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Psilopterus (Greek language for "bare wing") is an extinct genus of Phorusrhacidae ("terror bird") from the Middle Oligocene to possibly the Late Pleistocene of Argentina and Uruguay. Compared to other phorusrhacids, members of the genus are both relatively gracile and diminutive, and include the smallest known species of terror bird: with the head raised P. bachmanni was in height and weighed about , while the largest members of the genus were only about . The birds resemble the modern cariama ( Cariama cristata), except with a heavier build and considerably smaller wings. Fossil finds in Uruguay indicate the genus may have survived until 96,040 ± 6,300 years ago, millions of years after the larger phorusrhacids became extinct.
Junior synonym:Per Alvarenga & Höfling (2003), who rely on Brodkorb (1967).
Synonyms:
Psilopterus affinus
Psilopterus affinus (Ameghino, 1899) 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. affinus 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). Additional specimens might help clarify the taxonomy of the four apparently unrelated species. P. affinus was originally assigned to the genus Phororhacos despite the difference in size, and is distinguished from P. bachmanni by a groove on the leg bone. Bertelli et al. kept this species in Phororhacos. Taxonomic opinions tied to S. Bertelli et al. 2007 at Fossilworks.org Brodkorb assigned the species to Andrewsornis in 1967, but this is no longer considered accurate.
Psilopterus colzecus
The most recently discovered species in the genus, Psilopterus colzecus Tonni & Tambussi, 1988, is similar to P. lemoinei in size. Known only from a single incomplete skeleton that includes parts of the jaw, arm, and leg (holotype MLP-76-VI-12-2), the species is defined by a groove in the front of the thigh bone (Femur). The elements were found in the Arroyo Chasicó Formation in Buenos Aires Province of Argentina and are dated to the Late Miocene (Chasicoan).
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,Brodkorb, P. (1967). Catalogue of fossil birds: part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). University of Florida. that they named Stereornithidae. Since then, Psilopterus was considered the ancestor of larger Phorusrhacids like Mesembriornis and the modern Cariama.Rovereto, C. (1914). Los estratos araucanos y sus fósiles. An. del Mus. Nac. Hist. Nat. Buenos Aires, 25. In 1927, Psilopterus was placed in its own family and subfamily, Psilopterinae,Dolgopol de Saez, M. (1927). Las aves corredoras fósiles del Santacrucense. In Anales de la Sociedad Científica Argentina (Vol. 103, pp. 145-64). and later recognized as being in its own family sometimes grouped with other Phorusrhacids like Paleopsilopterus and Procariama. However, in the phylogenetic analysis by Degrange et al. (2015), Psilopterus was found as the only psilopterine, though a 2024 study reclassified Procariama as a psilopterine. Supplementary Information 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 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, probably in a brief and clumsy manner like that of extant seriemas, (2025). 9780521194617, Cambridge University Press. ISBN 9780521194617 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. Large, herbivorous, South American Notoungulata mammals like the Toxodontidae Nesodon and Adinotherium were the large low browsers, with rabbit-like Interatheriidae Protypotherium being Frugivore. Both mammalian and avian carnivores inhabited the area, the largest being the phorusrhacid Phorusrhacos. also lived in the region, including the large carnivorous Sparassodonta Borhyaena. Psilopterus lemoinei is also known from the coastal Monte Leon Formation that was in the same region in Santa Cruz, but part of the older Early Miocene age. Monte Leon preserved more mudstone and Estuary sediments, but with a very similar fauna to the Santa Cruz Formation as the two formations had a direct transition.
External links
Categories: Phorusrhacidae, Extinct Flightless Birds, Oligocene Birds, Paleogene Birds Of South America, Miocene Birds Of South America, Deseadan, Santacrucian, Chasicoan, Huayquerian, Montehermosan, Oligocene Argentina, Pleistocene Argentina, Fossils Of Argentina, Oligocene Uruguay, Pleistocene Uruguay, Fossils Of Uruguay, Fossil Taxa Described In 1891
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