After an incredible 115 years together, two giant tortoises at an Austrian zoo have gone their separate ways - refusing to share a cage any longer.The falling out, which has baffled zoo officials, marks the end of the world's oldest animal "marriage"."We get the feeling they can't stand the sight of each other any more," Zoo boss Helga Happ said.Bibi and Poldi have happily rubbed along at the Austrian zoo in Klagenfurt for 36 years, having moved together from Basel zoo in Switzerland.Both 115 years old, the pair grew up together - and eventually became an item.Zoo officials are not clear why the tortoises have fallen out but say Bibi, the female, started attacking her partner, biting off part of his shell."For no reason that anyone can discover, they seem to have fallen out. They just can't stand each other," Ms Happ said.Staff at the zoo realised all was not well when Bibi attacked Poldi, biting off a chunk of his shell. She launched further attacks on her partner until he was moved to a different location.