Discover, January 31, 1995
“We take crayfish for granted,” says Steven Hasiotis, a paleontologist at the University of Colorado. “People have grown up with them, chased them around, put them in their aquariums, gotten yelled at by their moms for keeping them. I knew two or three people who had to flush theirs down the toilet.” But at a Geological Society of America meeting last May, Hasiotis reported a new reason to respect these commonplace crustaceans. Crayfish were once thought to have originated 140 million years ago, but Hasiotis has discovered 220-million-year-old specimens that are almost identical to modern ones. He thinks crayfish may be as much as 300 million years old. That would put them in a class with roaches and sharks as some of the most enduring animals in history.
Crayfish look much like their close relative the lobster, but they’re freshwater animals. They live in burrows in lakes, rivers, and streams; some species can even thrive miles away from a body of water by digging down to the water table. It was burrows that first put Hasiotis on the trail of his ancient crayfish. In the late 1980s he was studying some puzzling tubular holes in 220-million-year-old rocks from southeastern Utah–holes that previous researchers had suggested were lungfish burrows. (Some lungfish tunnel into the mud when their pond dries up.) But Hasiotis couldn’t find a single fossilized fish scale or tooth in the rocks. He also noticed that the Utah holes didn’t look like the simple, 3-foot-deep shafts that lungfish dig: some were 12 feet deep, others were shallow, interconnected chambers, and still others were U-shaped tunnels. Hasiotis started thinking about crayfish.
At the time, the idea was heretical: the earliest known crayfish had lived in salty coastal areas 130 million years ago. Most researchers assumed that crayfish had descended from lobsters around that time and gradually made their way inland. “My adviser said, ‘You’ve got a lot of guts saying that. You think you can tell this from the burrows? It’s not going to hold water until you find some fossils,'” recalls Hasiotis. For a couple of field seasons, he had no luck. “I remember saying, ‘Dear God, help me out here, because I really need a fossil.'” In 1989, Hasiotis’s prayers were answered–he found a fossil crayfish in one of the burrows. Since then he has found hundreds more.
Just as important, he has found that crayfish 220 million years ago were as varied in body and burrow as they are today. The shape of a crayfish burrow and of the animal itself depend on how close it lives to water. A crayfish a few miles from water uses shovel-like claws to dig a deep shaft to the water table; there it excavates a complex of several chambers in which it spends almost all its time. A crayfish in a pond, however, digs a shallow, simple burrow. Its claws make less impressive shovels, but it has spines to protect itself from fish and amphibian predators, as well as a large, powerful tail for quick escapes. Hasiotis found all these special adaptations and more in his fossils. “If it weren’t for being squashed flat and preserved in rocks, they’d look nearly identical to modern crayfish,” he says.
Such specialization doesn’t happen overnight. Hasiotis believes crayfish must have evolved as early as 300 million years ago–and not from lobsters, which didn’t exist back then. In fact, he turns conventional wisdom on its head: he says lobsters may be descended from a crayfish that, for whatever reason, returned to the sea.
Copyright 1995 Discover Magazine. Reprinted with permission.