Osedax worms—also called “zombie” worms—live off the bones of dead creatures. Several species of Osedax surfaced in Monterey Bay, California, in 2002, and evidence of them has now been found in the Mediterranean in a fossilized whale bone. These bone-destroying worms have evidently existed across the globe as long as animals have, which raises a question: If the fossilization of bones requires vast timespans, why didn’t Osedax consume them before they could be mineralized?

An Osedax has no mouth. It instead absorbs its nutrients through branched appendages that grow down into the bone, while a tube-shaped stalk suspends fan-like gills into the surrounding seawater.1 The worm provides the perfect home for a species of symbiotic bacteria that erode the bone.2

After Monterey’s deep-water Osedax discovery, researchers found more when they submerged and monitored a whale carcass in the Atlantic Ocean.3 Now, the characteristic cave-shape holes made by the worms have been recognized in the whale bone fossil from Tuscany in Italy.4 Has any ocean never had them?

Osedax holes have appeared in some of the lowermost whale bone fossils in the rock record, so the worms have been around at least as long as whales. But that also means that the whale bones could only have hardened into stone rapidly, before the worms could eat them.

Nature author Matt Kaplan wrote that since Osedax boreholes are found in bird fossils located in older dinosaur rocks, Osedax “could have evolved alongside whales roughly 30 million to 40 million years ago during the Paleogene period, or they could have evolved 70 million to 80 million years ago during the Cretaceous.”4

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