ulna/radius tibia/fibula

Q: I was wondering how to distinguish the difference between ulna and radius and between tibia and fibula?

A: For our purposes, lets just say the ulna is closer to the higher digits (4 and 5) and it projects to form the elbow protrusion. It is also broader proximally and narrower distally. The radius tends to be smaller and closer to the lower digits (1 and 2). For the hindlimb, just go with the tibia is bigger than the fibula.

determing absolute age by half lives

Q: I was wondering how to determine the absolute age by using half lives. I looked at the
final practice questions and was unable to answer the first five or so questions. The
powerpoint on stratigraphy doesn't really explain how to solve these types of problems
very well. I looked over the slides a few times and am still confused. Thanks.

A: Radioactive decay occurs at a constant rate. As a result, you can use it like a clock. The rate of decay is measured in half lives. The half life of carbon is roughly 5000 years. Carbon-14 decays into Nitrogen-14. Carbon-14 is called the parent isotope, Nitrogen-14, the daughter isotope.

Say you have 16 atoms of carbon 14. After ~5000 years, half of the carbon has decayed away, so there are 8 atoms of carbon 14, 8 atoms of nitrogen. What about after 10,000 years? How many atoms of Carbon 14? (Answer: 4). How many total atoms of N-14? (Answer: 12 = 8 oldones, 4 new ones). After 15,000 years?

A Problem: You have find a fossil snail shell. It has carbon in it, so you can date it using Carbon-14 (C-14) methods. Let’s say you find that you have 15 grams of nitrogen-14 (N-14), and 1 gram of carbon 14. Assume all N-14 that’s there is the result of carbon 14 decay. So, when the snail was alive, it didn’t have any N-14 in it. How old is the snail?

Answer:

OK: how much C 14 was there to start?

15 + 1 grams = 16 grams.

How much carbon is left?

1 out of 16 original grams.

How many half lives is that?

Half-life #1: Carbon goes from 16 -> 8

Half-life #2: 8 -> 4

Half-life #3: 4 -> 2

Half-life #4: 2 -> 1

Four half-lives, each 5000 years: 4x5000 = 20,000 years.

Final Review Question 21

Q: Does a mesotarsal ankle provide us with enough evidence to determine
whether an archosaur with a mesotarsal ankle could be quadrapedal or
bipedal?  Since it's an evolutionary trait for dinosaurs, and some
dinosaurs were quadrapedal and others were bipedal, does that mean a
Marasuchus, who had a mesotarsal ankle, could have been either?

A:  Good Point!  The question relating to this is misleading.  The question is supposed to be about the ankle joint telling us that marasuchus-like archosaurs are very closely related to dinosaurs, and therefore, since marasuchus-like dinos are all bipedal, the first dinosaurs are also thought to be bipedal.   This is also supported by the earliest known saurischians and ornithischians all being bipedal.

UPDATED: 1-2-3 hand and 2-3-4 foot - whose novelties?!

Q:  On the cladograms, a "1-2-3" hand and "2-3-4" foot are evolutionary
traits for dinosaurs but for theropods on the saurischian chart, these
evolutionary traits are also listed for theropods.  Since theropods
are dinosaurs, is it correct to name these traits again?  Is there a
reason they are named again?

A:  There is no good reason!  And it is incorrect since they are supposed to be evolutionary novelties labeled on the cladograms.  They are novelties of dinosaurs, not theropods.  I did talk in lecture about how many of the features of theropods being discussed were not novelties, but they should not have made it onto the cladogram.  Sorry about that!

Q: In regards to the "1-2-3 hand" and "2-3-4 foot" novelty, does that mean there's no real answer to question 41 on the final review?  I am confused however because theropods are known for the loss of the 4-5 finger and 1-5 toe, but since this is a novelty for all dinosaurs, that means it is no longer exclusive to theropods right?

A: OK you caught me again, I jumped the gun saying that the novelty was entirely with the dinosauria rather than the theropoda.  What I should have said was the dinosaur novelties were more asymmetrical hands and feet: reduction of digits 4 and 5 of the hand and digits 1 & 5 of the foot.  Then theropods lose hand digit number 5 entirely, and later tetanurans lose hand digit number 4 entirely.  Foot digit number 1 is severely reduced in theropods and moved to a separate position (and later becomes bigger again in the avian lineages).  Foot digit number 5 is severely reduced and then I believe completely lost in some lineages, but I'm not sure which. 

