Picture of brachychampsa montana reptile

This alligator ancestor, called an alligatoroid, likely fed on ancient turtles. It looked much the same as its modern-day descendents.

Image © National Geographic Society

Fast Facts

8 to 10 ft (2.5 to 3 m) long
Did you know?
Modern alligators look much the same as their 80-million-year-old ancestors.
Size relative to a 6-ft (2-m) man

Please add a "relative" entry to your dictionary.

This freshwater, carnivorous reptile is among the very earliest alligatoroids known to science. The first Brachychampsa fossil was discovered in Montana's Hell Creek Formation—an ancient suite of rocks that was laid down near the end of the Cretaceous period. That individual animal lived not so long before the Cretaceous-Tertiary extinction that wiped out many of Earth's species some 65 million years ago.

Brachychampsa had short teeth and a large mouth that packed more power than those of living gators. These oral characteristics suggest that Brachychampsa may have preyed on turtles, which were very common in the Hell Creek fauna.

The first alligator ancestors evolved some 245 million years ago. About 80 million years ago, during the Cretaceous period, crocodilians appeared. This group includes alligatoroids, such as Brachychampsa, as well as their close relatives the crocodiles and caimans.

Many of these ancient animals were survivors of the Cretaceous-Tertiary extinction, though no one knows why they lived when so many others perished.

Modern alligators are still closely related to their ancient ancestors and look much like their relatives did 80 million years ago.

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