Fossil feast for 'zombie worms'

Osedax worms living on a whale bone (c) N Higgs Scientists are just beginning to understand bone-eating "zombie worms"

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Traces of bone-eating "zombie worms" have been found in a three-million-year-old fossil from Italy, say researchers.

Osedax worms feed on whale skeletons on the seabed using root-like tissues to bore into and dissolve the bones.

Scientists from the Natural History Museum in London identified telltale borings in the fossil using a scanner.

The discovery suggests the worms were much more widespread throughout prehistoric oceans than thought.

The findings of lead scientist Nicholas Higgs and colleagues are published in the journal Historical Biology.

The only other evidence of Osedax worms in the fossil record was found off the coast of Washington state, US, last year.

WHAT IS A WHALE FALL?

Whalefall by Craig Smith NOAA (oceanexplorer.noaa.gov) [Public domain], via Wikimedia Commons
  • When whales die they sometimes wash up on shore but the majority fall to the seabed in the deep ocean
  • For organisms living at these depths a 'whale fall' is a banquet, attracting the attention of sharks and worms alike
  • The carcasses can support diverse communities for decades

Mr Higgs, a PhD student at the University of Leeds, was investigating Osedax worms for his studies with scientists at the Natural History Museum, London and made contact with staff at the University of Florence's Museum of Natural History in Italy.

Staff had previously discovered a whale fossil surrounded by other fossilised organisms that suggested an ecosystem had developed around the carcass.

These 'whale falls' provide ideal conditions for bone-eating worms so Mr Higgs travelled to Italy to investigate the fossils.

"We didn't find any [traces] on that whale skeleton in particular... but I spent a week there searching through all their collections and I eventually found this bone in a dusty box," Mr Higgs told BBC Nature.

"This bone had been collected in 1875 so it had been in the collection for ages just gathering dust. It wasn't a very good whale specimen so it never really got put out on display," he said, explaining that pristine examples are more often sought for identification.

But the damage to the bone was familiar to Mr Higgs and back in London his suspicions were confirmed using the Natural History Museum's micro-CT scanner to investigate the fossil in detail.

"Fossils of worms are really rare. We don't know a lot about their fossil record because they're soft animals," he said.

"But, because these particular worms leave characteristic borings, we can trace them."

Zombie nickname

Osedax worms do not have a mouth or gut but invade bones with fleshy root tissues to extract nutrients, earning them the "zombie" nickname.

Whale bone fossil (c) Natural History Museum The riddled fossil gives clues to the worms' mysterious history

They bore into bones leaving distinctive bulb-shaped cavities that are not made by any other species.

This group of worms were first discovered in 2002 and have been recorded in the Pacific and Atlantic oceans but not the Mediterranean Sea.

The descriptively named bone-eating snot-flower worm (Osedax mucofloris) was discovered off the coast of Sweden, also by scientists from the Natural History Museum, London.

However, the boreholes made by this species differ in shape from those found in the fossil.

Rather than simply the same species in a different location, Mr Higgs suggests there could be an as-yet unidentified species of Osedax living in the Mediterranean Sea that evolved from the animals that left the fossilised traces.

"It's just a matter of looking... but it's not very often you come across a dead whale at the bottom of the sea floor," he added.

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