[7] It was once believed that T. walleri became extinct in North America around the time of the arrival of humans,[8] but subsequent datings of Titanis fossils provided no evidence for their survival after 1.8 Ma.

[9] However, reports from Uruguay of new findings of phorusrachids such as a specimen of Psilopterus dating to 96,040 ± 6,300 years ago would imply that phorusrhacids survived in South America until the late Pleistocene.

[12][13][14] Possible specimens have also been discovered from the La Meseta Formation of Seymour Island, Antarctica, suggesting that this group had a wider geographical range in the Paleogene.

[16][17] At least one analysis recovers Bathornis as sister taxa to phorusrhacids, on the basis of shared features in the jaws and coracoid,[18] though this has been seriously contested, as these might have evolved independently for the same carnivorous, flightless lifestyle.

This suggests that the phorusrhacid had a highly flexible and developed neck allowing it to carry its heavy head and strike with terrifying speed and power.

Once stretched out into its full length in preparation for a downward strike, its developed neck muscles and heavy head could produce enough momentum and power to cause fatal damage to the terror bird's prey.

[20] Kelenken guillermoi, from the Langhian stage of the Miocene epoch, some 15 million years ago, discovered in the Collón Curá Formation in Patagonia in 2006, represents the largest bird skull yet found.

The second toe, which was shorter and had fewer phalanges, also had more resistance and would make it easier to hold the claw off the ground and retain prey, a compromise with its predatory function and movement on the run, as occurs with modern seriemas, although to a lesser degree of specialization than dromaeosaurid dinosaurs.

The strong downwards curve from the tip of this beak suggests that it ripped the flesh from the body of other animals; many extant bird species with this feature are carnivorous.

[31] Florentino Ameghino claimed in a letter to Édouard Trouessart that he had specimens from Argentina of "petrified masses preserving skeletons of large rodents, Interatheriidae [small notoungulates] and even Proterotheriidae [deer-sized litopterns], with all their bones crushed and corroded, piled on with no apparent order and forming a nearly spherical mass with the skull in the center" that resembled giant owl pellets, suggesting that phorusrhacids may have swallowed their prey whole and regurgitated the indigestible parts similar to owls.

Current thinking is that the name is derived from a combination of the Greek words "phoros", which means bearer or bearing, and "rhakos", which translates to wrinkles, scars or rents.

During the early Cenozoic, after the extinction of the non-bird dinosaurs, mammals underwent an evolutionary diversification, and some bird groups around the world developed a tendency towards gigantism; this included the Gastornithidae, the Dromornithidae, the Palaeognathae, and the Phorusrhacidae.

[41] The following classification is based on LaBarge, Garderner & Organ (2024), and taxa identified as incertae sedis were all excluded from phylogenetic analysis in their study (except for Brontornis):[14] Family Phorusrhacidae Alvarenga and Höfling did not include the Ameghinornithidae from Europe in the phorusrhacoids; these have meanwhile turned out to be more basal members of Cariamae.

[57] Bathornithids, which were similar in ecology and are likely close relatives of phorusrhacids, existed entirely within North America during part of the Cenozoic and competed successfully for a time with large carnivorans such as nimravids,[17] before becoming extinct in the Early Miocene, about 20 million years ago.

This idea is no longer considered valid, as improved dating on Titanis specimens show that the last phorusrhacids went extinct over one million years before humans arrived.

Psilopterus may have been present until 96,040 ± 6,300 years ago (maximum age obtained from the bottom of the fossil-containing stratum), which would extend the existence of the smaller members of this group of avian predators considerably.