The Lost Universe: Ancient Giant Terrestrial Birds Part 3 - Giant Phorusrhacids

The Gastornithids introduced in the previous article had strong herbivorous tendencies and are believed to have rarely actively attacked other animals. However, among ancient terrestrial birds, there were also agile and powerful, terrifying predators.
The majestic figure of the 'Phorusrhacids,' which ran across the ground at incredible speeds and finished off prey with sharp beaks and claws, overlaps with their ancestors, the carnivorous dinosaurs. I would like to explore the true nature of these most fearsome birds that made the mammals of the time tremble, while deciphering cutting-edge research.

Who were the Phorusrhacids?

The 'Terror Birds' that excelled in speed and attack power

|Terror Birds|. Also known as Terror Birds. If you are well-versed in paleontology, you may recognize the name.
Terrestrial birds that flourished in the Cenozoic era acquired forms and ecologies that closely resembled their ancestors, the |theropods|. They are the terror birds, a group of predators representing the Cenozoic era. Note that the term 'terror bird' is merely a common name and not an official taxonomic group name.

The species that made a name for themselves in the Cenozoic era as carnivorous terrestrial birds are the group of terror birds called 'Phorusrhacids.' This taxon has strong carnivorous tendencies and is a cursorial hunter that catches prey by running at high speeds. Most Phorusrhacid fossils have been discovered on the South American continent, and it has been determined that they flourished for a long period from about 43 million to about 25,000 years ago (Middle Eocene to Late Pleistocene). If we include somewhat dubious fossil specimens of uncertain classification, the production age of the oldest species dates back to about 53 million years ago (Early Eocene), and the newest species may have lived about 18,000 years ago (Late Pleistocene).
Large Phorusrhacids reached a height of about 3 m from the ground to their heads and flourished while more than adequately competing with large carnivores such as saber-toothed tigers. In terms of mobility and attack power, they were no less capable than carnivorous mammals, and Phorusrhacids were likely the apex predators of the South American continent.

Speed and attack power are top-notch. Research results have been published stating that Phorusrhacids could run at 50 km/h, and once they found you, it was the end; unless you were a very fast animal, you could not escape. Their powerful leg strength was likely also utilized during hunting.
The claws on the legs of the current terrestrial bird, the cassowary, are extremely sharp, and they slash the bodies of natural enemies with a lethal kick. The kicks of the much larger, giant Phorusrhacids likely dealt massive damage even to large animals. Their powerful legs were not only useful for delivering slashes but also for pinning down prey.

The beak bones of Phorusrhacids were strongly fused and structurally excellent for vertical movement, so they were likely good at pecking attacks. Depending on the situation, they probably used them in conjunction with kicks to inflict tremendous impact and slashes on their prey. Equipped with lethal weapons and sprinting across the ground at high speeds, Phorusrhacids possessed combat power befitting an apex predator in the ecosystem.

Terror birds are powerful terrestrial hunters. Which species of living birds are they phylogenetically close to? Actually, the close relatives of the Phorusrhacids are a quite unexpected group.

The evolution of Phorusrhacids, the path of kings

Among the Phorusrhacid fossil specimens discovered so far, there are skeletons in good states of preservation, as well as fragmentary specimens that are doubtful as to whether they are truly Phorusrhacids. In current paleontology, the specimen considered the oldest certain Phorusrhacid is a part of a hind limb bone unearthed in Argentina about 43 million years ago (Middle Eocene). Although there are many mysteries regarding their origins, the evolutionary lineage of Phorusrhacids is gradually becoming clear through extensive investigation and research.
Actually, Phorusrhacids are closely related to the living seriemas, and the family Phorusrhacidae is included in the group called 'Cariamiformes.' Although living seriemas have the ability to fly, they have the habit of running around on the ground to hunt, and their ecological behavior is reminiscent of Phorusrhacids.

In a broad sense, seriemas are closely related to falcons and passerines. There were multiple groups in the order Cariamiformes, including the family Phorusrhacidae, but many species went extinct in the course of evolutionary history, and only one lineage, the family Cariamidae, exists today.
As mentioned above, Phorusrhacids continued to flourish for a long time until the end of the Cenozoic era. Even when carnivorous mammals such as saber-toothed tigers appeared on the South American continent, the Phorusrhacidae stood their ground and continued to stand at the top of the ecosystem without taking a single step back. The decline of Phorusrhacids was by no means a survival competition with other animal species, but is thought to have been due to complex environmental factors, and it seems that more investigation and research will be needed.

