260 Evolution? The Fossils Say YES!
suddenly they lunge at their prey and grab it and drag it underwater in their “death roll.”
Thanks to movies like Crocodile Dundee and the TV show Crocodile Hunter with the late Steve
Irwin, we have heard a lot more about crocodiles than any other reptile.
Crocodiles have a tremendously diverse fossil record, with many different forms, from
50-foot-long giants that ate dinosaurs for breakfast, to highly specialized marine crocodiles
with flippers and tail fins, to the deep-jawed “bulldog” crocodilian Sebecus, to the peculiar
fish-eating gavials (figs. 11.10 and 11.11). What is most surprising is that crocodiles didn’t
start out large, heavy, or long-jawed. The earliest crocodiles were nothing like any of their
later descendants or like any of the living species. They were small (about a half a meter to a
meter, or 2–3 feet long), delicate, and long-legged with a relatively short snout and long, thin
tail. In the Triassic, we have delicate creatures like Saltoposuchus. Others, like Gracilisuchus
(fig. 11.10A) were apparently bipedal, walking mainly on their long hind limbs, since their
front limbs were so short. Still others, like Terrestrisuchus (fig. 11.10B), were quadrupedal
but extremely delicate, with long slender legs, and probably were excellent runners. Finally,
by the Early Jurassic we have Protosuchus (fig. 11.10C), whose name means “first crocodile”
FIGURE 11.11. From small lightly built forms like Sphenosuchus and Protosuchus (bottom left), the crocodilians
have radiated into a wide variety of body and skull shapes and ecological niches, including fully marine
crocodiles with flippers and tail fins like the Thalattosuchia, crocodilians with long limbs and deep skulls
like dinosaurs (Sebecosuchia), crocodilians with long narrow snouts (Tethysuchia), and the many differently
shaped relatives of the living Crocodylia (upper right). (Courtesy D. Naish)