Ichthyosaurs and plesiosaurs were a major part of life in the oceans between the Triassic and Cretaceous Periods. © The Trustees of the Natural History Museum, London
By James Ashworth
After large animals die in the deep sea, a community of creatures move in to feast on their remains.
New research shows that key members of these communities, the bone-eating worms, have been cleaning up the ocean floor for over 100 million years.
The bones of ancient marine reptiles supported a thriving ecosystem after their death.
When large marine animals like whales die, they sink down to the seabed. Once their flesh has been stripped away by scavengers and microbes, their corpses are colonised by a variety of specialised invertebrates that feast on the fats and proteins locked inside their skeletons.
These bone-eating communities are ancient, and have been on Earth for at least 100 million years. Before whales existed, bone-eating worms were eating into the skeletons of mosasaurs, ichthyosaurs and plesiosaurs – leaving their distinct burrows behind in the process.
New research, published in the journal PLOS One, has named seven of these burrow types. Sarah Jamison-Todd, a PhD student who led the research, says that although the researchers can’t be precisely sure which species made the holes preserved in fossil bones, some are very similar to the burrows of living bone-eating Osedax worms.
“We haven’t found anything else that makes a similar burrow to these animals,” Sarah explains. “As the ancient bores are so similar to modern Osedax species, and we don’t have body fossils to contradict us, we assume that they were made by the same or a similar organism.”
“It shows that the bone-eating worms are part of a lineage that stretches back at least to the Cretaceous, and perhaps further. We can see how the diversity of bone-eating worms changes across millions of years.”
Bone worms (the red animals in this picture) were first discovered in the early 2000s, but these animals are believed to have evolved over 100 million years ago. Adapted from © Fujiwara et al. via Zookeys, licensed under CC BY 4.0.
Bone-eating worms play an important role in recycling the ocean’s nutrients. But despite this vital function the first Osedax species were only discovered in 2002, with dozens more species described since.
The worms can be found in oceans from the Arctic all the way down to the Antarctic. They live at a range of depths, from just 20 metres beneath the surface to more than four kilometres deep.
What makes their lives even more extraordinary is that they don’t even have a mouth or anus. Instead, Osedax worms rely on bacteria to break down the skeletons for them before absorbing the released nutrients through a root-like system.
It appears that this symbiotic relationship between the worms and bacteria is truly ancient. Fossilised bones and teeth from plesiosaurs, ancient whales and turtles from the last 100 million years preserve the boreholes of these worms.
Fossilised traces of animal activity like the bone burrows can’t be named as full species but can be described as an ‘ichnospecies’.
Different species of modern bone-worm create different shaped burrows which can then be used to identify the worms down to species levels. The researchers looking at these fossil traces suspected that the same thing could be done with the ancient burrows.
The team searched for external evidence of Osspecus burrows before scanning suitable fossils. © Jamison-Todd et al.
To start their search, the team turned to the vast array of marine reptile fossils looked after by the Natural History Museum. Dr Marc Jones, who curates this collection, says that the team needed to start by getting an accurate date for the bones.
“Some of these specimens were collected in the 1800s, and the information on them can be very brief so it’s difficult to know exactly where they’re from,” Marc explains. “We focused on specimens from the Chalk of the UK, as our colleagues have been working on better understanding these Cretaceous ecosystems using museum collections.”
“They’re also working to date fossils of an unknown age. By using the remains of small organisms that make up the Chalk itself, we were able to date the fossils to more precise time slices of the Cretaceous Period.”
The team then searched for signs that the fossils had been bored into. In addition to the more obvious collapsed burrows, the team closely examined the bones and teeth for borehole entrances the size of pinholes.
“We examined over 130 different fossils for signs of bone-eating worm burrows,” Sarah says. “However, not all fossils which look like they’ve been bored into by these worms have been – it could have been caused by different animals or environmental weathering.”
“The only way to really confirm this is to put the fossils under a CT scanner. This allows us to create 3D reconstructions of the inside of the bone and see the different patterns that have been left behind.”
CT scans (inset) have been used to digitally reconstruct the unique burrow shapes left behind by different bone-eating worms in the Cretaceous. © Jamison-Todd et al.
In total, the researchers identified a set of six burrows in bones and teeth that represent new bone-worm ichnospecies. They also included a previously studied fossil from the Royal Belgian Institute of Natural Sciences, bringing the total number of new ichnospecies to seven.
The team drew on a variety of different sources to inspire their new names. Some refer to the shape that the worms leave behind in the bone, with Osspecus arboreum’s looking like a tree. Osspecus morsus, meanwhile, was named after the Latin word for ‘bite’ because it’s mostly found in fossil teeth.
Another species, Osspecus eunicefooteae, was named in honour of Eunice Newton Foote, a scientist whose pioneering research into the greenhouse effect was overlooked for more than a century. She was the first person on experimental grounds to suggest that greater amounts of carbon dioxide in the atmosphere would increase Earth's temperature.
The team hope that naming the different types of burrows will make it easier for other scientists to find these traces in other fossils and document their true diversity.
“There are many more examples of boring that haven’t yet been named from both ancient and modern bone-eating worms,” Sarah adds. “In fact, some bores from the Cretaceous appear to be similar to ones that are still made today.”
“Finding out whether these burrows are made by the same species, or are an example of convergent evolution, will give us a much better idea of how these animals have evolved, and how they have shaped marine ecosystems over millions of years.”
Find out more about why we need to protect the oceans, find themed events, and read about the pioneering work of the Museum's marine scientists.
Don't miss a thing
Receive email updates about our news, science, exhibitions, events, products, services and fundraising activities. We may occasionally include third-party content from our corporate partners and other museums. We will not share your personal details with these third parties. You must be over the age of 13. Privacy notice.
Follow us on social media