Giant millipedes as long as a car and weighing 50kg once hunted across northern England, experts have said, following the discovery of a 326 million-year-old fossil.
The fossil was found by "fluke" when a section of a cliff fell at Howick Beach in Northumberland and was discovered by a former PhD student.
Experts said in order to get so big, the creature, known as Arthropleura, must have found a nutrient-rich plant diet and may even have been predators, feasting on other invertebrates or small amphibians.
Only a section of the fossil has been found, according to experts.
They believe the specimen is a section of the creature's exoskeleton that it shed near a river bed, which was then preserved by the sand.
"It was a complete fluke of a discovery," said Dr Neil Davies, from Cambridge University's Department of Earth Sciences and lead author of a paper on the fossil.
"The way the boulder had fallen, it had cracked open and perfectly exposed the fossil, which one of our former PhD students happened to spot when walking by."
The segment that was found measures to around 75cm long, but scientists believe its entire body could have measured around 2.7m long and weighed 50kg.
The fossil was taken to Cambridge for analysis after receiving permission from Natural England and the landowners, the Howick Estate.
It was so big it required four people to carry it.
The fossil is made up of multiple articulated exoskeleton segments and is broadly similar to the modern millipede.
Only two other fossils of this kind have been uncovered before, however, this fossil is the largest and the oldest yet.
The creature dates back to the Carboniferous Period, more than 100 million years before the Age of Dinosaurs.
Back then, the UK's landmass could be found near the equator, where Arthropleura would have roamed for 45 million years before becoming extinct.
Their extinction is possibly linked to global warming or due to the being out-competed for food after the rise of reptiles.
Where is the fossil now?
Cambridge's Sedgwick Museum willy display the fossil in the New Year.
The results of the study are reported in the Journal of the Geological Society.