Giant prehistoric 'terror bird' once thought to be a ruthless predator was actually a VEGETARIAN The two-metre gastornis was a flightless creature that lived in Europe between 40 and 55 million years ago Because of its size and fearsome appearance, paleontologists believed the creature was a top carnivore that used it beak to break its prey's neck But analysis of its bones has revealed that its diet was probably plant-rich A giant prehistoric "terror bird" - once thought to have been a ruthless predator which snapped the necks of mammals with its enormous beak - was actually a vegetarian, according to a new study. The two-metre gastornis was a flightless creature which lived in Europe between 40 and 55 million years ago. Because of its size and ominous appearance, it was thought to be a top carnivore, the Goldschmidt conference in Florence was told. Dr Thomas Tütken (right), from the University of Bonn, said: 'The 'terror bird' was thought to have used its huge beak to grab and break the neck of its prey.' The fossilised remains of the Gastornis (mock-up pictured left) that were studied were found in a former open cast coal mine But now a team of German researchers, who studied fossilised remains of the beasts found in a former open cast coal mine, say they believe it was actually not a meat eater. Dr Thomas Tütken, of the University of Bonn, said: 'The terror bird was thought to have used its huge beak to grab and break the neck of its prey, which is supported by biomechanical modelling of its bite force. It lived after the dinosaurs became extinct and at a time when mammals were at an early stage of evolution and relatively small; thus, the terror bird was though to have been a top predator at that time on land. But recent research cast doubt on its fearsome reputation. Palaeontologists in the U.S. found footprints believed to belong to the American cousin of gastornis, and these do not show the imprints of sharp claws, used to grapple prey, that might be expected of a raptor. Palaeontologists in the U.S. found footprints believed to belong to the American cousin of gastornis (gastornis pictured), and these do not show the imprints of sharp claws used to grapple prey, that might be expected of a raptor Some paleontologists even suggested the gastornis hunted small horses (mock-up pictured). The reality is that it was probably far too heavy to chase such mammals and instead lived off a diet of plants and maybe nuts and seeds Also, the bird's sheer size and inability to move fast made some believe it couldn't have preyed on early mammals - though others claim it might have ambushed them. The gastornis was around two metres tall and weight several hundred pounds. It was named after Gaston Planté who found the first remains. The bird was one of the largest animals alive during the late Paleocene-Middle Eocene period. Until now many experts believed that the creature was a silent ambush hunter in the thick forests that ate prey such as small horses. gastornis fossils are common at the Geiseltal site in Germany, and in the USA. Dr Tütken and his colleagues took a new approach to determine the diet of gastornis, and by analysing the calcium isotope composition in fossilised bones, they were able to identify what proportion of the creature's diet was plant or animal, and its position in the food chain. This relies on the calcium isotope becoming lighter as it passes through the food chain. Scientists analysed the isotopes of known predators, including T-Rex, herbivores, and mammals living today. They then compared these to those of the terror bird. Their results showed that the calcium isotope compositions of terror bird bones are similar to those of herbivorous mammals and dinosaurs and not carnivorous ones. But researchers want to cross check their data using other fossil assemblages before confirming their findings. The creature was thought to a feasome animal than used its beak to maul prey and fight off competition (mock-up pictured). The gastornis lived after the dinosaurs became extinct and at a time when mammals were at an early stage of evolution Dr Tütken and his colleagues took a new approach to determine the diet of gastornis (pictured), and by analysing the calcium isotope composition in fossilised bones, they were able to identify what proportion of the creature¿s diet was plant or animal, and its position in the food chain. Dr Tütken said: "Tooth enamel preserves original geochemical signatures much better than bone, but since gastornis didn't have any teeth, we've had to work with their bones to do our calcium isotope assay. Because calcium is a major proportion of bone - around 40% by weight - its composition is unlikely to have been affected much by fossilisation. However, we want to be absolutely confident in our findings by analysing known herbivores and carnivores using fossilised bone from the same site and the same time period. This will give us an appropriate reference frame for the terror bird values.