Science
Notebook

Monday, April 23, 2007

Mystery Fossil Is Identified

What grew out of the ground like a 20-foot tree trunk, had no branches or leaves, and lived more than 100 million years before the dinosaurs?

For nearly a century and a half, scientists have been asking themselves and each other that question. The mystery revolves around the fossilized remains of an organism originally believed to have been an ancient evergreen and since hypothesized to have been an oversize alga, fungus or lichen.

Now a team of scientists has concluded that the bizarre life form, which no longer lives among us, was in fact a humongous fungus.

Prototaxites grew like a smooth-skinned, armless saguaro cactus 400 million years ago, a time when giant millipedes and other spineless creatures roamed among the first terrestrial plants. At the time, it was the largest land-based organism on Earth. But what was it?

After microscopic analysis of the organism's fossil fibers failed to settle the question, C. Kevin Boyce of the University of Chicago and Francis M. Hueber of the National Museum of Natural History in the District took a new tack. Working with colleagues from Harvard and the Carnegie Institution of Washington, they analyzed the fossil's carbon-atom variants, or isotopes.

Plants that use photosynthesis rely on atmospheric carbon dioxide as their source of carbon, so they tend to have a uniform ratio of carbon isotopes in their remains. But the team found that Prototaxites specimens varied considerably in their carbon composition. That suggests it was getting its carbon from varied sources in the ground -- strong evidence that the fossilized protuberance was the fruiting body of a giant fungus, they report in the May issue of the journal Geology, released today.

-- Rick Weiss

Fin Trade Imperils Basking Shark

Basking sharks continue to be hunted for their fins despite global protections for the world's second-largest fish, a new report indicates.

Using DNA analysis, researchers found fins from the sharks -- which have been declared endangered by the World Conservation Union and are under strict international trade regulations -- in both the Japanese and Hong Kong markets.

The findings, published in the online edition of the journal Animal Conservation, indicate that the trade in shark fins continues to pose a threat to the species. The sharks can grow as long as 40 feet and are considered vulnerable because they mature late and have few offspring.

"The demand for basking shark fins, which can fetch prices in excess of $50,000 for a single large fin, is continuing to drive the exploitation, surreptitious and otherwise, of this highly threatened species," said Mahmood Shivji, who led the research and directs the Guy Harvey Research Institute at Nova Southeastern University in Florida. "This finding, along with our recent research documenting extremely low genetic diversity in basking sharks worldwide, raises urgent concerns about the longer-term health of this species."

The scientists, who also came from the Pew Institute for Ocean Science, Imperial College London and Britain's Durham University, said they learned that when Chinese fin traders used the term "Nuo Wei Tian Jiu," they were often referring to basking sharks.

-- Juliet Eilperin

Bad Buzz on Mosquito Repellers

As mosquito season approaches, a new analysis has some bad news for people who use electronic high-frequency mosquito repellers to keep those annoying, sometimes disease-carrying insects at bay: They do not work.

High-frequency mosquito repellers are designed to drive away female mosquitoes by emitting high-pitched sounds that are almost inaudible to the human ear.

To evaluate the devices, the Cochrane Collaboration, which systematically evaluates a wide variety of scientific claims, reviewed the evidence for their effectiveness.

The researchers found 10 field trials that had been carried out in different parts of the world and that involved various species of mosquitoes. None showed any evidence that the devices work.

"All 10 studies found that there was no difference in the number of mosquitoes found on bare body parts of the human participants," said Ahmadali Enayati of the Mazandaran University of Medical Sciences in Iran, who led the work.

The review did not evaluate other devices to fend off mosquitoes.

-- Rob Stein