Science

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.