It's been called the "terror of the Cambrian seas." More than half a billion years ago Anomalocaris swam the waters of the earth, searching for prey with its large, bugged-out eyes. Measuring more than two feet in length, it snagged its victims with long, shrimp-like claws, and pulled them toward a circular mouth that opened to reveal hundreds of sharp teeth. Nothing like it exists today.

A life-size model of Anomalocaris does exist, however, at the Peabody Museum. That is, at least, until an exhibit on fossils of the Burgess Shale closes on November 23. Burgess Shale: Evolution's Big Bang explores a period roughly 505 million years ago when a vast diversity of organisms exploded all at once onto the evolutionary scene. It was the first appearance on earth of most multicellular organisms-- some of which, like Anomalocaris, have no known descendants. The exhibition features fossils from the famed Burgess Shale site, along with some original fossils from the Peabody's collections and a reconstruction of life at Burgess Shale, as well as a couple of life-size models.

The Burgess Shale is located in eastern British Columbia, about 130 miles from Calgary, Alberta. Today, the area is rugged and mountainous, but when Anomalocaris existed, the site was on a muddy seabed near the edge of a towering reef. Mudslides buried the creatures, and layers of sediment preserved their bodies. But over time, as the earth experienced massive geologic changes, the fossils were brought to the surface, where they were discovered in 1909 by Charles Walcott of the Smithsonian Institution. He collected more than 65,000 specimens at the site.

In the 1970s, Dr. Harry Whittington of Cambridge University engaged in a restudy of Walcott's fossils, assisted by two graduate students. One of the students, Derek Briggs, recently became curator of invertebrate paleontology at the Peabody. Briggs calls it a "happy coincidence" that the Smithsonian's exhibition is making a stop in New Haven so soon after he arrived at the museum.

But Briggs's association with the Burgess Shale is more than peripheral. It was Briggs, in fact, who helped piece together what Anomalocaris actually looked like, after nearly a century of misinterpretation. In the 1880s a researcher had found just the shrimp-like claws of the creature and named it Anomalocaris (meaning "odd shrimp"). Some 40 years later another scientist found only its round mouth and thought it was a kind of jellyfish. But with much study of Walcott's and other specimens, Briggs was able to determine that these were actually parts of the same animal.

The self-effacing paleontologist is quick to point out the greater significance of the Burgess Shale find as a whole. "Until recently, Burgess Shale was the only locality in which one found early multicellular organisms so well preserved," says Briggs. Now there are sites around the world. But of the 120 different types of animals found at Burgess Shale, Briggs adds, "only 16 percent had hard shells; the rest were completely soft-bodied and not normally fossilized. Burgess Shale provided a lot of information on what these creatures really looked like, and helped form the first complete picture of the early evolution of multicellular organisms."