Thanks for pushing me to get it right! 

Final Review Question 42

Q: I was able to label digit 1 as the one in the back but was unable to figure out what group of theropoda it belonged to.

A: This is a bird since it has a reversed hallux.
See also the post above this about digit numbers.

Final Review Question 26

Q: When you ask coexist, do you mean same area or same time? Because according to your slides, they were alive at the same times but not in the same areas. Wouldn't both of them have met a Tyrannosaurus because both were alive in the Cretaceous?

A: I didn't specifically say this in lecture, but you can be pretty sure that the ankylosaurs would have seen a Tyrannosaur as they were so widespread in the cretaceous. So it must be the stegosaurs and it must be because Tyrannsaurs have not been found in India.

Final Review Question 16

Q: I understand that the pubis is more anterior than the ischium in the pictures. For the second part of the question it asks whether this is always the case and according to the pictures in the textbook it is but I wanted to make sure I wasn't missing anything.

A: Yes, the pubis is always more anterior than the ischium

How do humans share common ancestry with dinosaurs?

Q: Can you please explain question 4 on midterm 2? How do humans share common ancestry with dinosaurs then? Is it just a question of the fact that dinosaurs also were amniotes? Or that they are all vertebrates?
How do we know how far back "common ancestry" means?
Then can humans claim common ancestry with nearly every animal on our cladograms? Because they are all "animals"?

A: YES! We all share a common ancestry, and we can take it back as far as the Last Universal Common Ancestor (LUCA) that all living organisms on earth are thought to share.

Why are "fish" paraphyletic?

Q: Can you please explain question 3 on midterm 2? It asks why fish are a paraphyletic group.
The answer is because they don't include tetrapods, but I don't understand why tetrapods have anything to do with this.

A: To answer this lets look at why fish are not a monophyletic group. Such a group contains an ancestor and ALL of it's decendents. A monophyletic group of "fish" has to include all creatures that descended from fish (and therefore from the common ancestor of all fish). Tetrapods emerged from one type of fish. So if we don't include them in the clade of "fish", then fish are defined as a paraphyletic group (includes an ancestor but not all of its decendents).

Crushed Egg Shells

Q: for the evidence for parental care at nest sites, I don't understand why crushed eggshells is an indicator of parental care, couldn't the eggs be crushed by other critters (since they were laid on the ground) or by natural disasters?

A: good point, but I guess if everything else about the nest is intact (and there are baby dinosaurs in the nest) then it's assumed to be the baby dinosaurs who crushed the egg shells. It shows that these babies were not just hatched when the disaster (whatever it was) quickly buried them.

Who is the closest relative?

Q: ...So closest related is same as asking who shares the more recent common ancestor, but which way do you go on the cladogram-up or down? For example, on lecture 5, slide 75, I don't understand why its the duck when the snail is closer to the fish? And wouldn't the snail be the most recent ancestor?

A: This is a common source of confusion and it's partly because there is some merit to your interpretation, especially when we start saying that certain fish (lungfish) are more closely related to cows than they are to other fish. But, the way cladistics defines relatedness has the advantage of being a clearly defined consistent definition. And it is, as you said, whoever shares the more recent common ancestor. In slide 75, lecture 5, note the time arrow. Any common ancestor higher up on the chart is a more recent common ancestor. To find the common ancestor you go down the cladogram (back in time), and never back up, from each of the taxa until you find a common point. For the fish and the snail that is the bottom of the chart (the first divergence = the oldest divergence = the oldest common ancestor). For the fish and the duck it is the node above, so the fish and the duck share a more recent common ancestor.

Q: what about "sister groups?" Is that the same as a common ancestor?

A: Yes, it's much the same thing. Sister groups share a common ancestor. It's the same as asking "who is the taxon's closest relative. Or, with whom does it share its most recent common ancestor.

I've posted an additional handout related to all this: branchingdiagrams.pdf.

midterm1 question Layers A, B & C

Q: I was wondering if you could explain question 29 on midterm 1 to me.

