Tail vertebrae of birds are fused to form

Tail vertebrae of flying birds have fused to form pygostyle that support tail feathers.In flying birds, last thoracic, lumbar, sacral and few caudal vertebrae are fused to form synsacrum .In mammals, the caudal vertebrae fused to form coccyx.In amphibians like frogs have urostyle is formed by the fusion of sacral vertebrae.