Temporal range: Miocene
An artist's illustration of Brontornis burmeisteri as a phorusrhacid.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Infraclass: Paleognathae
Genus: Brontornis
Moreno & Mercerat, 1891
Species: B. burmeisteri
Binomial name
Brontornis burmeisteri
Moreno & Mercerat, 1891
  • Rostrornis Moreno & Mercerat, 1891

Brontornis was a genus of giant flightless predatory birds that lived in Patagonia. The only species currently accepted as valid is B. burmeisteri. Although traditionally placed in the family Phorusrhacidae, nicknamed "Terror Birds" for their large size and predatory lifestyle, the true taxonomic position of Brontornis is highly unclear, usually being placed in the Cariamiformes clade of birds which includes the aforementioned terror birds or in the Anserimorphae clade which includes Gastornithids and Dromornithids (mihirungs). It is known from bones, mainly of the legs and feet but also some skull and backbone parts, found in several localities of Santa Cruz Province.

If the claim that B. burmeisteri belongs to Phorusrhacidae is valid, then that would mean it is the second largest phorusrhacid known, with a height of around 2.8 meters (9.2 feet) and an estimated weight of 350–400 kilograms, making it the third-heaviest bird ever according to current knowledge (after Aepyornis maximus and Dromornis stirtoni), and the most massive land predator of its time and place. In attacking prey (but probably not necessarily in a defensive situation, as it was too slow-moving) it most likely was the dominant carnivore of Miocene Patagonia, being able to kill even large animals such as the elephant-like Astrapotherium and in the predatory role being on par with a pack of Thylacosmilus (metatherian sabre-tooth). It coexisted with some slightly smaller and more active phorusrhacids like Phorusrhacos, but apparently became extinct before the appearance of the immense Argentavis, the largest flying bird ever. However, if B. burmeisteri was a gastornithiform instead, then it may have sustained its large size through feeding on vegetation as its beak was found to most likely be unsustainable for tearing animal food, instead appearing to be adapted for a herbivorous lifestyle. Likewise, the feet of B. burmeisteri were also found to be incapable of housing raptor-like claws, supporting the claim of a more plant-based diet.


There are several synonyms of the species and genus:

  • Rostrornis floweri (Moreno & Mercerat, 1891)
  • Brontornis platyonyx (Ameghino, 1895)

Possibly, the fossils described as B. platyonyx represent another species; they are about one-third smaller than the largest Brontornis bones. It is speculated, however, that they might have represent sexual dimorphism. In today's hawks and owls, females are, usually, considerably larger than the males; this prevents overutilization of one size class of prey. It is not known whether phorusrhacid males or females would have been larger, but the fossils of the North American phorusrhacid Titanis also show considerable variation in size, suggesting that there was indeed at least a tendency for differently-sized sexes, albeit it is unclear which.

Brontornis VS Hadrosaur

A highly anachronistic and outdated paleo - restoration of a Brontornis that is being attacked by a hadrosaur, 1902-1906

The taxonomic position of Brontornis is highly debated, as while it is traditionally placed under the Phorusrhacidae family, more recent studies claim that it is actually an anseriform. The other genera traditionally assigned to the subfamily Brontornithinae (Physornis and Paraphysornis) apparently are true phorusrhacids, so the subfamily containing them had been proposed to be renamed Physornithinae, with Physornis fortis as the type. If valid, this would mean that there are three groups of giant basal anseriforms, in chronological order of divergence first the Gastornithids (relatives of Gastornis) then Brontornis and finally the mihirungs of Australia. However, a subsequent analysis interprets Brontornis as having adaptations to great weight but exhibiting diagnostic thoracic vertebrae, putting it back squarely within the phorusrhacids. A later study from 2017 then suggests the placement of Brontornis to be in the order Cariamiformes, but not directly within Phorusrhacidae, pointing out that previous studies used the more fragmentary material of the species. Another study from 2021 places Brontornis within the Anseriformes again, specifically as a Gastornithiform — the group that includes Gastornithids and mihirungs.