Discovery of a giant parasitic worm with jaws, dated 165 million years ago

Researchers have recently described a new species of parasitic worm, showcasing rather unexpected characteristics that thrived during the Jurassic period.

Juracanthocephalus daohugouensis

Reaching several meters in length, spiny-headed worms are known to parasitize various vertebrates. While previous fossils of acanthocephalans were found in the digestive systems of long-extinct creatures, the new species, named Juracanthocephalus daohugouensis, was unearthed from the bed of an ancient volcanic lake.

This species is by far the oldest acanthocephalan ever discovered, dating back 165 million years, and the analysis of this remarkably well-preserved male specimen revealed some quite unexpected features.

J. daohugouensis possessed jaws, a trait distinguishing it from its modern relatives and also suggesting the presence of a functional intestine. Since acanthocephalans are known for their significant sexual dimorphism, the authors of the new study, published in the journal Nature, estimate that females would have been considerably larger.

165-Million-Year-Old Fossil Is New Species Of Ancient Parasite. Did It Come From A Dinosaur’s Butt?https://t.co/ChjgLfFhXl

— IFLScience (@IFLScience) May 10, 2025

The team suggests that the spiny-headed worms’ current parasitism of birds and crocodiles, which are related to dinosaurs, indicates that they were also wreaking havoc among these giant reptiles.

Prehistoric Tapeworms

Last year, researchers described the very first fossil of a tapeworm, or solitary worm, dating back to the Cretaceous. This specimen was discovered in an unexpected setting: a fragment of amber from Burma that is 100 million years old.

This amber likely formed on a prehistoric coastline, suggesting that the parasite was lurking inside the remains of a cartilaginous fish washed ashore. The carcass of the fish would have been consumed by either a predator or a land scavenger, and the detached tentacle became trapped in the resin of a nearby plant.