Teratornis

T. merriami skeleton from the La Brea tar pits in flight pose

• Teratornis merriami.[1] This is by far the best-known and most commonly found species. Up to a hundred specimens have been found, mostly from the La Brea Tar Pits. It stood about 75 cm (29.5 in) tall with estimated wingspan of perhaps 3.5 to 3.8 metres (11.5 to 12.5 ft), and its weight has been estimated within the range of 12.5–15.0 kilograms (27.6–33.1 lb) with 95% confidence; making it about a third bigger than extant condors. It became extinct at the very end of the Pleistocene, some 10,000 years ago. Before the formation of the Teratornithidae family, The T. merriami's hooked beak and skull morphology led to its initial placement in the family Vulturidae alongside New World Vultures. Further analysis has suggested a potentially equal relation to storks in the Ciconiidae family. Despite similarities, these three families can be differentiated by their differing skulls in response to significantly different feeding methods.[3]
• Teratornis woodburnensis.[4] The first species to be found north of the La Brea Tar Pits, this partial specimen was discovered at Legion Park, Woodburn, Oregon in 1999. It is known from a humerus, parts of the cranium, beak, sternum, and vertebrae which indicate an estimated wingspan of over 4 meters (14 ft).[5] The find dates to the late Pleistocene, about 12,000 years ago, in a stratum containing the remains of megafauna such as mammoth, mastodon, and ground sloths, as well as evidence of early human occupancy at the site.[4]

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.[6]

A closely related genus, Aiolornis, was about 40% larger and lived at an earlier time; it was formerly known as Teratornis incredibilis, but is distinct enough to be placed in its own genus.

Reconstructed skull

According to description of 1945, Teratornis merriami had a wingspan of around 3.5 to 3.8 m (11 to 12 ft) and a wing area of 17.5 square meters, standing an estimated 75 cm (30 in) tall. It was somewhat larger than the extant Andean condor, and by calculating the area of the organism's sternum and synsacrum, Teratornis was estimated to weigh about 22.5 kg (50 lb), which was nearly double the weight of an average Californian condor.[7] A 1983 study gives a range of wingspan of 2.938–3.379 m (9.64–11.09 ft) and a weight of 13.7 kg (30 lb).[8]

The finger bones of the Teratornis were fused as in all modern birds; however, part of the index finger forms a shelf which aided in bearing the load of long and stout primaries, enabling the bird to utilize strong upcurrents in flight. Their legs were similar to an Andean condor's, but stouter, and the feet could hold prey for tearing off pieces, but could not exert a very forceful grip like birds of prey. Its wing loading was not much larger than a Californian condor's, and Merriam's teratorn should have been able to take off by simply jumping and beating its wings under most circumstances.[6] Indeed, it seems to have been better adapted for utilizing a short run into the wind from an elevated location as condors do, as its legs are proportionally smaller and its stride less than in condors.[9] Thus, Teratornis may have primarily inhabited cliff terrain, where it could take off and soar through the air easily. [7]