Dating site niches
There were some suggestions that phorusracids, like the majority of Pleistocene megafauna, were killed off by human activity such as hunting or habitat change.This idea is no longer considered valid, as improved dating on Titanis specimens show that the last phorusracids went extinct over one million years before humans arrived.Most species described as phorusrhacid birds were smaller, 60–90 cm (2.0–3.0 ft) tall, but the new fossil belongs to a bird that probably stood about 3 m (9.8 ft) tall.Scientists theorize that the large terror birds were extremely nimble and quick runners, able to reach speeds of 48 km/h (30 mph).It has been recently shown that at least some phorusrhacids like Andalgalornis, while very fast runners in a straight line, were poor at tight turns at speed, which contradicts the idea of phorusrhacids being agile predators of small prey.All phorusrhacids are thought to have been carnivorous.
However, even with these attributes, the phorusrhacids are often assumed to have preyed on relatively small animals (about the size of a rabbit) that could be dispatched with a minimum of struggle.
However, fossil finds in South America dating to the late Pleistocene indicate that Psilopterus, a relatively small form, may have been present until 96,040 ± 6300 years ago.
If true, this extends the existence of this group of avian predators considerably.
Once stretched out into its full length in preparation for a downward strike, its developed neck muscles and heavy head can produce enough momentum and power to cause fatal damage to the terror bird’s prey.
Kelenken guillermoi, from the Langhian stage of the Miocene epoch, some 15 million years ago, discovered in Patagonia in 2006, represents the largest bird skull yet found.