Physornis is an extinct genus of giant flightless of the family Phorusrhacidae or "terror birds", most closely related to Paraphysornis, that lived in Argentina. The type species is P. fortis. It lived during the Oligocene (Deseadan). Few fossils are known, but the available material suggests that Physornis was one of the largest phorusrhacids.
History and taxonomy
The
holotype of
Physornis (BMNH-A583) is a 137 mm long portion of a symphysis and the right branch of this lower jaw, described in 1894 by paleontologist Florentino Ameghino. He published the name, together with a description but without a drawing, in the same year.
[Brodkorb, P. (1967). Catalogue of fossil birds: part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). University of Florida.][Alvarenga, H. M., & Höfling, E. (2003). Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Papéis Avulsos de Zoologia, 43(4), 55-91.] The fossil was collected from the
Oligocene layers of Santa Cruz Province,
Argentina and the
Deseadan era
SALMA, making it one of the older known phorusrhacid species.
The type specimen of
Physornis fortis is very fragmetary and besides the type symphysis has virtually no other characteristics, and this has caused the validity of the species to come into question.
[Patterson, B. (1941). A new phororhacoid bird from the Deseado formation of Patagonia.] and paleontologist Bryan Patterson suggested that the type specimen could be from the pelvis of a mammal, claiming that it is a
nomen dubium.
However in 2003 during their review of phorusrhacidae, Herculano Alvarenga and Elizabeth Höfling found the type symphysis to be diagnostic and from a large phorusrhacid similar to
Paraphysornis and
Brontornis,
though the latter has since been suggested to be a
Galliformes.
[Agnolin, F. L. (2021). Reappraisal on the Phylogenetic Relationships of the Enigmatic Flightless Bird (Brontornis burmeisteri) Moreno and Mercerat, 1891. Diversity, 13(2), 90.]
Florentino Ameghino named another genus and species of phorusrhacid in 1898, Aucornis eurhynchus, based on a partial mandibular symphysis, proximal tarsometatarsus, and 3 Phalanx bone recovered from the "cretaceo de Patagonia", though these fossils most likely date to the Oligocene instead.
In 1982, Herculano Alvarenga named a new species of Physornis, Physornis brasiliensis, based on a 75% complete skeleton from the Upper Oligocene - Early Miocene layers of São Paulo, Brazil.[Alvarenga, H.M.F. (1982). "Uma gigantesca ave fóssil do cenozóico brasileiro: Physornis brasiliensissp. n." Anais da Academia Brasileira de Ciências. 54 (4): 697–712.] A decade later in 1993, Alvarenga came to the conclusion that it was actually its own genus of Phorusrhacid that he named Paraphysornis.[Alvarenga, H.M.F. (1993). "Paraphysornis Novo Gênero Para Physornis brasiliensis Alvarenga, 1982 (Aves:Phorusrhacidae)". Anais da Academia Brasileira de Ciências. 65 (4): 403–406.]
Description
Physornis has been referred to the Brontornithinae subfamily, the largest and most solidest shock birds, though
Brontornis itself is likely not a Phorusrhacid.
Physornis probably had a huge size, possibly even approaching to that of
Brontornis. The Symphysis Mandibulae is remarkably short and wide and has a characteristic ventral surface in the middle section. The lateral edge of the Hypotarsus is, seen from behind, an excellent comb that clearly distinguishes the genus
Paraphysornis and
Brontornis.
The lateral cotyle of the
tarsometatarsus is almost square when it is seen from close by.
Classification
Ameghino originally classified
Physornis with his taxa
Phorusrhacos and
Patagornis, though in years since it has also been classified closest to
Brontornis and
Paraphysornis, the former possibly being a type of
gastornithid or
Anseriformes instead.
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
Physornis as a member of a large clade that includes
Patagornis,
Phorusrhacos and
Andalgalornis, among others.
