Terror birds, which lived during the Cenozoic era, were capable of running at impressive speeds, estimated to be around 30 to 40 miles per hour (48 to 64 kilometers per hour). Their long legs and powerful muscles made them efficient runners, allowing them to chase down prey. While exact speeds can vary based on species and individual characteristics, they were among the top terrestrial predators of their time.
Running birds e.g. Ostrich can run fast comparable to horse in a desert .
Cassowary, if he can break the terror bird's chest with his head crest or kick him in the face. Then yet again, the terror bird has a huge beak and if the cassowary charges, the terror bird can break his neck. Juvenile terror bird wins 7 out of 10 bouts.
Ostrich and Emu.
Ostrich
Gentoo Penguin
Any bird is technically a dinosaur and Terror birds were the most similar to the actual beast of the Mesazoic. The body and stance of all species of terror bird were extremely similar to the body structure of therapod dinosaurs. Terror Birds were also very fast runners just like modern Ostriches and just like their Dromaeosaur ancestors.
I posted in the related links box below an article on the terror bird.
The ostrich can run as fast as the horse, although it cannot fly.
Terror Bird
It is the Ostrich.
Ostriches and emus do not fly and run quite fast.
they can run super fast their the most fastest bird on the planet.