On an elusive search

SEARCH FOR A SPECIES

For 33 years, Peter A Rona has pursued an ancient, elusive animal, repeatedly plunging down more than two miles to the muddy seabed of the North Atlantic to search out, and if possible, pry loose his quarry. Like Ahab, he has failed time and again. Despite access to the world’s best equipment for deep exploration, he has always come back empty-handed, the creature eluding his grip. The animal is no white whale. And Rona is no unhinged Capt. Ahab, but rather a distinguished oceanographer at Rutgers University. He has succeeded in making an intellectual splash with a new research report, written with a team of a dozen colleagues.

One of the oldest living fossils

They have gathered evidence to prove that his scientific prey, an organism a bit larger than a poker chip, represents one of the world’s oldest living fossils, perhaps the oldest. The ancestors of the creature, Paleodictyon nodosum, go back to the dawn of complex life. And the creature was thought to have become extinct 50 mn years ago.

Rona said he looked forward to eventually capturing one of the creatures alive. It takes more than two hours to descend to the creature’s abode, which lies over two miles down. The environmental stability of that world, including its crushing pressures and icy darkness, means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

Rona has found that P. nodosum thrives in restricted areas of Atlantic seabed. Its only visible feature consists of tiny holes arranged in six-sided patterns that look like the hearts of Chinese checkers boards. He has photographed thousands of the hexagons and found that large ones have 200 or 300 holes. Rona’s inability to catch the creature itself means that even though scientists have given it the fossil’s name, they still debate what it is. The main question is whether the hexagonal patterns are burrows or body parts, vacant residences or animal remains.

“He’s got the drive of curiosity,” said Adolf Seilacher, a paleontologist at Yale and co-author of the new paper who first contacted Rona three decades ago to discuss the creature. Seilacher added that P. nodosum was an unusual animal, especially because the many holes at the surface of its abode link up below in a labyrinth of subsurface tunnels.

A complex way of life

“It’s not just any fossil but a demonstration of a very complex way of life,” he said in an interview. “It’s a building plan, a behaviour that makes this animal erect this gallery system. It’s a lifestyle that is very old.” By the early 1970s, armed with a doctorate in marine geology and geophysics from Yale, Rona was exploring the deep Atlantic for the National Oceanographic and Atmospheric Administration. He used dredges, cameras and echo sounders that mapped the seabed. In 1976, he stumbled on the living fossil.

Rona and his colleagues were towing a giant camera sled, its strobe lights firing every few seconds and recording the images on big reels of 35-mm film. Weeks later, Rona examined the freshly developed film. His head began to spin. What were all the holes? And what made the patterns?

He began interviewing the best marine biologists he could find, first in Florida, then in Washington at the Smithsonian Institution. No one had a clue. In 1978, Rona and a colleague, George F Merrill, published a paper that called the mystery animals “invertebrates of uncertain identity.” The breakthrough came soon thereafter. Seilacher, then at the Institute of Geology and Paleontology at the University of Tübingen, in Germany, wrote Rona to say the organism bore “perfect identity” with the fossil P. nodosum. He called the link “beyond any doubt.” In his letter, Seilacher suggested that the two scientists collaborate to study the creature.

The Atlantic site was too remote, too costly to scrutinise. In 1985, all that changed. Nearby, Rona and his colleagues discovered a riot of hot springs and bizarre life, including millions of shrimp. Suddenly, governments around the globe found the wherewithal to send oceanographers racing to the middle of the North Atlantic to explore the teeming springs.

Dives to hunt for living fossil

Rona’s creatures lay less than a mile way. He managed to visit the muddy site repeatedly, making dives in 1990, 1991, 1993, 2001 and 2003. On the latter dive, he and Seilacher went down together. Their collaboration made them improbable movie stars. In 2003, IMAX released ‘Volcanoes of the Deep Sea,’ featuring their hunt for the living fossil. Repeatedly, Rona tried to capture living specimens. He would have a hollow plastic tube lowered over a hexagonal spot and scoop up seabed mud. But detailed inspections never revealed anything of significance, no body parts, no biological fibers, no DNA.

The 2003 dive of Rona and Seilacher did, however, produce hard evidence that finally linked the animal to P. nodosum. The robot arm of the submersible Alvin directed a hose that squirted water at a hexagonal array of holes, slowly removing layers of mud. This revealed a hexagonal array of subsurface tunnels identical to those of the fossil. In May, the team’s new paper appeared in the online version of Deep-Sea Research, Part II, an oceanographic journal. It reviews the evidence of more than three decades and concludes that the hexagonal forms “are identical” with P. nodosum, backing the conclusion Seilacher reached long ago. The paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts.