Psilopterus

The most recent systematic revision of Phorusrhacidae placed Psilopterus within the subfamily Psilopterinae, along with the genera Procariama and Paleopsilopterus, and divided Psilopterus into four species. is the smallest species of phorusrhacid, rivaled only by P. affinis. The species (and genera) is defined by the upper portion of a fused ankle and leg bone (the lectotype MLP-168 is a tarsometatarsus). Other material assigned the species includes additional leg bones that are probably from the same bird, and an almost complete skeleton (PUM-15.904) The material is from several sites in the Santa Cruz Formation in the Santa Cruz Province of Argentina dating to the Middle Miocene (Santacrucian). The most important diagnostic characteristics are a low skull and upper jaw (or maxilla; similar to the mesembriornithine phorusrhacids) • Psilopterus bachmanni (Moreno & Mercerat, 1891) • Patagornis bachmanni Moreno & Mercerat, 1891 • Psilopterus communis Moreno & Mercerat, 1891 • Psilopterus intermedius Moreno & Mercerat, 1891 • Phororhacos delicatus Amegino, 1891 Brodkorb considered Psilopterus minutus Amerghino, 1981 a separate species, but the incomplete foot bone (tarsometatarsus) is indistinguishable from P. bachmanni. is the most poorly known species of terror bird, represented only by part of a leg bone (tarsometatarsus, MACN-A-52-184) which indicates the bird was very close to P. bachmanni in size. P. affinis is one of several species known from fragmentary material found in 1899 in the Chubut Province of Argentina (Patagonia), in rocks which dated to the Middle to Late Oligocene (Deseadan). Brodkorb assigned the species to Andrewsornis in 1967, == Classification ==

When P. bachmanni was originally described in 1891, few other birds now known as Phorusrhacids were described, but when Moreno & Mercerat named the taxon, they assigned Psilopterus (then Patagornis) bachmanni to a group with Phorusrhacos, Mesembriornis, and Stereornis, though the latter is now seen as a synonym of Phorusrhacos, In 1927, Psilopterus was placed in its own family and subfamily, Psilopterinae, and later recognized as being in its own family sometimes grouped with other Phorusrhacids like Palaeopsilopterus and Procariama. though a 2024 study reclassified Procariama as a psilopterine. The following phylogenetic tree shows the internal relationships of Phorusrhacidae under the exclusion of Brontornis as published by Degrange and colleagues in 2015, which recovers Psilopterus as the only member of Psilopterinae as a sister clade to Mesembriornithinae. == Paleobiology ==

The strong morphological similarity between the claws of the predatory cariama and Psilopterus, both of which are sharp, curved, and laterally compressed, may indicate they were used to strike prey. Like modern seriemas, psilopterines like Psilopterus would have fed on smaller animals based on their osteological traits. It has been also suggested that, in contrast to the other larger terror birds, Psilopterus may have been able to fly, with body mass estimates and hind limb proportions of psilopterines being similar to those of certain birds like Psophia and Otis which often walk but are able to run and fly. It is likely that psilopterines would have more preferred to run than fly, and that they would have utilized flight to reach the treetops for nesting and protection against predators. == Paleoenvironment ==

Psilopterus bachmanni and lemoinei lived during the middle Miocene in the Santa Cruz Formation, which preserves mostly a coastal environment, but also forested and grassland regions. The area had little rainfall, so forests developed around lakes and rivers, giving Santa Cruz a diverse environment. During the Miocene, the climate was similar to those of the coasts of Chile with semi-temperate forests and oceanic winds. Grasslands began spreading into Argentina during the Miocene, though much of inner Patagonia was still arid with small rainforests in between. Monte Leon preserved more mudstone and estuarine sediments, but with a very similar fauna to the Santa Cruz Formation as the two formations had a direct transition. == References ==