The reading questions (worth up to 5
points each) for this week are:
In your own words,
describe all the evidence that indicates that some ornithopods
might have spent some time in the water. Which evidence is most
convincing and which is least convincing to you? Why?
Use the photographs below to get a better visual image of the tooth
arrangement developed in hadrosaurs.
The first two photographs show the jaws of two different species of
hadrosaurs. The third photograph is an up-close view of a
hadrosaur jaw that clearly shows its "dental battery." And the
fourth photograph shows an individual hadrosaur tooth which would have
been "locked into" the other teeth in the hadrosaur's full dental
From these photographs and the figures and descriptions in our textbook,
explain (in your own words) what a hadrosaur "dental battery"
how it worked to the advantage of hadrosaurs. How did individual
teeth fit into it? Would you say that the individual tooth shown
in the last photograph is a "fresh" one from within a dental battery or
a "worn" one from the upper layer? Why?
Do you remember (from Chapter 1) how the
dinosaur got its name? Who named it and why?
c> Now check out
on a living iguana
lizard (which is unrelated to the dinosaur, by the way) and compare its
teeth with those of an Iguanodon. Do you agree on the
similarity? Do you also see differences? Explain.
We believe that Iguanodon dinosaurs were herbivores. The
iguana lizard is also a herbivore. That probably means that it
wouldn't be able to use its teeth to defend itself very well against
predators, right? Look over the iguana website again and provide
your opinion as to whether or not an Iguanodon's herbivous teeth
might indeed be effective weapons against predators.
Tyrrell Museum, Alberta, Canada (Photographs
�2007 Tom Braziunas)
Hadrosaur dental battery
3. The following
questions relate to visual and audio features in some ornithopods.
Explain why many paleontologists think that the crests and tubes
of labeosaurines functioned as both visual and audio signaling devices.
Listen to the
Parasaurolophus sounds at the following website:
on the "Parasaurolophus" link on the left-side list of links).
What modern instrument or noise would you compare this sound to?
would be served by having the sounds be so low?
Why might the
sounds be different for different species?
What features identify a dinosaur as a thyreophoran? How
distinguished from other dinosaurs? How are ankylosaurs
distinguished from other dinosaurs?
The brain of a
Stegosaurus has been described (incorrectly) as the size of a
walnut. What was the size of a Stegosaurus
brain? Is this an improvement over a walnut? And, for
comparison, how big was an adult
Stegosaurus? How does this compare to objects in your
house? Was a Stegosaurus larger or smaller
than your car? Explain.
As we know from our
textbook reading assignment this week, the
Ankylosauria are known as the "armored" dinosaurs. The two main
families of Ankylosauria are the nodosaurids and
In your own words, what
are some of the differences between these two families?
Imagine that, on a
visit to the Royal Tyrrell Museum in Alberta, Canada, with your friends,
you point out the two Ankylosauria skulls photographed below. You
explain that one belongs to one of the two Ankylosauria families and the
other one belongs to the other family. You impress your friends
with your analysis of these two skulls. Which skulls belongs to
which families, and what are your reasons for your choices?
Ankylosauria skull #1
Ankylosauria skull #2
Explain in your own
words what defensive strategies were used by ankylosaurs.
What animal(s) today use similar strategies? Do these living
animals look like
ankylosaurs in any of their features?
IN ORDER TO FOCUS
ON THE RESEARCH REPORTS AND TO GIVE EVERYONE A CHANCE TO CATCH UP, WE
WILL NOT WORK ON THE FOLLOWING QUESTIONS. EVERYONE WILL GET CREDIT
The research / thought questions (worth up to 10 points each) for this
For the thought questions this week, we return to the world of
to build on our preliminary understanding of
from our work two weeks ago. As a first step, you may need to
review the meanings of these terms by returning to Chapter 2 and the
homework for Week 5! Then, in order to focus on applying
rather than dealing with unique data tied to specific cases, we will
approach the idea of reconstructing an evolutionary history from a
collection of fossil evidence on a completely imaginary group of
Let's say that
evidence of an amazing new group of organisms has recently emerged --
These creatures have odd-shaped heads and long, cylindrical bodies as
shown in the image below (click on it to enlarge it). I know that
they look a lot like a collection of nails, wood screws, sheet metal
screws, machine screws and bolts (actually they are!) but we will
consider that they are fossils of once living organisms in need of an
I recommend that you click on the
image below to get the expanded view. Then print off the image and
cut it up into its separate boxes. Then you can easily rearrange,
compare, visually play with and try out different groupings of these
metaworm representatives "by hand" rather than just "by eye".
