256 Evolution? The Fossils Say YES!
snout than nothosaurs (but still retaining the nasal bones, which are lost in plesiosaurs), but
its palate is more like that of plesiosaurs. The rest of its body is also fairly advanced, with
a fairly long neck, deep body, many extra bones along the belly (gastralia), and limbs that
are intermediate between the unspecialized nothosaur foot and the highly specialized ple-
siosaur paddles, which have dozens of extra finger bones (similar to what happened with
ichthyosaur paddles—see fig. 11.7).
Finally, we leave these two euryapsid groups and look at the third example of large
marine reptiles in the Mesozoic. This group is known as the mosasaurs, and they looked
essentially like gigantic Komodo dragons adapted for swimming—which they were. Mosa-
saurs are members of the family Varanidae, or monitor lizards, which includes not only the
Komodo dragon but also all the Australian goannas of Crocodile Hunter fame. Although not
as highly specialized as plesiosaurs and ichthyosaurs, mosasaurs are completely aquatic,
with long bodies, fully developed flippers, and a vertical fin on the tail. Once again, we have
beautiful transitional forms, known as the aigialosaurs (fig. 11.9) from the middle Creta-
ceous of the Adriatic region. As DeBraga and Carroll (1993) and Carroll (1997:324–325) have
shown, aigialosaurs are perfectly intermediate between mosasaurs and their varanid ances-
tors. The aigialosaurs have at least 42 anatomical characters that make them more advanced
than varanids, most of which are concentrated in the skull region and the semiaquatic limbs
(but otherwise aigialosaurs retain the primitive varanid skeleton). There are another 33 char-
acter transformations between aigialosaurs and the most primitive true mosasaurs, most of
which involve developing flippers, extending the body, and developing a vertical fin on the
tip of the tail. The reader is invited to examine DeBraga and Carroll’s (1993) paper in detail
and see how a nice transitional sequence of fossils can be documented.
Snakes with Legs and Hopping Crocodiles
Snakes are vertebrates and vertebrates are classified as higher animals, whether you
like it or not. I mean you can be a higher animal and still be a snake. This seems to be
a rather peculiar arrangement, to be sure. If you can think of a better, let’s have it. . . .
Snakes in a word, are well worth knowing, unless you’d rather know something else.
In closing, I have a little message which I wish you’d relay to some of those people
who won’t read a snake article because it gives them the jumps: there are no snakes in
Iceland, Ireland, or New Zealand. And no snake articles.
—Will Cuppy, How to Become ExtinctIf ever there were a classic “created kind,” it would have to be the snakes. After all, the
serpent supposedly tempted Eve in the Garden of Eden and was forever condemned to
FIGURE 11.9. A number of transitional snake fossils with vestigial legs and hip bones are known from the
Cretaceous. (A) Eupodophis descouensi, with tiny vestigial hind legs. (B) Detail of the leg bones in the
same specimen. (Photos courtesy M. Caldwell) (C) The complete articulated skeleton of the Cretaceous
snake with legs known as Haasiophis. The large cubes are cork spacers to prevent the fossil from being damaged
when it is turned upside down. (D) Detail of the hip region, showing the vestigial hind limbs. (Photos courtesy
M. Polcyn, Southern Methodist University) (E and F) The transitional fossil Adriosaurus, which had functional
hind limbs but vestigial forelimbs, and a long snake-like body. (After A. Palci and M. W. Caldwell, 2007,
Journal of Vertebrate Paleontology 27:1–7)