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Part of the Dinosaurs: Ancient Fossils, New Discoveries exhibition.

Global forest fires. Acid rain. Tsunamis. Skies dark for months or years with volcanic ash. How could anything have survived? Roughly half of all species on Earth died out 65 million years ago. What about the other half? How did they make it?

Scientists aren't sure. Some have suggested that animals that lived in burrows survived. Others argue that plants and animals with a higher tolerance of acid rain would have had a survival advantage. Still others reason that an animal's diet might have been a crucial factor: Animals that did not depend on one food source but ate a varied diet--roots, seeds, insects, decaying plants or other animals--might have been able to make better use of available resources. Although we don't understand exactly why, a range of species--from birds to frogs to mammals--lived and flourished. All species alive today are descendants of species that survived the mass extinction 65 million years ago.

Family Resemblance

CROCODILES AND ALLIGATORS belong to a large family called the crocodilians. These animals all look remarkably similar: the general body form has changed little in the past 80 million years. Somehow crocodilians emerged essentially unchanged from the dramatic events of 65 million years ago that wiped out many of their relatives. The crocodile Borealosuchus lived alongside dinosaurs like T. rex. Relatives of this species can be found in the more recent fossil record as well as in the wild today.

Crocs and Dinos

When fully grown, a 70-million-year-old crocodile could reach 4.5 meters (15 feet) in length. Other crocodiles of this era may have been more than twice as long. Crocodilians lived alongside dinosaurs for millions of years.

Ancient Alligator

The second-oldest alligator species known lived just over 16 million years ago in the middle of the North American continent. This species was smaller than living alligators, reaching only around two meters (6.5 feet) in length.

Familiar Face

Once an endangered species, the American alligator now lives in rivers and swamps across much of the southeastern United States, from North Carolina to Texas. Its skull looks remarkably similar to that of its ancient relatives.

We Will Survive

All crocodiles and alligators alive today can trace their roots back to creatures that survived the mass extinction that wiped out all nonavian dinosaurs.