• David is a Deputy News Editor specializing in coverage of science policy, energy and the environment.

Fan of Decomposition? Have We Got Something for You

24 May 2013 5:30 pm

Courtesy of Mark Purnell

Top: Going, going, gone. A lamprey snout (far left) is reduced to just a few bones after 296 days of decay (far right).

Bottom: Don't lose your head. After 48 days, a hagfish skull (far left) nearly disappears (far right).

Portraits of putrefying fish might not spark bidding wars at Sotheby's, but they're making a hit with fossil researchers. A new Atlas of Vertebrate Decay, filled with photos of rotting hagfish, sharks, and lampreys, promises to help paleontologists identify ancient creatures that got squashed and scrambled during the process of fossilization.

Fossils have long provided researchers with critical evidence of how life evolved, revealing how structures such as fins, feathers, jaws, and backbones developed over time. But often the remains can be hard to interpret. Scavengers can jumble and break bones and shells, rot dissolves signature soft tissues, and geologic forces flatten 3D carcasses into papery imprints. To make sense of such puzzles, paleontologists often try to match fossils to modern, living organisms, looking for similar features.

The problem, says paleobiologist Mark Purnell of the University of Leicester in the United Kingdom, "is that most fossils preserve decomposed remains, so we should be comparing the fossil to rotting things, not living animals. But there's often no database of what rotting things look like." One result: Researchers studying the evolution of early vertebrates have sometimes spent decades fiercely debating whether a particular fossil represents a big news missing link, or just another mangled carcass.

To make comparisons easier, Purnell and two colleagues, Leicester's Sarah Gabbott and Robert Sansom, now at the University of Manchester, decided to take on some "smelly and unpleasant but useful research." First, they collected living specimens of six species that researchers believe are similar to early vertebrates, including the Atlantic hagfish (Myxine glutinosa), jawless lampreys, a couple of sharks, and the fishlike chordate known as Amphioxus. It wasn't easy: Hagfish, for instance, produce copious amounts of slime, and Sansom had to empty a suitcase full of goop while returning by train from a collecting trip to Sweden. "The slime was leaking out the zipper, and some of the other passengers complained," Gabbott says. Once back at the lab, the team let specimens rot in water for as long as 300 days, periodically photographing the disintegration.

The images are the heart of the atlas, published in this month's issue of Palaeontology. Sometimes, they show that "what may be the most useful [body] parts for identifying a fossil rot away first," Gabbott says. Soft cartilage and distinctive muscle tissues, for instance, can melt away within weeks. But the atlas also highlights hardier structures that could help scientists separate special fossils from the ordinary. A decayed shark, for instance, looks suspiciously like an "enigmatic," 400-million-year-old fish fossil found in Scotland that some researchers believe could be an early vertebrate ancestor, Purnell says.

The authors of the atlas "have done fantastic, important work by making stuff rot," says paleontologist Jason Head of the University of Nebraska, Lincoln. Researchers trying to piece together evolutionary trees "can be misled by fossils," he says, "because we only see what is preserved, not decayed away. But understanding what was there and isn't now can be really important to getting it right."

For his part, Purnell concedes that that the atlas isn't for the squeamish. Still, he says, "every coffee table should have one."