Bone-eating Worms 30 Million Years Old
|This 30-million-year-old rib fragment of a whale shows circular boreholes made by Osedax. Courtesy of University of Kiel|
Six years ago, Osedax, a worm that consumes whale bones on the deep-sea floor, was first described based on specimens living on a whale carcass in 2891-meter depth off California. Since then, paleontologists have been searching for fossil evidence to pin down its geologic age. Now, researchers have found 30-million-year-old whale bones with boreholes and excavations matching those of living Osedax in size and shape, leading them to conclude that the “boneworms” are at least 30 million years old.
The fossil bones belong to ancestors of our modern baleen whales, and their age was determined using so-called co-occurring index fossils. To produce accurate images of the boreholes, the fossil bones were CT-scanned by scientists at the Institute of Geosciences at the Christian-Albrechts-University at Kiel, Germany.
“The age of our fossils coincides with the time when whales began to inhabit the open ocean,” explains paleontologist Steffen Kiel, who has been working on the evolution and fossil history of deep-sea ecosystems for many years. Only from the open ocean could dead whales sink to the deep-sea floor where they served as food for the boneworms.
“Food is extremely rare on the vast deep-sea floor, and the concurrent appearance of these whales and Osedax shows that even hard whale bones were quickly utilized as food source,” Kiel explains.
The ancient bones were found by the American fossil collector Jim Goedert, who has been collecting fossils along the American Pacific coast for more than 30 years and is well-known in the scientific community. Kiel has done several field trips with Goedert to the U.S. Pacific coast, a geologically active area where fossil-rich sediments are continuously uplifted by plate tectonic processes.
Vertebrate paleontologists are probably less happy about the old age of Osedax: because it has been feeding on bones for most of the evolutionary history of whales, it is likely to have destroyed many potential whale fossils.
This result was published in the Proceedings of the National Academy of Sciences on April 19, 2010.