Posted by: The ocean update | October 31, 2011

Bone-Eating Zombie Worms Found in Whale Fossil

3D CT scan of a bone-eating "zombie" worm from the genus Osedax, showing the canals it makes into the bone. (Natural History Museum)

Oct 31, 2011. Canals made by worms from the genus Osedax have been found in a 3-million-year old whale bone from the Mediterranean Sea off Italy.

Osedax worms have no mouth or gut, but use root-like tissues to extract nutrients from vertebrate skeletons on the sea bottom, hence their zombie nickname. There is the potential that they have destroyed much of the marine fossil record

These worms were only discovered in 2004, and occur throughout the Pacific and Atlantic Oceans. A previously found fossil has shown traces of Osedax worms from the Pacific 30 million years ago.

This new paleogeographic evidence of Osedax shows that these zombie worms also inhabit the Mediterranean, and suggests that they were widespread even back then.

Osedax worms form part of specialized communities called “whale falls” that live in carcasses on the ocean floor. Different species appear to prefer different bone parts with some inhabiting the surface and others burrowing deep inside.

By looking at the canals in a fossilized whale bone from the Pliocene period, a team of researchers identified borings specific to Osedax species.

Using microcomputer tomography, the team studied the borings in detail without damaging the fossil. They compared it with canals from living zombie worms, and with different bone-eating creatures such as other marine worms and bivalves.

“At first I was skeptical, but the more I investigated the borings, the more confident I became that these borings were caused by Osedax, so it was a slow build up of excitement,” said lead researcher Nicolas Higgs from the UK’s Natural History Museum and University of Leeds in a press release.

“Identifying Osedax traces was one of the main aims of my research project, but finding these small borings is like finding a needle in a haystack so I felt pretty lucky too.”

The canals are referred to as trace fossils because they provide evidence of the activity in the absence of the animal itself. Worm fossils are rare because they have no skeleton. The ancient worms have been given the species name Osspecus tuscia, meaning “bone cavern of Tuscany.”

The Mediterranean Sea dried up around 6 million years ago, becoming isolated and very salty with most of its inhabitants extinguished until it refilled around 5.3 million years ago, when the Atlantic Ocean rejoined it.

Osedax was found after the refilling of the Mediterranean occurred so was probably living in the Atlantic since this is where Osedax would have entered from,” Higgs said.

“Our results tell us that Osedax worms were very widespread throughout the world’s oceans in the past and so may have had a significant negative effect on the global fossil record of whales, since they were destroying the bones.”

Some whale bones were probably totally degraded before they could be fossilized, meaning experts now need to re-examine the whale fossil record to account for any eaten bones.

The findings were published online in the journal Historical Biology on Oct. 24.




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