1. John S. Scheibe Nancy D. Moncrief
Geometric morphometric analysis of ecogeographic variation in the eastern fox squirrel (Sciurus niger)
John S. Scheibe
Nancy D. Moncrief

2. Distribution follows hardwood deciduous forests and mixed coniferous forests, with some exceptions

3. Idaho Falls, Idaho

4. Spearfish, South Dakota

5. Sciurus color morph in Florida

6. Size Range of Fox Squirrel
500 g – 1350 g
500 g
1350 g
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7. Weigl 1998 Fox Squirrel Skulls
(size of dot represents skull size)
11 Skull measurements
Adapted from Weigl 1998 VMNH Sp. Pub. 6
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8. Fox Squirrels in southeastern US
eat cones of
Longleaf Pine
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9. Longleaf Pine cones: length = 5 - 12”
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10. larger Fox Squirrels
better adapted
to handle large cones
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11. Fox Squirrel Skeletal Material
used in this study
Indiana
Texas
Georgia
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12. Size Range of Fox Squirrel
Georgia
Texas
500 g
1350 g
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13. Basic Questions
1) Are there shape differences between the 3 populations?
2) If so, is there a corresponding functional difference?
3) If there are functional differences, are they reflective of expected adaptations to diet?
1) It is pretty obvious that the 3 populations differ in overall size. Our interest concerns whether this is a response to some selective regime in the environment. The way to do that I think is by showing that shapes differ in a way that makes sense. Because we expect static allometry regardless of selection, does the allometric pattern match what we think are the functional requirements? So, this brings up question 2) does the shape change also produce a change in function? Our measure here is mechanical advantage of the Masseter. Then, for question 3) does the change in mechanical advantage for the masseter (if it exists) match what we expect for their diets? I would predict a higher mechanical advantage would be associated with at harder diet.
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14. I would like to use this image to orient the audience to the dentary, and talk a bit about landmark placement and why we used the landmarks we did.

15. Representation of the consensus configuration with landmarks and curves. I want to make the point that we really do capture the salient aspects of dentary shape.
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16. Shape Differs Among 3 Localities
So, I will have to introduce geometric morphometrics for a bit. I may insert a slide or 2 to get that idea across. I then want to show that in fact, the 3 populations differ significantly in terms of shape. We know they differ in terms of size, now we know they differ with respect to shape as well.
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17. CV1
I have axagerated the shape differences just a bit for this slide and the next. The turquoise represents the shape on the left side of the previous graph, and the dark blue represents that on the right. So, Texas dentaries are more robust, with a broader base for the incisor and a more procumbent angle for the incisor as well.
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18. CV2
For CV2, the procumbent incisor for Texas is obvious again, Although here the Texas and Georgia dentaries are more gracile relative to Iowa. It is important to note that we are dealing with only a small amount of variation on this axis. Most of the information is located on CV1.
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19. Regression of Size on CV1
So now, we can demonstrate the static allometry. Size and shape are related, and in fact, the texas dentaries have a shape that is significantly different than the larger Georgia and Iowa jaws. I will likely include a slide with the statistical details of this.
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20. Dentary Biomechanics
Now that we know that shape and size are different, what about function? Here I show the biomechanical details. I compute the mechanical advantage for the masseter and the temporalis at the incisor tip, incisor base and molar tooth row.
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21. Area for the masseter increases with dentary size. (R2 =. 90, p <

22. Regressions of Biomechanical Variables on Size
So here is the crux of the biscuit. These are the multiple regression results for biomechanical variables against size. Note first that the variables for the masseter are all significant while those for the temporalis are not. Next, note that the mechanical advantage at the incisor tip and incisor base both decrease with increasing size, but the mechanical advantage for the molar tooth row increases with size. So, while incisor mechanical advantage decreases (together with size) for Texas, it actually increases for the molar tooth row. This suggests to me that Texas fox squirrels are less concerned about opening mast, and more concerned with grinding the food item. Make sense? I need to investigate diets of texas squirrels a bit.
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23. Sciurus breitbartensis