Tracing bone-eating deep sea worms back through time - November 11, 2009
The fossils of whales and plesiosaurs may contain evidence allowing modern scientists to understand the evolution of one of the strangest creatures in the sea.
Osedax worms live by burrowing into the bones of mammals that sink down to the bottom of the sea. Once ensconced on a nice decomposing whale or seal the worms mature into sexual females and acquire a harem of microscope males that live in the gelatinous tubes that surround them.
In a new paper in BMC Biology Robert Vrijenhoek, of the Monterey Bay Aquarium Research Institute in the United States, and his colleagues say there are at least 17 different species of Osedax, not just the five previously described.
While the team's genetic and morphological analysis has teased out more about the evolutionary relationships between these worms, a big question remains: when did Osedax appear on the global bone-devouring scene?
One possibility is that they split from their worm ancestors about 45 million years ago when ancient whales appeared. Another theory posits they appeared at least 20 million years before the appearance of large marine mammals.
Osedax are soft bodied, so they do not generally leave decent fossils. However if they were around back in the day they may well have bored distinctive holes into the bones of ancient creatures in much the same way as modern Osedax put holes in modern carcasses.
“Consequently, we have distributed whalebones containing Osedax to several paleontologists who are also examining the taphonomy of fossilized bones from plesiosaurs and cetaceans,” write Vrijenhoek and co. “It is to be hoped that these efforts will help us to narrow the age of this remarkable genus of bone-eating worms.”
Vrijenhoek tells Nature that one palaeontologist is already CT scanning some cow bones with Osedax holes in the hope of developing tools to detect traces in fossil whalebones. Other researchers – including those working on Cretaceous plesiosaurs – are also being enlisted in the great historical worm hunt.
Image: Greg Rouse
