USING A DICHOTOMOUS KEY TO IDENTIFY SALAMANDERS
Contributed by Lorelei Crerar
Suppose you are out at the Clifton Institute field station in Warrenton and you find a large colorful salamander while walking near a pond. Chances are the salamander has already been named and classified, but how can you learn its identity? As an aid to help others identify unknown organisms, biologists developed keys that help people classify unknown organisms.
These classification keys are called dichotomous keys (the word dichotomous comes from the word dichotomy meaning “two opposite categories”). A dichotomous key presents the user with two opposite statements about some trait of an organism. By choosing one of the two statements that best describes the unknown organism, the user is lead to further pairs of statements. By going from one set of statements to another, the name of the organism or its classification group is determined. Use the dichotomous key provided on page two to identify the salamanders in Figure 1.
1. Begin by reading statements 1a and 1b. One of the statements describes the salamander and the other statement does not.
2. Follow the directions for the statement that describes that salamander and continue following the correct statements until you have identified it. Record the scientific and common names of the salamander in the data table below.
3. Repeat step 2 for each of the other salamanders in Figure 1.
Dichotomous Classification Key for Salamanders
1
a. Hind limbs absent Siren intermedia, siren
b. Hind limbs present Go to 2
2
a. External gills present in adults Necturus maculosus, mud puppy
b. External gills absent in adults Go to 3
3
a. Large size; over 7cm long Go to 4
b. Small size; under 7cm long Go to 5
4
a. Body background black, large white spots
irregular in size and shape completely
covering body and tail Ambystoma tigrinum, tiger salamander
b. Body background black, small round white spots
in a row along each side from eye to tip of tail Ambystoma maculatum, spotted
salamander
5
a. Body background black with white spots Go to 6
b. Body background light color with dark spots or lines Go to 7
6
a. Small white spots on a black background in a
row along each side of head to tip of tail Ambystoma jeffersonianum,
Jefferson salamander
b. Small white spots scattered throughout a black
background from head to tip of tail Plethodon glutinosus, slimy salamander
7
a. Large irregular black spots on a
light background extending
from head to tip of tail Ambystoma opacum, marbled salamander
b. No irregular black spots on a light background Go to 8
8
a. Round spots scattered along back and sides
of body, tail flattened like a tadpole Triturus viridescens, newt
b. Without round spots and tail not flattened Go to 9
9
a. Two dark lines bordering a broad light middorsal
stripe with a narrow median dark line extending Eurycea bislineata,
from the head onto the tail two-lined salamander
b. Without two dark lines running the length of the body Go to 10
10
a. A light stripe running the length of the body and
bordered by dark pigment extending downward on the sides Plethodon cinereus,
red-backed salamander
b. A light stripe extending the length of the body,
a marked narrow area at the base of the tail Hemidactylium scutatum,
four-toed salamander
6
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