Living up to their name as 'terror birds' and displaying even more ferocity, the Phorusrhacids roamed the earth with power.Much like the Tyrannosaurus of the past, these giant flightless birds reigned at the top of the ecosystem. What kind of giant birds were the large species of this group—the toughest of the tough?

Giant Phorusrhacids

Devincenzia: A Heavyweight Terror Bird That Hunted Terrestrial Animals with Overwhelming Power

Broadly speaking, there are two types of Phorusrhacid skulls: those with primitive traits and those equipped with sturdy, powerful beaks. The latter characteristic is frequently observed in large species, and it is notably present in the genus Devincenzia, discovered in Argentina and Uruguay.
Devincenzia is thought to have flourished over a long period from the early Miocene to the early Pliocene, and there are even reports of fossils of this genus being found in early Pleistocene strata. Integrating the above information, it seems that the glory of Devincenzia continued in South America for at least about 23 million to about 5 million years ago (could they have lived in times more recent than about 2.58 million years ago?).Even in an era when mammals were evolving rapidly, the Phorusrhacids brilliantly maintained their position as top predators in the ecosystem.

The estimated height of Devincenzia (from the ground to the top of the head) is about 2.5 m or more.Large individuals are estimated to have reached a weight of about 350 kg, making them far larger than lions or tigers. The power of the attacks unleashed from their strong legs and beaks was tremendous, and it is thought that Devincenzia preyed on mammals such as giant ground sloths and large rodents.

In the ecosystem of that time, the mighty Devincenzia was one of the apex predators. They may have hunted various types of large animals by running at high speeds, and at times, they might have forcibly stolen prey from other carnivores. If a tall Devincenzia threatened them in earnest, mammals would likely have been terrified and fled.
Even if they encountered a saber-toothed tiger, Devincenzia's massive size and power would have been enough to compete.Just as an ostrich can kick down a lion, it is thought that a Devincenzia's kick could have repelled a saber-toothed tiger. The appearance of these powerful, large Phorusrhacids echoes the image of the dinosaurs of the Mesozoic era.

Devincenzia possessed terrifying strength. In fact, among the terror birds, which were full of tough fighters, there are predators that stand shoulder-to-shoulder with this species. Let's get closer to the true image of the ultimate predators that strode across the lands of South America.

Kelenken: Swift and Tough! The Ultimate Predator Raging Like a Carnivorous Dinosaur

A super-hunter that runs across the earth at a furious speed of over 50 km/h and brings down large prey with its deadly beak and claws. The species that strongly embodies that image is the large terror bird Kelenken guillermoi, which lived in ancient Argentina. Fossils of this species were found in strata from about 15 million years ago and were discovered by a local high school student.
Kelenken's skull reaches 71.6 cm in length, making it the owner of one of the largest beaks among birds. Its estimated height is about 3 m, and it was undoubtedly a predator standing at the top of the ecosystem at the time.

Kelenken's skull was sturdy and powerful, and it is thought that it could have defeated large animals with stabbing attacks from its beak. Furthermore, based on the structure of its legs, it is believed that Kelenken could run at quite high speeds, making it possible to track down and finish off fast prey. Combining speed and attack power, Kelenken is truly the champion of the South American continent.
Although carnivorous mammals such as Borhyaenids also existed on the South American continent at the time, Kelenken was much larger and had the advantage in terms of physique. In the struggle for survival, it is thought that few species could compete with large Phorusrhacids. Kelenken's strength and majesty overwhelmed the mammals.

Inheriting the strength of their carnivorous dinosaur ancestors, these super-powerful Phorusrhacids raged across the land. They continued to fight against numerous mammals and reptiles, successfully continuing to thrive. The souls of the dinosaurs shone brightly even in the Cenozoic era.

And, from among the herbivorous birds, incredibly large species were also born.Among them are giant birds that became the model for the 'mythical Roc'. Next time, I would like to discuss the largest and heaviest herbivorous terrestrial birds in the history of birds!

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Abiko City Museum of Birds explanatory caption
Tobu Zoo explanatory caption
Special Exhibition 'Yokohama Dinosaur Exhibition 2026: A Pictorial Book of Dinosaur Dining' explanatory caption