As we learned in our
textbook and our Week 5 homework using the University of California at
Berkeley website on evolution, we will need to decide on which metaworm
characteristics are key "evolutionary novelties" rather than treat
all characteristics equally. Our goal is to try to determine a
possible evolutionary tree (a cladogram) for these organisms. This
cladogram will be our interpretation of which metaworm traits may have
first, second, third, etc.
Our first step is to
closely observe the evidence we have, that is, what are the
characteristics of our organisms that we can see in the data we have
collected. These traits then become our list of potential evolutionary
novelties. We then want to organize these traits into a table
which will help us choose a logical sequence of evolutionary novelties
(which came first, second ,third, etc.).
approach that we
practiced before will help us create such a helpful list.
systematically building our data matrix, we want to first look for a
particular trait or traits shared by
the organisms. This trait may represent the
evolutionary novelty of the group. Next find a trait that is
shared by all the organisms
for one of them. The trait which distinguishes all the other
organisms from this one type of organism (our first "outgroup")
is probably the next evolutionary novelty in the cladogram.
To get us started,
allow me to make a couple decisions for us! The data matrix below
(click on it to enlarge and then print it to work on) already
shows the two traits I have chosen to be the first two evolutionary
novelties in the history of these metaworms:
How did I go about
choosing these traits? Well, all the organisms have a distinct
head at one end of a cylindrical body (so note that all organisms have a
in the data matrix).
Next we can observe that one organism (metaworm A) is the only one with
a smooth body while all other organisms appear to have segments
(threads) partially or fully along their bodies. So we use the
trait of being partially or fully segmented as the next evolutionary
novelty. It is shared by all the organisms except one and so we
hypothesize that it represents the first evolutionary change from the
ancestral smooth body condition. Note then, in the table, that all
organisms are marked with a
except metaworm A.
Now it is your turn!
Observe the additional traits seen in this set or organisms and complete
the data matrix above.
Try to pick the traits which may represent evolutionary novelties that
continue to distinguish smaller and smaller groupings of metaworms.
Make your own decision on the simplest evolutionary sequence of trait
Remember that our goal is to
work out the simplest
evolutionary tree for these organisms BUT that "simple" may not always
be so easy to figure out! You may find that you do not need all
the boxes in the data matrix -- or perhaps you will need to expand the
data matrix to include additional traits. You won't always be able
to separate out just one metaworm that does not fit with the next
smaller grouping of remaining metaworms -- and, as a result, your data
matrix may have a complicated pattern of
Keep in mind the
possible "real life" sources of complication. As one example,
can cause some organisms to look similar but have more distant
evolutionary relationships than it would appear. Also, earlier
traits can seem to "disappear" (that
is, be "lost")
as organisms evolve. So some descendants may be missing an earlier
evolutionary novelty (although we might find evidence for it if we were
able to do a more detailed study of the organism's anatomy). We
will consider these processes more in the next question but, for now, we
should just be aware that we are not looking for a "perfectly logical"
NOTE: A data matrix (and
subsequent cladogram) represents your best assessment of evolutionary
relationships. There are no "right" and "wrong" answers to this
exercise. But you will need to defend your choices in the next
Once you have
completed your data matrix, provide answers to the following:
What are the remaining traits that you used for
evolutionary novelties after the first two that I already listed in the
data matrix? In other words, what traits are in boxes 3, 4, 5, 6,
etc. in your table?
does each of your traits have in its row?
does each metaworm have in its column?
I need to know
enough information so that I can reconstruct your data matrix myself
without actually seeing it.
We now need to take our data matrix information and convert it to our
best visual interpretation of a "family tree" (cladogram)
for the metaworms. A blank cladogram is shown below (which
can be clicked on to enlarge for printing). Above the branches of
the cladogram, I have added a "Venn
green boxes within other green boxes to show an alternative way to
further visualize what a clade
To get started, I will
demonstrate how to start to fill in this cladogram based on the two
evolutionary novelties that I defined in our data matrix for the
metaworms. The first trait, a "cylindrical
body with a head",
is a trait that is found in
metaworms. That is why a
is shown in every column in the data matrix. And that means that
this evolutionary novelty belongs at location "1"
on the cladogram. It is at the base of the family tree for
metaworms. All metaworms on the cladogram have this trait.
