Fossils from Greenland have revealed that mysterious squid-like animals called nectocaridids are not early cephalopods as was previously thought, but ancient – and fearsome – relatives of arrow worms, predatory marine invertebrates that live in our oceans today.
The 500-million-year-old fossils, some of which contain the animals' digestive systems (with prey still inside), muscles and even their nervous systems, were collected over nine years of expeditions to Sirius Passet in North Greenland, a site famous for its exceptionally well-preserved marine organisms from the Early Cambrian period around 518 million years ago.
Researchers say the study, published in the journal Science Advances, provides evidence that today's relatively simple arrow worms had complex ancestors that sat high in the ocean food chain.
- Giant pre-historic worms discovered in Greenland
- Muscles and guts of prehistoric animal found “preserved in unimaginable detail” in South African mountains
Delicate fossils help solve 500-million-year-old puzzle
“Around 15 years ago a research paper, based on fossils from the famous Burgess Shale, claimed nectocaridids were cephalopods,” explains Dr Jakob Vinther, associate professor of macroevolution at the University of Bristol (who co-led the study with the Korean Polar Research Institute and University of Copenhagen).
“It never really made sense to me, as the hypothesis would upend everything we otherwise know about cephalopods and their anatomy didn’t closely match cephalopods when you looked carefully,” says Vinther, who made it his mission to solve the puzzle.
The breakthrough came when researchers analysed 25 specimens of nectocaridids from Greenland and discovered “preserved parts of their nervous system as paired mineralised structures”. Vinther says the finding was a giveaway as to where these animals sit in the tree of life.
- Drone captures Greenland ice tearing open to reveal humungous animal beneath
- Colossal flood explodes through Greenland Ice Sheet. What scientists find in aftermath astounds them
Further finds in Sirius Passet revealed arrow worm fossils with a distinctive ventral ganglion, a cluster of nerves unique to this group. “We now had a smoking gun to resolve the nectocaridid controversy,” says Dr Tae-Yoon Park of the Korean Polar Institute.
“Nectocaridids share a number of features with some of the other fossils that also belong to the arrow worm stem lineage. Many of these features are superficially squid-like and reflect simple adaptations to an active swimming mode of life in invertebrates, just like whales and ancient marine reptiles end up looking like fish when they evolve such a mode of life,” Park explains.
The fossils suggest nectocaridids were advanced predators with complex eyes similar to ours, swimming appendages and long antennae.
“Our fossils can be much bigger than a typical living arrow worm and combined with their swimming apparatus, eyes and long antennae, they must have been formidable and stealthy predators,” says Vinther.
Find out more about the study: A fossilized ventral ganglion reveals a chaetognath affinity for Cambrian nectocaridids
Top image: Greenland (not exact location of fossil discoveries). Credit: Getty
More amazing wildlife stories from around the world
- "The most transcendent wildlife experience”: ocean safari stumbles upon thousands of diamond-shaped rays
- Remember Cecil, shot 10 years ago by a trophy hunter? This is what happened next – and it’s good news
- Drone spots more than 1,000 "ghost-like" animals off Mexican coast
- More than 1,000 rattlesnakes caught in Michigan wetlands. What scientists find in their DNA is concerning
