"a height of around 2.80 meters and an estimated weight of 350-400 kg (Alvarenga & Höfling, 2003)"

Ha! I can see such a bird being used as an armored mount. Lightweight warhorses weigh about that much (see wiki entry for war horse). Those horses are only about 1.4 meters tall, though, and are herbivores. This prehistoric bird would probably eat those war horses.

Do not taunt happy-fun-chocobo. Kweh.

Thank you for providing me with this amusement!