zombie worms
Bone-eating zombie worms ate pleasiosaurs 100 million years ago.Nick Higgs

"Zombie worms" feasted on the bones of giant marine reptiles, including pleasiosaurs and sea-turtles, 100 million years ago, scientists have discovered.

Osedax – the bone-eating worm – has been dated back to prehistoric times, originating at least 100 million years ago.

Publishing their findings in the Royal Society journal Biology Letters, researchers at the University of Plymouth found traces of Osedax on plesiosaur fossils held at the University of Cambridge Museum.

They said it is the first fossil evidence that the bone-eating worm species originated and thrived in the Mesozoic period – and that these important evolutionary creatures appeared before whales in the Cenozoic and survived beyond the End Cretaceous Mass Extinction.

"Although plesiosaurs went extinct at the end-Cretaceous mass extinction (66 million years ago), chelonioids survived the event and diversified, and thus provided sustenance for Osedax in the 20 million year gap preceding the radiation of cetaceans, their main modern food source," they wrote.

"This finding shows that marine reptile carcases, before whales, played a key role in the evolution and dispersal of Osedax and confirms that its generalist ability of colonising different vertebrate substrates, like fishes and marine birds, besides whale bones, is an ancestral trait."

Osedax worms are about finger length and are found in oceans across the world at depths of up to four kilometres. They lack a mouth or digestivge system, but instead penetrate bone by using root-like tendrils, through which they can absorb bone collagen that is then converted into energy.

Normally, they eat whale bones, which had led some scientists to speculate they evolved with whales 45 million years ago. However, the scientists used a computed tomography scanner to discover bore holes from these creatures in the pleasiosaurs.

Nicholas Higgs, from the university's Marine Institute, said their findings have implications for the fossil record: "The exploration of the deep sea in the past decades has led to the discovery of hundreds of new species with unique adaptations to survive in extreme environments, giving rise to important questions on their origin and evolution through geological time.

"The unusual adaptations and striking beauty of Osedax worms encapsulate the alien nature of deep-sea life in public imagination. And our discovery shows that these bone-eating worms did not co-evolve with whales, but that they also devoured the skeletons of large marine reptiles that dominated oceans in the age of the dinosaurs. Osedax, therefore, prevented many skeletons from becoming fossilised, which might hamper our knowledge of these extinct leviathans.

"The increasing evidence for Osedax throughout the oceans past and present, combined with their propensity to rapidly consume a wide range of vertebrate skeletons, suggests that Osedax may have had a significant negative effect on the preservation of marine vertebrate skeletons in the fossil record. By destroying vertebrate skeletons before they could be buried, Osedax may be responsible for the loss of data on marine vertebrate anatomy and carcass-fall communities on a global scale."