Biology 483 Exam I fall 2008 Name: In the space provided, briefly

Quadrate-Articular Jaw Joint:

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  For full credit, you should indicate that this jaw type is typical of mammalian ancestors. It is NOT accurate to say that this is a key character for identifying reptiles.
  

Monophyly:

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  For full credit, you should indicate that this signifies a group containing a) an ancestor, and b) all of its descendents. People who gave one or the other received partial credit.
  

Posterior Coracoid:

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  Bone found in the pectoral girdle of mammalian ancestors AND monotremes. Some markdown occurred if people said that this bone was lost in modern mammals.
  

Cynodont:

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  Needed to say a bit more than ‘mammalian ancestor’. Cynodonts were advanced therapsids, survived the Permo-Triassic extinction, had many evolved characters (double occipital condyle, expanded dentary, etc.)
  

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  Needed to indicate that this was a triconodont. Also needed to indicate one of the following: had a fossil in its stomach, displayed mosaic evolution, modern pectoral girdle and derived pelvic girdle…,
  

Temporal Fenestra:

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  Needed to indicate that this was diagnostic for synapsids. Also important (but didn’t need all of these), opening for jaw adductors, expanded in late therapsids and greatly expanded in modern mammals, posterior to orbit…
  

Diphyodont:

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  Two generations of teeth (a lot of people mixed this up with ‘diprotodont’… which is a dentition type in many metatherians).
  

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  Displayed a Q/A AND a D/S jaw type. Highlights problems with key character approach.
  
  
  

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  Needed- at minimum- to indicate this this is a clade defined by presence of a temporal fenestra. I took a half point off when people noted that the clade included modern mammals, but didn’t note the defining feature (T.F.).
  

Diastema:

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  Gap between incisors and premolars- seen in rodents and multituberculates (minimum). Important in the evolution of herbivory.
  

2. Name and briefly describe one of the two grade-based approaches to classifying organisms (3 pts.) . What are two significant drawbacks to grade-based approaches (3 pts. each)?

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  The two are: A) Key Character (using one defining feature- like a D/S jaw joint- to determine which organisms or fossils are members of a clade), B) Suite of characters (choosing a number of defining characteristics. Organisms or fossils that show most are considered members of the clade). A few people would say ‘a key character approach used the D/S jaw joint. I gave partial credit… but this doesn’t really explain what a key character approach IS.
  
  
  
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  The drawbacks we talked about in class were: A) traits evolve multiple times (convergent evolution), B) there are transitional forms (like Diarthrognathus), C) clade-based forms don’t necessarily reflect evolutionary history.
  

3. Contrast the state of the temporal region of a (A) captorhinomorh with that of a (B) pelycosaur and that of a (C) modern mammal. (3 pts. each). Be sure to include the jaw adductors and their attachment points.

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  Drawings were generated twice in class and in the review session. The two most common instances of lost points were: A) failing to show the manner in which the adductors extend through the temporal fenestra, and B) failing to note the manner in which the original bony shield (dermal shield) was lost/fused to the expanded brain case between the pelycosaurs and the late therapsids/modern mammals. I was pretty lenient on the diagrams- I know it’s not an art class! (and I’m darn lucky that it’s not)
  

4. For each of the following families, name the order, and one representative genus (1 pts. per order, 1 pt. per genus).

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  No mystery here- either you mastered these or you didn’t. Note, though, that the suffixes are quite consistent- e.g. ‘mata’ or ‘morphia’ at the order level, an ‘es’ or ‘ius’ suffix for many genera. I’m not saying that you shouldn’t memorize the actual names… bur learning the patterns can help.
  

5. List 6 characteristics unique to mammals (12 pts.).

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  Again- a straightforward exercise in memorization (not implying that it’s easy!!). Many people, however, noted features- such as a four-chambered heart, a temporal fenestra, or dorso-ventro flexion- that are not unique to mammals. (They are diagnostic characters… but are seen in some other taxa).
  
  
  

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  Lactogenic
  
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  Mammalian hair (Should indicate that mammalian hair has a unique structure. I won’t require a description of the details- but cuticular scales, a medulla and cortex, and the presence of arrector pili are all diagnostic)
  
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  Sweat and sebaceous glands
  
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  Annucleate red blood cells
  
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  Separate renal artery and vein- no renal portal system
  
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  Muscular diaphragm
  
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  Facial muscles
  
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  Dorsal pallium is expanded in cerebrum
  
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  Presence of rotating atlas/axis complex in vertebral column
  
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  Tympanic bone (derived from angular)
  
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  Three ear ossicles (malleus, incus, stapes, don’t need to list)
  
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  Single pair of bones (dentary) in jaw- involved in jaw joint
  
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  Diphyodont (two generations of teeth at most)
  
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  Multicuspate teeth
  
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  Regionalization of thoracic column
  
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  Epiphyses on limb bones
  
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  Presence of calcaneum
  

6. Myrmecobiidae exhibits what dietary/life style specialization (3 pts.)? List three adaptations typically associated with this (2 pt. each). What is another genus adapted to this diet (1 pts.)?