All metaworms belong to the
"cylindrical body with head" clade.
And this clade is represented by the
biggest green box
in the Venn Diagram. This box contains all metaworms.
The second evolutionary
novelty on the family tree looks to be the "fully
or partly segmented body"
trait which is found in all metaworms
one. This evolutionary novelty belongs at location "2"
on the cladogram. All metaworms further up the family tree possess
this trait. They all fit into the
second biggest green box in the
Venn Diagram (which is inside the
biggest green box). Only metaworm
A does not have this evolutionary novelty. We place it at the end
because it is not a member
"fully or partly segmented body" clade.
The boxes of the Venn
Diagram are included to reinforce the idea that
are evolutionary groupings within groupings within groupings.
According to the way I have begun building our metaworm cladogram, all
metaworms (A through I) belong to the first clade defined by the
evolutionary novelty at location 1. Moving along the cladogram
tree, we see that metaworms B through I also belong to a second clade
within this primary clade. They possess both evolutionary novelty
1 and evolutionary novelty 2. Only metaworm A is not included in
this second clade -- it lacks evolutionary novelty 2.
In the same way, as we
learned doing the homework for Week 5, you and I are members of the "vertebrate"
clade. Not only are we members of this clade, but we are members
of the "bony skeleton"
clade within it. And within that clade, we are members of the "4
Continuing along our evolutionary tree, we are also members of the "amniotic
egg" clade and,
within it that, we belong to the "hair-possessing"
clade of organisms. Note that it is no longer obvious that we
belong to the "amniotic egg"
clade because that evolutionary novelty has evolved further in mammals,
making our evolutionary heritage more of a challenge to trace back.
In any case,
hopefully, the Venn Diagram visualization is helpful to you. If
not, it does not matter to the construction of the cladogram. Just
ignore the boxes and focus on the
"family tree" (cladogram)
aspect of the sketch. This cladogram rendering is the same as the
sketches throughout the textbook chapters we have been studying.
Now it is your turn again!
Using the data
matrix that you built above, complete the cladogram by filling in where
each metaworm species and evolutionary novelty fits on this sketch.
You may not need all the branches in this generic drawing
of a cladogram in order to illustrate your interpretation of how the
metaworms evolved. More than one metaworm species might need to be
placed at the end of a branch. On the other hand, you may need more
branches, depending on the data matrix you
Describe your completed cladogram.
What evolutionary novelties fit at 1, 2, 3, 4, 5 and 6?
Which metaworms belong at branch tips m,
n, o, p, q and r? Explain your choices.
As pointed out for
the question above, several factors can
further complicate the process of cladistics. For example,
convergent evolution, as our textbook notes, can mislead us into
believing close relationships between organisms which have, in
actuality, independently evolved similar characteristics (like bats and
birds both having evolved wings). In other cases, some organisms
have reversed an evolutionary trend (such as whales being mammals which
have returned to an ocean environment). Sometimes new fossil
evidence is found which causes us to revise or completely rethink the
evolutionary tree we have constructed (which was based on only sketchy
fossil evidence to begin with). Or we may find partial remains of
organisms which make it difficult to determine how they might fit into a
particular evolutionary story.
Are there any
examples of convergent evolution in the way organisms are arranged on
your cladogram? Describe these examples or, if you have no
examples, describe what one would look like.
Are there any examples of
apparently "lost" evolutionary novelties in the way organisms are
arranged on your cladogram? Describe these examples or, if you
have no examples, describe what one would look like.
Say we have found
the fossil remains of three more metaworms as shown in the image
below. New data can be
challenging and also enlightening! Usually we do not "know the
right answer" but can only hypothesize as best we can based on the
available evidence. Let's take on the following three challenges:
does metaworm J fit into your cladogram above? Does it belong on
the same branch as another metaworm type? Or does it
cause you to rethink your cladogram in some way? Please explain
next discovery, metaworm K, is a surprise! It looks a bit
different from any other metaworm we have seen before. How would
this metaworm fit into or change our cladogram? For example, do we
need an additional branch? There may be several possibilities --
please explain the ones you think are most likely and why.
we find a metaworm with parts that are missing (its head, for one!).
We find many dinosaur remains with missing parts so this is a common
occurrence. What do we do with this specimen? What can we
say about it based on the cladogram we have created? Where might
it fit in and what assumptions do we need to make?