ZifanPeng
Name______________________________
Wed 2 co
Section___________________
Earth 7: Dinosaurs
LAB 3: Vertebrate Evolution: Gnathostomes to Archosaurs
In this lab we’ll look at vertebrate evolution from amniotes to ornithodires; in the next lab
we start looking at dinosaurs themselves. It’s important to keep in mind the hierarchical nature of
a cladogram; a particular group possesses its distinctive evolutionary novelties as well as those of
all the more inclusive groups of which it is a member. A crocodile is an archosaur, as well as an
amniote, a tetrapod, a gnathostome, etc. When we ask you to determine what group a particular
animal belongs to, always make sure that your answer is as specific as the diagnostic features
allow. All drawings should include a scale bar indicating the size of the specimen.
1. Here you see three different ganthostomes. In answering the questions below, be as
specific as possible, using the TAXON NAMES on Clagogram 1.
a. To which taxon does specimen A belong?
turtle
finned fish
rag
c. To which taxon
does specimen C belong?
b. To which taxon does specimen B belong?
d. Draw a cladogram illustrating the relationships among these three animals
(and ONLY these three animals).
C
coelacuntnrq
tmtbsynapa.it
2. a. Based on the visible skull characters, to which group do these two animals belong?
b. Sketch one skull and label the evolutionary novelty on which you base your answer.
㲱
1
3. a. These are skin impressions of Lambeosaurus, a duck-billed dinosaur (hadrosaurid).
This kind of skin provides an impermeable (waterproof) barrier. What are the advantages
of having this kind of skin?
good at
b. What group is characterized by this evolutionary novelty?
4. a. Here are the skulls of two “amphibians.” Note the presence or absence of temporal
fenestrae—what is the term for the skull condition possessed by these animals?
swimgsumieinwatanamnanapsid.no
b. Is this skull condition a derived evolutionary novelty that “defines” the amphibians?
Explain why or why not.
buy anysin is
an
stud
coalition
c. Are amphibians monophyletic or paraphyletic? Explain your reasoning.
paraphyletic doesn't include
all descendents
d. “Amphibians” represent some of the earliest diverging lineages of tetrapods. Looking
at cladogram 1, what is the sister group of tetrapods?
longish
5. a. This is an alligator skull. Look behind the eye sockets, along the side and top of the
skull, and note the presence or absence of temporal fenestrae. What is this skull
condition called?
diapi
yes
b. Are alligators archosaurs? _____________________
c. Is the archosaur clade characterized by antorbital fenestrae? ___________________
yes
no
d. Does the alligator have antorbital fenestrae? ____________________
e. Your answers in parts b-d are seemingly inconsistent with expectations. What
accounts for this inconsistency?
Secondary
loss
2
6. a. This specimen is a cast of a juvenile Dimetrodon from West Texas. Based on
information visible on the skull could this specimen be a dinosaur? Why or why not?
b. If not, to what group does it belong?
7. a. The image below shows a dorsal (top) view of a sauropod dinosaur. Below that, please
draw an equivalent dorsal view of the lizard skeleton in from of you, paying close
attention to the features that are visible from above (you don’t need to take too much
time or include lots of detail; a simple stick figure with the appropriate posture will do).
b. Besides the fact that sauropods have longer necks and relatively smaller heads than
lizards, identify the most obvious structural difference between the two animals.
Hint: mammals evolved this character independently of dinosaurs.
8. This is Tylosaurus, a Mesozoic sea dwelling lizard (mosasaur). Is it more closely related
to turtles or archosaurs?
9. Compare the overall body shape of Ichthyosaurus, a Mesozoic sea-dwelling reptile, to
that of a dolphin. The similarity in form between these two animals is due to what type of
evolution?
3