A pinworm that lived 240 million years ago and infected the ancestors of mammals has been identified by scientists from an egg found in a tiny piece of fossilised dung.
The discovery confirms that herbivorous cynodonts - the ancestors of mammals - were infected with the parasitic pinworm.
Believed to be the most ancient pinworm to be found in the fossil record, the pinworm egg, representing an undescribed or new species, was named Paleoxyuris cockburni, in honour of Aidan Cockburn, founder of the Paleopathology Association.
"This discovery opens the door to finding additional parasites in other species of fossil organisms," said Scott Gardner from the University of Nebraska in the US.
It also makes it even more likely that herbivorous dinosaurs carried pinworms, the researchers noted.
The team found the pinworm egg in coprolite - fossilised faeces - collected in 2007 at an excavation site in Brazil.
The study appeared in the journal Parasites & Vectors.