Dinosaur classification and evolution
This laboratory is designed to help you learn the higher classification of dinosaurs and the
better appreciate the process of evaluating cladistic phylogenies. In preparation for this
lab, you should have read Kritsky chapter 2 and Norman chapter 4.
Write in the appropriate taxon name for the dinosaurs. You will find the answers in your
readings and the slides.
Domain
Kingdom
Phylum
Subphylum
Class
Subclass
Infraclass
Dinosaurs are divided into two superorders. Name them below
Cladistics
Cladistics is the methodology used to develop evolutionary trees based on homologous
structures or shared derived or advanced characters. The procedure is as follows:
1. Determine what primitive characters evolved into derived or advanced states.
Cladistics uses shared derived characters to group dinosaurs in developing an
evolutionary tree.
For this exercise we have identified four derived characters. They are
1.
2.
3.
4.
Five toes evolved into three toes
A body without armor evolved into a body with armor
Walking on two legs (bipedal) evolved into walking on four legs (quadruped)
A hind foot with a wide third metatarsal evolved into an arctometatarsalan hind
foot.
2. Evaluate the different dinosaurs in our study by creating a data matrx and recording if
they possess any of the four derived characteristics. For this lab we will examine the
relationships of three dinosaurs, Tryannosaurus, Ankylosaurus, and Stegosaurus using the
four derived characters listed in step one. For example, Tyrannosaurus has three
functional toes in its hind foot. We will record that derived character by writing a “1” in
the first box under Tryannosaurus.
We know that Stegosaurus has more than three toes in its hind foot, so it possesses the
primitive state, so we will record a “0” in the first box under Stegosaurus in the table.
We will do that for all four of the characters for the three dinosaurs. Upon completion
our data matrix would appear as below.
Derived Character
1. three toes in hind
foot
2. armored body
3. obligate
quadupeds
4. arctometatarsal
hind foot
Tyrannosaurus
1
Stegosaurus
0
Ankylosaurus
0
0
0
1
1
1
1
1
0
0
3. To determine the evolutionary of our three dinosaurs using our four characters
requires that we first draw out every possible evolutionary tree for the three dinosaurs.
There are three possible evolutionary relationships. They are as shown below.
4. To evaluate the three trees we will mark the derived characters from the data matrix
on each tree. We must take care to look for “shared” derived characters. For example, if
both the Tyrannosaurus and Stegosaurus shared the same derived trait, then tree C above
would be marked as below.
The line below the separation denotes that the trait is shared or evolved in Tyrannosaurus
and Stegosaurus from a common ancestor. That fits the definition of homologous
structures. If a Tyrannosaurus had the trait and Stegosaurus did not, then it would be
recorded as shown below.
Finally, a number is placed next to the small line to indicate which trait in our data matrix
is represented by the line.
Completing the process for the four traits on the three possible evolutionary trees would
result in the following:
5. Finally, we can now decide which evolutionary tree (A, B, or C) is the most likely
correct. This is done by using the principle of parsimony or Occam’s razor, which states
that when faced with several explanations, the simplest is the most likely correct. Here
we assume that the tree with the fewest number of convergent evolutions (the same
derived trait independently evolving twice) would be the simplest. Convergent evolution
would be represented on the evolutionary trees by a derived trait number occurring more
than once. For example, in tree B above, derived trait 2 occurs twice and would be an
example of a convergent evolution.
Use the data matix and the evolutionary trees to evaluate the relationships of the three
dinosaurs.
1. The Tyrannosaurus has derived characters
a. 1 and 2
b. 1 and 3
c. 1 and 4
d. 2 and 3
2. The Stegosaurus has derived characters
a. 1 and 2
b. 2 and 3
c. 2 and 4
d. 1 and 3
3. The Ankylosaurus has derived characters
a. 1 and 2
b. 2 and 4
c. 2 and 3
d. 1 and 4
4. The evolutionary tree A has ______ convergences
a. 0
b. 1
c. 2
d. 3
e. 4
5. The evolutionary tree B has ______ convergences
a. 0
b. 1
c. 2
d. 3
e. 4
6. The evolutionary tree C has ______ convergences
a. 0
b. 1
c. 2
d. 3
e. 4
7.
a.
b.
c.
The evolutionary tree that is most likely correct is
A
B
C
8.
a.
b.
c.
d.
e.
The two suborders of dinosaurs are separated by differences in their
number of toes
type of teeth
bones of the pelvis
presence of armor
the shape of their frills
9. Dinosaurs belong to the subclass
A. anapsida
B. diapsida
C. synapsida
E. eurapsida
10. Dinosaurs belong to the infraclass
A. archosauria
B. saurischia
C. ornithschia
D. reptilian
E. eukarya