Generally speaking, the animals alive today are mere shadows of their former selves – everything from worms to otters to penguins to sharks were bigger and meaner in the distant past. And birds were no exception, as newly-found fossils indicate. In a Crimean cave, palaeontologists have uncovered the bones of some of the most gigantic birds to have ever walked the Earth, that would have lived alongside early European humans.

Dated to between 1.5 and 2 million years old, the bird belongs to the species Pachystruthio dmanisensis. Judging by the hefty thigh bone, the researchers estimated that it would have stood at least 3.5 m (11.5 ft) tall, and weighed as much as 450 kg (992 lb). That makes it one of the largest birds to ever exist.

"This formidable weight is nearly double the largest moa, three times the largest living bird, the common ostrich, and nearly as much as an adult polar bear," says Nikita Zelenov, lead author of a study describing the discovery. "When I first felt the weight of the bird whose thigh bone I was holding in my hand, I thought it must be a Malagasy elephant bird fossil because no birds of this size have ever been reported from Europe. However, the structure of the bone unexpectedly told a different story."

The team found that the new bird's femur was longer and slimmer than those of elephant birds. Closer in shape to the modern ostrich, that suggests that it was a much faster runner than elephant birds, which weren't built for speed with their big and bulky frames. Its speediness was probably key to its survival, too – the bones were found alongside plenty of Pleistocene predators, like giant cheetahs, hyenas and saber-toothed cats.

But perhaps the most intriguing thing about the bird is where it was found. Previously, gigantic bird bones have only been found in the Southern Hemisphere – the moa in New Zealand, the elephant bird in Madagascar, and the dromornithids of Australia. Finding these fossils in Crimea indicates that giant, ancient birds were more widespread than we thought.

That's backed up by the fact that bones from the same species had previously been found in Dmansi, Georgia, but their importance had gone unnoticed and uninvestigated. Those bones appear to be older, suggesting that the birds made their way into the Crimea region through the Southern Caucasus and Turkey. It would have shared the area with the earliest European human ancestors, who may have hunted them for meat, bones and feathers.

The research was published in the Journal of Vertebrate Paleontology.