Phorusrhacos, the "Rag-Thief" or "Wrinkle Bearer," is a "terror bird" that is only known from partial fossils. Its approximate size is estimated to be two and a half  meters tall, since with only fragmentary evidence its size cannot be said for certain. The meaning of  its name describes the "wrinkled"  curve of its lower jaw. Like other  terror birds, it had a massive hooked beak that was built for  consuming meat. How it hunted is unknown, but it almost certainly feasted on small mammals. It may  have used its beak or sharp claws to deal blows on their unfortunate prey, or repeatedly beat their poor victims against the ground like  their modern relatives seriemas.  During the start of its reign in Miocene Argentina, Phorusrhacos ruled grasslands and woodlands,  stalking around in the search for  food around the hills that would eventually become the Andes  Mountains. It lived alongside four  other terror birds, so they must  have evolved to hunt different prey  - otherwise, they undoubtedly would have fought with one another.  Although a fearsome predator, the Phorusrhacos went extinct before  the Miocene Epoch ended, and at present it is not known why. Until further research is done or new  fossils are discovered, it will  continue to be another mystery paleontology is working to solve.