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  The lifestyle is myrmecophagus. I gave credit for ‘ant eating’ THIS time- but in the future, I’ll ask that you supply the formal name. (E.G.- ‘jumping’ would not be an acceptable substitute for ‘saltatorial’).
  
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  Adaptations include: long, slender dentary, copious, sticky saliva, long (barbed) tongue, forelimbs modified for digging, reduced pinnae (ears)
  
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  In some cases people would mis-identify the lifestyle (mostly saying ‘fossorial’. In these cases, I took points away for the ID, but gave credit if the associated traits were correctly listed.
  
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  The main alternate genus would be Tachyglossus. Some people listed genera from additional lectures- I credited these.
  

7. Consider the Size-Refugium Hypothesis for the evolution of endothermy. What bearing would the discovery of a fossil pelycosaur with respiratory turbinates have on the hypothesis? Your answer should explain the hypothesis (5 pts.) and indicate why such a discovery would refute, support, or have no bearing on the hypothesis (5 pts.).

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  Here are the key points in the S-R hypothesis:
  

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   Early therapsids, because they were large, had high thermal inertia (and thus a low rate of loss of thermal energy)
   
2. 
   Thus, early therapsids were homeotherms, or ‘gigantotherms’,
   
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   Physiological adaptation occurred (internal chemistry, etc.)
   
4. 
   When the evolutionary radiation of dinosaurs occurred, therapsids evolved towards small size
   
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   With loss of size thermal inertia was lost, heat loss increased
   
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   The physiological adaptations for homeothermy resulted in an evolutionary pressure towards animals that could generate and conserve their own heat
   
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   This lead to many of the key adaptations we see in modern mammals
   

Pelycosaurs were LARGE, and existed before the hypothetical evolution of endothermy. Under the S-R hypothesis, there’d have been no impetus for R-turbinates to evolve in a large organism displaying gigantothermy.

1. 
   Microbiotheria is a South American order. (One of three)
   
2. 
   We once thought that metatherians evolved in N. America, then migrated to Australia via S. America and Antarctica.
   
3. 
   Recent findings suggest that Microbiotheria is closely related to diprotodonts (kangaroos, etc.) (just saying ‘an Australian order’ would have been fine).
   
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   So- why is Microbiotheria in S. America? We have to hypothesize two events… 1) a second dispersal from S.America to Australia, or 2) a dispersal from Australia back to S. America.
   

9. The term ‘primitive’ is often applied to monotremes. In reality, monotremes feature a range of ‘primitive’ and highly evolved characteristics. What is the formal name for varying levels of evolutionary sophistication in an organism? (3 pts.) Draw from the example of Ornithorhynchus, giving two examples of ‘primitive features’ and two examples of ‘evolved’ features in this taxon. (2 pts. each).

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  Everyone seemed to know that we were talking about a platypus (I’d rather marry a duck-billed platypus than end up like old Oedipus Rex… thank you Tom Lehr!!)
  
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  The term is ‘mosaic evolution’.
  
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  Primitive characters include: Cloaca, Pre-post frontal bones, no lacrimal bones, primitive pectoral girdle (with interclavicles, anterior/posterior coracoids, free cervical ribs, epipubic bones, oviparous, large amount of yolk in egg, no nipples, no scrotum- tested in abdominal cavity, no seminal vesicles.
  
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  Evolved characters include: Leathery bill, horny rasping pads (no teeth) in adults, venom, venomous spur, electro and mechanoreceptors.
  
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  A few people listed ‘evolved’ traits that are general to mammals (e.g. lactogenic). I didn’t take points off, although this isn’t really what I was looking for. (I guess the question needed to be more explicit).
  

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  Triumph, the insult comic dog (from Conan O’Brien). I used to work night shifts at a center for disturbed kids… this sketch was gut-churningly funny!
  
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  I gave one point for almost anything that showed a little creativity- two points for ‘Triumph’, insult dog, or the like.
  
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  I tried REALLY hard to find a link to a youtube video that I felt comfortable giving out a link to… no luck. Definitely off-color humor… but check out the skits at the Westminster Dog show or the Republican National Convention if you don’t mind that sort of thing…