Phorusrhacidae

Phorusrhacids, often called terror birds, were large birds that could not fly and ate meat. They lived in South America during a time called the Cenozoic era, from about 43 million to just over 25,000 years ago. These birds stood between 1 to 3 meters tall, and some of the biggest could weigh as much as 350 kilograms.

Their closest living relatives today are much smaller birds called seriemas. One big species, Titanis walleri, lived in Texas and Florida in North America, showing that some of these birds moved north from South America long ago. Scientists used to think they lived until humans arrived in North America, but newer studies show they were gone by about 1.8 million years ago.

Some scientists think phorusrhacids might have lived in Africa and Europe too, based on a few old fossils, but these are not very clear. These large birds were top hunters in their environments, and they were part of a fascinating group of animals that lived long before humans.

Description

Phorusrhacids, often called terror birds, were large birds that ate meat and could not fly. They lived in South America millions of years ago. These birds had flexible necks, which helped them swing their heavy heads to catch their prey.

One of the largest terror birds, Kelenken guillermoi, lived about 15 million years ago. Its skull was almost 70 centimetres long with a curved, hooked beak. Most terror birds were smaller, about 60 to 90 centimetres tall, but this one could stand up to 3 metres tall. Scientists think these birds could run very fast. Their feet had four toes with a special curved claw that helped them catch their prey. Recent fossil discoveries show that their skulls were more rectangular than previously believed, with a hooked beak.

Palaeobiology

Phorusrhacids had large hooked beaks and big skulls. Their beaks were very strong and could peck hard, which might have helped them hunt. Some scientists first thought they could only catch small animals, but newer studies show that bigger ones could hunt larger animals too. Smaller phorusrhacids probably focused on smaller prey.

All phorusrhacids likely ate meat. Their beaks curved downward, which is common in meat-eating birds today. Studies of their skulls show they could apply strong downward pressure but not shake their prey side to side.

Diet

Researchers have wondered if phorusrhacids swallowed their prey whole and later spit out undigested bits, like some owls do. One scientist mentioned finding piles of crushed animal bones that looked like owl pellets, but these specimens were never fully described, so it's still unclear.

Classification

The name Phorusrhacidae comes from the type genus Phorusrhacos. When scientists first described it in 1887, they were not sure what the name meant. Today, we think it comes from Greek words for “bearer” and “wrinkles” or “scars.”

After the extinction of the non-bird dinosaurs, mammals started to change and grow, and some birds also grew very big. This included groups like the Gastornithidae, Dromornithidae, Palaeognathae, and the Phorusrhacidae. Phorusrhacids are an extinct group within Cariamiformes, which today only has two species of seriemas. Even though there are many phorusrhacids, scientists do not fully understand how they are related because many fossils are incomplete.

There are 5 subfamilies with 13 genera and 22 species. These birds evolved to live in different ways in their homes.

A study in 2024 found that one group, Bathornis, was closer to seriemas than to phorusrhacids.

Family Phorusrhacidae

• Incertae sedis
  • Genus ?Lavocatavis – Middle Eocene Glib Zegdou Formation of Algeria
  • Genus ?Patagorhacos – Early Miocene Chichinales Formation of Rio Negro Province, Argentina.
  • Genus ?Paleopsilopterus – Lower Eocene (Itaboraian) Itaboraí Formation of Itaboraí, Brazil
  • Genus ?Brontornis – Early to Middle Miocene (Santacrucian–Laventan) Santa Cruz and Monte León Formations, Argentina
  • Genus ?Eleutherornis – Middle Eocene (Bartonian) of Rhône, France and Baselland, Switzerland
• Subfamily Physornithinae
  • Genus Paraphysornis
  • Genus Physornis
• Subfamily Phorusrhacinae
  • Genus Devincenzia
  • Genus Kelenken
  • Genus Phorusrhacos
  • Genus Titanis
• Subfamily Patagornithinae
  • Genus Patagornis
  • Genus Andrewsornis
  • Genus Andalgalornis
• Subfamily Psilopterinae
  • Genus Eschatornis
  • Genus Psilopterus
  • Genus Procariama
• Subfamily Mesembriornithinae
  • Genus Mesembriornis
  • Genus Llallawavis

Alvarenga and Höfling did not include the Ameghinornithidae from Europe in the phorusrhacoids. Scientists think Cariamiformes might be a separate group of birds, Australaves. Their closest living relatives may be Falconidae, Psittaciformes and Passeriformes.

Extinction

During the Miocene and early Pliocene, these large birds increased in South America, showing they were successful hunters.

As land connected North and South America about 2.7 million years ago, new hunters like dogs, bears, and cats arrived from the north. Some scientists thought this caused these birds to disappear. But newer studies show that these birds died out before many of these new hunters arrived. Changes in the environment likely played a bigger role in their disappearance. Some smaller types of these birds may have lived until around 25,000 years ago, but most were gone long before humans arrived in South America.