Well, it has been a while. I have taken some adult re-education classes recently, the most amusing being anthropology where we got to go into the basement storeroom and look at plaster copies of evolutionary skulls and teeth. It would be difficult to put them in proper evolutionary sequence.
As previously stated, a succession of transitional fossils exists that link reptiles (Class Reptilia) and mammals (Class Mammalia). These particular reptiles are classifie as Subclass Synapsida. Presently, this is the best example of th e transformation of one major higher taxon into another. The morphologic changes that took place are well documented by fossils, beginning with animals essentially 100% reptilian and resulting in animals essentially 100% mammalian. Therefore, I have chosen this as the example to summarize in more detail (Table 1, Fig. 1).
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M. Eyes = ?
Nose = ?
Teeth incisors = ?
K. Eyes = ?
Nose = pointy
Teeth incisors = small
J. Eyes = Medium
Nose = stubby
Teeth incisors = BIG
I. Eyes = Medium
Nose = less stubby
Teeth incisors = big
H. Eyes = smaller
Nose = more blunt
Teeth incisors = smaller
G. Eyes = SMALL
Nose = Pointer
Teeth incisors = Skinny
F. Eyes = BIG
Nose = Blunt
Teeth incisors = Thin
E. Eyes = HUGE!
Nose = pointy, again
Teeth incisors = Bigger
D. Eyes = Smaller
Nose = Getting wider
Teeth incisors = Bigger: two!
C. Eyes = Huge, again!
Nose = broader
Teeth incisors = very small
B. Eyes = less huge
Nose = less broad
Teeth incisors = ??
A. Eyes = bigger again
Nose = rounded
Teeth incisors = small
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(The chart is from The Fossil Record: Evolution or "Scientific Creation" by Clifford A. Cuffey. It is on part 5 of a multipart article. The beginning of the article is here. )
I can't believe that.
Some of my fondest memories of grad school are in the bone lab. After you actually look at the bones and casts, and notice the features, it is easy to arrange them in an order. If you use observation and logic, there will be few of the major skulls that are unclear. A lot of the spare parts are more difficult, and folks are using multivariate stats to try to sort them out, but the primary skulls form an awfully clear picture.
Have you actually ever tried this? Great fun!