North Seattle Community College's
Instructor:  Tom Braziunas

Weeknumber7.gif (2067 bytes)Questions

Print this for your reference

The reading questions (worth up to 5 points each) for this week are:

1.  In your own words, describe all the evidence that indicates that some ornithopods (especially hadrosaurs) might have spent some time in the water.  Which evidence is most convincing and which is least convincing to you?  Why?

2.  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 battery. 
a> From these photographs and the figures and descriptions in our textbook, explain (in your own words) what a hadrosaur "dental battery" was and 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?
b>  Do you remember (from Chapter 1) how the Iguanodon dinosaur got its name?  Who named it and why? 
c>  Now check out this website 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.
d>  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.  

Royal Tyrrell Museum, Alberta, Canada (Photographs 2007 Tom Braziunas)



Hadrosaur dental battery

Hadrosaur tooth

The following questions relate to visual and audio features in some ornithopods.

a> Explain why many paleontologists  think that the crests and tubes of labeosaurines functioned as both visual and audio signaling devices.
b> Listen to the Parasaurolophus sounds at the following website: (Click on the "Parasaurolophus" link on the left-side list of links).  What modern instrument or noise would you compare this sound to? 
c> What purpose would be served by having the sounds be so low? 
d> Why might the sounds be different for different species? 

4. What features identify a dinosaur as a thyreophoran?  How are stegosaurs distinguished from other dinosaurs?  How are ankylosaurs distinguished from other dinosaurs?

5. 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.

6. 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 ankylosaurids. 
a>  In your own words, what are some of the differences between these two families?
b>  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

7. 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?


The research / thought questions (worth up to 10 points each) for this week are:

8. For the thought questions this week, we return to the world of cladistics to build on our preliminary understanding of cladograms, data matrices and evolutionary novelties 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 these concepts 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 "organisms." 

Let's say that evidence of an amazing new group of organisms has recently emerged -- the "metaworms"!  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 evolutionary interpretation. 

NOTE:  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 evolved 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.). 

The data matrix approach that we practiced before will help us create such a helpful list.  To start systematically building our data matrix, we want to first look for a particular trait or traits shared by all the organisms.  This trait may represent the earliest evolutionary novelty of the group.  Next find a trait that is shared by all the organisms except 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 red X 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 red X 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 developments possible.  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 red Xs.   

Keep in mind the possible "real life" sources of complication.  As one example, convergent evolution 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" data matrix.

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 question below.

Once you have completed your data matrix, provide answers to the following: 
a>  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? 
b>  How many Xs does each of your traits have in its row?
c>  How many Xs 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.

9.   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 diagram" of green boxes within other green boxes to show an alternative way to further visualize what a clade is about.

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 all metaworms.  That is why a red X 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 except 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 of branch M because it is not a member of the "fully or partly segmented body" clade.

The boxes of the Venn Diagram are included to reinforce the idea that clades 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 limbs" clade.  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.  REMEMBER:  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 created. 

a>  Describe your completed cladogram.  What evolutionary novelties fit at 1, 2, 3, 4, 5 and 6? 
b>  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. 

c>  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.
d> 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:   

e> How 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 your ideas.
f> The 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.
g> Finally, 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?

This page was last updated:  04/21/2008 09:21 AM
Number of visits:  Hit Counter