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.
Mammal-Like Reptiles
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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Skulls and jaws of synapsid reptiles and mammals; left column side view of skull; center column top view of skull; right column side view of lower jaw. Hylonomus modified from Carroll (1964, Figs. 2,6; 1968, Figs. 10-2, 10-5; note that Hylonomus is a protorothyrod, not a synapsid). Archaeothyris modified from Reisz (1972, Fig. 2). Haptodus modified from Currie (1977, Figs, 1a, 1b; 1979, Figs. 5a, 5b). Sphenacodo n modified from Romer & Price (1940, Fig. 4f), Allin (1975, p. 3, Fig. 16);note: Dimetrodon substituted for top view; modified from Romer & Price, 1940, pl. 10. Biarmosuchus modified from Ivakhnenko et al. (1997, pl. 65, Figs. 1a, 1B, 2); Alin & Hopson (1992; Fig. 28.4c); Sigogneau & Tchudinov (1972, Figs. 1, 15). Eoarctops modified from Broom (1932, Fig. 35a); Boonstra (1969, Fig. 18). Pristerognathus modified from Broom (1932, Figs 17a, b,c); Boonstra (1963, Fig. 5d). Procynosuchus modified from Allin & Hopson (1992, Fig. 28.4e); Hopson (1987, Fig. 5c); Brink (1963, Fig. 10a); Kemp (1979, Fig. 1); Allin (1975, p. 3, Fig. 14). Thrinaxodon modified from Allin & Hopson (1992, Fig. 28.4f);Parrington (1946, Fig. 1); Allin (1975, p. 3, Fig. 13). Probainognathus modified from Allin & Hopson (1992, Fig. 28.4g); Romer (1970, Fig. 1); Allin (1975, p. 3, Fig. 12). Morga nucodon modified from Kermack, Mussett, & Rigney (1981, Figs. 95, 99a; 1973, Fig. 7a); Allin (1975, p. 3, Fig. 11). Asioryctes modified from Carroll (1988, Fig. 20-3b). Abbreviations: ag = angular; ar = articular; cp = coronoid process; d = dentary; f = lateral temporal fenestra; j = jugal; mm = attachment site for mammalian jaw muscles; o = eye socket; po = post orbital; q = quadrate; rl = reflected lamina; sq = squamosal; ty = tympanic. .
Are you convinced yet?
Oscillating eye sizes,
head shapes that shift back and forth,
teeth that are large, then small, then large again.
Yeah; I believe this stuff!
(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. )