Gastornitides

The Gastornitides were a family of large, flightless birds that lived during the Paleocene and Eocene epochs, about 66 to 34 million years ago.
They are sometimes called "terror birds" because of their predatory habits and powerful beaks.
They were widespread across North America, Europe, and Asia, and probably occupied a variety of habitats, such as forests, grasslands, and wetlands.

The Gastornitides had long legs and necks, and small heads with hooked beaks.
They ranged in size from 1.5 to 3 meters tall, and weighed up to 300 kilograms.
They had no wings, but instead had reduced arm bones and large claws on their hands.
They had strong muscles in their legs and feet, which enabled them to run fast and kick their prey.
They also had a large, hollow keel on their breastbone, which may have been used for sound production or as a resonating chamber.

The Gastornitides were carnivorous or omnivorous, and fed on small to medium-sized mammals, reptiles, and other birds.
They may have hunted in packs or as solitary predators, using their speed and agility to chase down their prey.
They may have also scavenged on carcasses or used their beaks to dig up roots and tubers.
They had no teeth, but their beaks were sharp and serrated, and could inflict severe wounds on their victims.
They may have swallowed their prey whole or torn it apart with their beaks.

The Gastornitides became extinct by the end of the Eocene, possibly due to climate change, competition from other predators, or human hunting.
They left no living descendants, but they are related to modern waterfowl, such as ducks and geese.
They are also considered to be among the earliest and most successful examples of avian gigantism, a phenomenon that occurred several times in the history of birds.