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 Tolmodus, though in years since it has also been classified closest to Brontornis and Paraphysornis, the former possibly being a type of gastornithid or Anseriform 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. References Brontornithinae Deseadan Fossils of Argentina Fossil taxa described in 1895 Taxa named by Florentino Ameghino Phorusrhacidae Oligocene birds Golfo San Jorge Basin Sarmiento Formation