point out countershading in killer whales.
- point out cryptic color for skates or rays.
- A map that shows migration routes of different fish and whales.
Procedure for the Activity
|This activity is for fifth to
eighth graders in groups no larger than eight to keep tham attentive.
work sheets, additional web pages
for discussion or conclusion
|Are their animals that have
deleoped similarities to man because of common environmental restraints
|Can you really say that fish
are more better suited for the ocean than marine mammals?
|Will one day fish invade land?
|Fish and mammals develop differently
form one another. But if you were to put these animals under the same
environmental contraints, after many years of evolution, they may
develop many of the same characteristics.
activities which relate to and extend the complexity of the experiment.
along with a diagram that shows the internal organs of a dolphin.
Here there will be much to compare and contrast.
A web address with information on the topic of the activity.
|Hammer H.M. Predation, Cover,
and Convergent Evolution in Epipelagic Ocean. Marine and Freshwater
Behavior and Physiology 26(2-4) 1995:71-89