#29. You're on a dig in Montana and find a fossil in a layer that's on top of a 125 Ma volcanic layer. In Mongolia (very far away) you find three sedimentary layers (A(bottom) ,B, and C(top)), each containing a different type of fossil. The fossil in layer B is the same species as the one you found on the dig in Montana. Which of the below statements is true? It might help you to draw a picture.

I. The fossil in layer A is older than that in B
II. All three fossils are younger than 125 Ma
III. Fossil A is older than 125 Ma
IV. Fossils B and C are younger than 125 Ma

a. I. and III.
b. I and IV
c. III. and IV.
d. I. and II.
e. noodly appendage!

The answer is (b) but if you could explain why "III. Fossil A is older than 125 Ma" is wrong.  Since B and C are younger 125 Ma and layer A is underneath the volcanic layer, then doesn't that make it older?


A:  We know that the layer that has the B-type fossil is less than 125 million years old from the Montana site.  But we don't know how much less... it could be 5 million years old from what we're told.  Additionally, we know that layer A is older than layer B, but we don't know how much older.  So all we can say is that fossil A is older than fossil B, but that could still be much younger than 125 million years.

Review materials for the final?

Q: will you be posting practice questions and/or review material for the final?

A: I will be posting some extra review materials by late saturday.

Curving of exam scores

Q: You said you added five percent to the midterm scores because of the class average being lower than last year (70). Will you update the scores on the my UCLA grades anytime soon, because they are still the same without the curve, or just wait and incorporate the new scores into our final grades? And finally, will you be curving the final as well if the average is below last years?

A: I'm not actually going to add 5 percent to the midterm scores, nor to any scores. Instead the distribution of grades will be such that the average score will be approximately a B- (whatever percentage that is). Please see the distribution in the syllabus to get an idea of how the spread of grades will look. Since the average for that distribution was 75% you can approximate what grade you got for each midterm by adding 5% to your own midterm score and see where that falls on the distribution.

Why is a maniraptor also a tetanuran?

Q: I had a question regarding the cladograms. I think I am still confused on the way to read them. I don't understand #45 on Exam 2. I thought the answer was "maniraptor" but the answer is all of the above. Can you explain this to me in more depth so I understand why that picture represents all of those.

A: Yes, the question was:
The above dinosaur is a:
a. maniraptor
b. coelurosaur
c. tetanuran
d. all of the above

An analogous question might be:
Your pet kitten is a:
a. cat
b. mammal
c. animal
d. all of the above.

all cats are also mammals = all maniraptors are also coelurosaurs.
not all mammals are cats = not all coelurosaurs are maniraptors.
Some mammals are dogs = some coelurosaurs are tyrannosaurs.

You should go through the introductory slides on cladograms and make sure you understand all this. If you are still not sure, you MUST come and see me or your TA! :) We can help explain it.

Identifying flight feathers

Q:  I can't really figure out the difference between a flight feather and a body feather - I know that a flight feather has asymmetric vanes but it looks like
body feathers are asymmetrical as well.

A: Do you remember seeing these feathers in the flight lab?  One was clearly much more asymmetrical than the other.  I suggest you look at the 4th picture down on this page (http://www.earthlife.net/birds/feathers.html) which shows a flight feather(labeled remige) next to a body feather (labeled retrice).  The body feather may be slightly asymmetrical, but in most cases there is no doubt about the flight feather's asymmetry.

Is cauditpteryx an oviraptor

Q: I was wondering whether caudipteryx was an oviraptor or an early branch of the coelurosaurs. On slide 66 in lecture 17, caudipteryx is drawn in before tyrannosaurids but in lecture notes 17, it says that caudipteryx is an oviraptor, which would put it in the dromosaur branch right?

A: Good catch! Yes caudipteryx even moves around the tree within that one lecture! Theropod phylogeny is highly debated and as new evidence emerges there are often changes. For caudipteryx there are two levels of confusion. It was originally proposed to be part of a sister group to the birds, but was later widely recognized to be an oviraptor. Oviraptors themselves were thought to be ornithomimids but are now placed within the maniraptor clade. My apologies for not having that updated in the birds lecture. Although, I would not test on this of course and it does give you a taste of the ephemeral reality of some parts of the tree.

