Terratornis was a genus of huge North American birds of prey.

Taxonomy:
1) Teratornis merriami: Because of the numbers foud at Rancho La Brae and the tar pits, is is by far the most researched species. Over a hundred specimens have been found. It stood about almost 30inches (or 75cm) tall with estimated wingspan of almost 3.8 metres (11.5 to 12.5 ft). Its weight has been estimated at 10 to 15 kilos.
2) Teratornis woodburnensis: In 1999, at Legion Park, Woodburn, Oregon. Parts of the teratornis woodburnesis were found. There was a humerus,
parts of the cranium, beak, sternum, and vertebrae. Scientists were able to estimate a wingspan of over 4 meters (14 ft). The find dated
to about 12,000 years ago, during the late pleistocene. In combination with this ‘wonder bird’ find. A stratum containing remains of megafauna such as mammoth, mastodon, ground sloths, and early human occupantion was discovered at the site.
3) Another form, “Teratornis” olsoni, was described from the Pleistocene of Cuba, but its affinities are not completely resolved; it might not be a teratorn, but has also been placed in its own genus, Oscaravis. There are also undescribed fossils from southwestern Ecuador, but apart from these forms, teratorns were restricted to North America.

Even when as large as these 4 meter wing spans (almost 15 feet). Bird fossils are very hard to find. It took ten thousand years for scientists to identify the hundreds of teratornis fossils mostly from California, Oregon, southern Nevada, Arizona, and Florida.

Description
As in all modern birds, finger bones of ‘wonder birds’ were fused. Though, part of there index finger formed a shelf. It aided in hard take offs, and not when availably enabled to utilize drafts of strong upcurrents. Their legs were strong, there feet could hold prey and tear off pieces. Though, its believed there short length was not quite as forceful as some other birds of prey. Teratorns (or ‘wonder birds’) should have been able to take off by simply jumping and beating there wings. Because its legs were smaller, it seems to have been batter adapted for utilizing a short run into the wind, or off a large tree, ledge or cliff, as some other height point like birds do. They probably inhabited cliffs and rugged terrain, where they could take off and soar through the air easily.

Paleobiology, Diet and Feeding Habits
Analysis of functional morphology of skull, its larger bill and ability to spread its mandibles and swallow its prey whole. Suggest it was an active and carnivorous predator rather than a scavenger. Similar to condors. Other viewpoints note that like many old world vultures that possess large bills. It allowed them to probe deeper into large carcasses.
Small and sideward facing eyes and there low skull are also consistent with a scavenging lifestyle. For these crazy birds, small prey such as
frogs, lizards, snakes, young birds, and rodents were swallowed whole. Larger mammels or carion would have been fed on similar to condors or
vultures.

Locomotion
An analysis of the teratornis pelvic area and stout; and, columnar hind leg bones suggests that its legs had greater anteroposterior ability than condors. And, that they were agily, well-suited for walking and stalking prey on the ground. More similarl to storks and turkeys.
Opposite, their flight was similar to that of condors. The large condor birds fly by means of soaring on rising up-currents. Generally weak currents are subject to sudden changes in strength and direction. Their ability to react to these, sometimes sudden current changes, and maintain flight is essential. Contrary to some other birds who rely more on current. There ability to deal with wind, draft, and current changes. Has to do with their emarginated primary feathers. Which can separate, adapt and move independently during flight. Because of there size, they needed it.

Habitat
Wonderbirds legs are quite short for it to take flight by just running on flat ground like some birds do. Because of this it has been hypothisied teratornis started at heights where it could take off, flap its large wings a few times, and soar through the air easily.
These birds were thought to have been attracted to tar pits by struggling Pleistocene megafauna. Cats, mammoth, sloth and other fauna were attracted to the water that would pool on top of the tar. The teratorns sometimes would fight, or struggle with they megafauna and fall victim to the sludgy deposits. Yikes.
At the tar or sludge deposits, vultures and other birds were also present. Teratornis would have been also adapted to hunt for smaller animals which also would had been around the pools.

Like eagles, skull and bill shape analysis identifys that fish may have also constituted a large portion of the ‘wonder birds’ diet. Though not quite as developed as an eagles legs. Fish are slippery and can be large. They had strong legs, stout claws, and gripping power. Its more likely they hunted like osprey, which also explains why it was significant at Rancho La Brae. They were probably fighting or struggling with pleistocene megafauna, as well as other birds.

Perhaps the Teratornis or ‘wonder bird’, are what some native Americans, aboriginals, and people spoke of mythologically. And, about a thunder-bird. No matter what the cause these were some big birds. Lets hear it for the giant north American bird of prey. Teratornis’s. Your wonder bird.

Bibliography: Miller, Loye H. (1909). “Teratornis, a new avian genus from Rancho La Brea”. University of California Publications, Bulletin of the Department of Geology. 5: 305–317.

Campbell, Kenneth; Tonni, Eduardo (18 October 1982). “Size and Locomotion in Teratorns (Aves: Teratornithidae)” (PDF). Natural History Museum of Los Angeles County: 390–403.