Animal Hands Different functions of homologous structures Lesson

Animal Hands
Lesson
Different functions of
homologous structures
Many animals share similar body structures. For instance, your nose, a pig's
snout, and an elephant's trunk can all be called noses. Though these noses
have different functions and appearances, all have a similar location and
structure. Such similar features are called homologous structures.
~
~
homologous
Greek.
= "agreeing"
Open x-ray images 01 through 10.
{ File/Open
.
You may have to close one or two images to open the next one.
{ File/Close
.
Briefly examine each image.
in
~ Windows/NeHt
Image to
view each of the x-rays. See
the Windows IPTechnique
Sheet for tips on working
with several windows open.
These x-rays show the hands of the following animals:
beluga whale
human
hyena
lion
macaque monkey
owl
panda
sea lion
sun bear
zebra
A structure's shape is often related to its function. A hand used for swimming
(a fin) is shaped differently than one used for supporting an animal's weight
as it walks. Likewise, a hand used forflying (awing) is shaped differently than
one used to manipulate objects and use tools.
Examine these x-ray images of animal hands in more detail and compare their
structures. Based on the shape of each hand, figure out its main function and
determine its owner.
~
Enhance the features of the animal hands. You may want to use some
of the following techniques. Refer to the Look-Up Tables and Density
Slicing IPTechnique Sheets for more details.
To use this technique
Hints
•
The size of each x-ray is not
related to the size of the
animal.
•
The heavier an animal is. the
thicker its bones are. This is
do this
adjust brightness and contrast
density slice
drag the brightness BCI and
contrast crx sliders in the Map
window.
Options/Density
Edit/lnuert
invert the image
•
both primates, but macaque
hands
have
more padding for swinging
on tree
branches.
Bird bones are difficult to see
•
very thin and light.
Pandas appear to have five
Slice
enhance image with filters
switch color tables
use Process menu items
adjust color tables
use the
Options/Color
•
a sign that the bones support
weight.
Macaques and humans are
in x-rays
Tables ~
+ tool in the LUT
they are
fingers plus a thumb. This
false thumb is an extension
of one of their wrist bones.
If the image loo.ks worse after enhancing ...
Edit/Undo to undo the last thing you did, or
to Saued to return to the original image.
File/Reuert
because
1. Briefly describe the main features of each hand. Here are some clues:
• Does the hand appear to have individual fingers?
•
• Does the hand show fingernails or claws?
• Are the bones thick compared to their length?
•
• How many joints does each "finger" have?
Pandas use it to strip leaves
from bamboo, their main food
source.
Sun bears are small bears.
This sun bear has a deformed
front paw.
You may want to look at a
picture
of each of these
animals .
• Can you tell the shape of the flesh covering the bones?
o
1996 Anzona Board of Regerns.
Lmlfled
dassroom
repmductlOfl
r'9hls are granted under the notice appearing
earlier
In thiS
worl
. :Animal Hands
45
2. In your table, state the function of each hand.
Functions can include:
flying, swimming, grasping/
manipulating, walking/running.
3. Based on the structure and function of each hand, identify the animal
shown in each x-ray.
Mystery Animal
eJ
. r.
Open Myste •...
y Animal.
Animals that are closely related usually have very similar structures. For
example, all species of birds have wings, even flightless birds. Because of
these similarities, you can figure out what kind of animal a hand belongs to
even if you don't know the exact species.
4. Which of the animals in this activity do you think is most closely related
to the mystery animal? Justify your answer.
Further Exploration
A
• On the sea lion, zebra, and human images, use the
tool to label the
characteristics that helped you identify the hand's function. What are the
main differences between the three hands? What do they all have in
common?
• Based on your observations, describe how you would expect an x-ray of
a bat's wing to appear.
• Research the behavior of one or more of these animals to find out what
other functions their hands serve.
• Examine the images in the 200 Animals folder.
)
46
HIP BIOLOGY 1
......
C
1996
Anzona
Board
of
Regents. limited
dasSfOOOl
reproduction
rights
are granted
under
the
notICe
appeaflng
earher
In thIs work.