Q: on the note about caudipteryx, I was wondering if you could further clarify something for me - I was studying by looking at the cladogram for feather evolution and so am now wondering whether caudipteryx is still seen as an example of stage 2-4 evolution of feathers. If they're placed in the maniraptor clade, then does that mean that the stage 2-4 evolution of feathers came after the ornithomimid clade and so around the same time as the evolution of stage 5 feathers?

A: Another great question! The phylogeny (branching order) within the maniraptors is unclear but I think there are a few reasons to believe that on the way up to birds, the lineage leading to caudipteryx branched off before the lineage leading to microraptor, and so the argument still holds. The fact that the theropod phylogeny is so uncertain, especially for the feathered dinosaurs, is admittedly a weakness of the claims for the specific stages of feather evolution.

Do we need to know the different birds?

Q: Question about the final. Do we have to know the different types of birds in the cladogram and their differences or do we simply need to know that the cladogram (like the saurichian cladogram on the website) ends with aves?

A: Yes, you do need to know the three non-living birds and their evolutionary novelties as presented in lecture... confuciusornis (pygostyle), Hesperonis (carpometacarpus), and the strange mononykus (carpometacarpus but not a pygostyle)

Tips for the Final?

Q;  DO YOU HAVE ANY TIPS FOR THE FINAL. ARE YOU GOING TO EMPHASIZE ON CLADOGRAMS??. I HAVE TO START STUDYING  ^_*. THANKS.

A:  I strongly suggest the following strategy for studying.
 1)  Start by memorizing the cladograms including the branching order and all of the characters listed.  You should fully understand the cladogram, i.e. how it represents the history of the lineages and which groups have which characters, etc.
 2) Go through the lecture material with the cladograms at hand.  Correlate where on the cladogram each animal discussed fits in.  Make sure you understand (not memorize - that won't work) all of the additional concepts that we talked about.  If there are slides or lines in the lecture notes that you don't fully understand, make of note of them and bring them to my or your TAs office hours.
 3) There will probably be one or two questions on the final exam from the additional readings.  If (and only if) you are going for a top score in the class, then you should go over the additional readings (in the ExtraReadings folder at the course website).

What scores get what grades

Q:  I WOULD LIKE TO KNOW WHAT IS THE SCORE THAT I NEED TO GET TO GET AN A IN THE CLASS. I HAVE DONE ALL THE LABS SO FAR. IN THE MIDTERM I GOT 34/50 . IN THE SECOND MIDTERM I GOT 40/50.

A:  I can't tell you exactly what it will take to get an A, but based on the distribution shown in the syllabus (mean for that year was 75%), your grades on midterm 1 and 2 would be approx.  B- and A  (I added 5% to your scores because our average was 5% lower, 70%).  I would say that you would  need to score over 80% on the final to get an A in the class - this assumes the class average for the final exam is 70%.  If the class average is higher, you'll need a higher score of course.  Also it's assumes that you got close to 100% on all of your labs (except for the one which will be dropped).

Walking with Dinosaurs on Exams

Q: I have a quick question about question #25 on the second midterm, which referred to the Walking with Dinosaurs series. My TA is XXXX and not to put blame on him because he is always helpful and provides interesting insights in lab, but he had told us that we would not be tested over anything in the Walking with Dinosaurs series. A couple of times in lab we have had some technical difficulties and either we did not watch a particular episode or we did not make it all of the way through. My answer to question #25 was Allosaurus because I thought in lecture we had discussed that carnosaurs were the largest land carnivores. I wanted to rely on lecture which was more definite than a the video series which XXXX had said would not be on any of our tests. I understand that disputing a single point on the midterm is pretty trivial in the grand scheme of things, but what I really would like to know is if you are going to put any questions based on Walking with Dinosaurs on the final.

A: Yes, I was worried about the wording of that question because there was not supposed to be anything specifically from the movies on the exam. But I went ahead and used it because I did cover this briefly in lecture where I went over the marine reptiles and how big many are, and I'm pretty sure I mentioned they were the largest carnivores ever. I can promise you there will not be anything on the final exam specifically from the movies!

Final Exam Format

Q: I WOULD LIKE TO KNOW IF THE FINAL IS GOING TOBE MULTIPLE CHOICE ONLY. HOW MANY QUESTIONS ARE IN THE FINAL???

A: The final will probably include short answer questions and/or fill-in questions (e.g. one of the big cladograms with blanks to fill in). There will be approximately 100 questions.