What was a kelenken?

The kelenken was a massive predatory bird, with a skull about 71.6 cm (28.2 in) long, the longest head if any known bird. It is a genus of Phorusrhacid ("terror bird"), an extinct group of large, predatory birds, which lived in what is now Argentina in the middle Miocene about 15 million years ago. The only known specimen was discovered by high school student Guillermo Aguirre-Zabala in Comallo, in the region of Patagonia, and was made the holotype of the new genus and species Kelenken guillermoi in 2007. The genus name references a spirit in Tehuelche mythology, and the specific name honors the discoverer.

Phorusrhacids were large, flightless birds with long hind limbs, narrow pelvises, proportionally small wings, and huge skulls, with a tall, long, sideways compressed hooked beak. Kelenken is the largest-known phorusrhacid, 10% larger than its largest relatives known previously. At 716 mm (2.3 ft) long, the holotype skull is the largest known of any bird, and has been likened to the size of a horse's skull. The tarsometatarsus leg bone is 437 mm (17 in) long. Kelenken is thought to have been about 3 m (9.8 ft) tall and exceeded 100 kg (220 lb) in weight.