Savage Earth: Cold Moon
Phorusrhacids (“Rag-Thieves”), or terror birds, are a family of large carnivorous flightless birds which are the dominant predators in Central American jungles. they stand between 1–3 meters (3–10 feet) tall (the given stats are for the larger varieties).
Larger speceis of the terror birds can easily crush the skull of its prey and puncture through bone with its beak. Armed with a fearsome weapon, a beak which could be driven into prey with the force of a sledgehammer, and their ability to run at high speeds over long distances these larger species are apex predators in regions with no Dinosaurs.
whil;e it is possible to ride these creatures, they cannot be tamed without magical means and no amount of mundane skill will allow a hominid to mount one or use it for manual labour.