Diving deep for a living fossil

Oceanographer Peter A. Rona has been on the trail of an ancient animalonce thought to have become extinct 50 million years agofor over three decades....

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. Despite access to the worlds best equipment for deep exploration,he has always come back empty-handed,the creature eluding his grip.

The distinguished oceanographer at Rutgers University has now succeeded in making an intellectual splash with a new research report,written with a team of a dozen colleagues. They have gathered enough evidence to prove that his scientific preyan organism a bit larger than a poker chiprepresents one of the worlds oldest living fossils,perhaps the oldest. The ancestors of the creature,Paleodictyon nodosum,go back to the dawn of complex life. The creature,known from fossils,was thought to have become extinct 50 million years ago.

Rona said he looked forward to eventually capturing one of the creatures alive. I think its likely, he said,if we can do the dives. Rona,an authority on the deep sea,likes nothing better than to cram himself into a tiny submersible and fall into the abyss. It takes more than two hours to descend to the creatures abode,which lies more than two miles down. The environmental stability of that worldincluding its crushing pressures and icy darknessmeans that some of its most famous inhabitants have survived for eons as evolutionary throwbacks,their bodies undergoing little change.

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

Hes 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 said P. nodosum was a most unusual animal,especially because the many holes at the surface of its abode link up below in a labyrinth of subsurface tunnels. He added that the earliest forms of Paleodictyon dated to the explosion of complex life in the Cambrian period some 500 million years ago. The animals began existence in shallow waters,he said,and gradually expanded into the dark habitats of the deep sea.

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. 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,lighting up the seabed and recording the images on big reels of 35-mm film. Weeks later,back in his Florida office,Rona examined the freshly developed film. What were all the holes? In 1978,Rona and a colleague,George F. Merrill,published a paper that ruled out many possibilities and 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 to Rona to say the organism bore perfect identity with the fossil P. nodosum.

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Piggybacking on high-priority missions,Rona managed to visit the muddy site in the Atlantic repeatedly,making submersible dives in 1990,1991,1993,2001 and 2003. On the latter dive,he and Seilacher went down together. 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 a thick core of seabed mud. But detailed inspections of the muck never revealed anything of significanceno body parts,no biological fibres,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. The operation revealed a hexagonal array of subsurface tunnels identical to those of the fossil.

The paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts. Seilacher,who backs the burrow idea,sees the tunnels as a kind of farm where an unknown type of worm or other organism raises micro-organisms to eat. Rona sees the holes as body parts,perhaps from a type of compressed sponge. The lack of biological clues,he said,may arise because microbial predators eat the remains after the creatures die.