Fossil of huge terror bird offers new information about wildlife in South America 12 million years ago

The evidence lies in the leg bone of the terror bird described in new paper published Nov. 4 in Palaeontology. The study was led by Federico J. Degrange, a terror bird specialist, and included Siobhán Cooke, Ph.D., associate professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine. The bone, found in the fossil-rich Tatacoa Desert in Colombia, which sits at the northern tip of South America, is believed to be the northernmost evidence of the bird in South America thus far.

The size of the bone also indicates that this terror bird may be the largest known member of the species identified to date, approximately 5%-20% larger than known Phorusrhacids, Cooke says. Previously discovered fossils indicate that terror bird species ranged in size from 3 feet to 9 feet tall.

"Terror birds lived on the ground, had limbs adapted for running, and mostly ate other animals," Cooke says.

The bird's leg bone was found by Cesar Augusto Perdomo, curator of the Museo La Tormenta, nearly 20 years ago, but was not recognized as a terror bird until 2023. In January 2024, researchers created a three-dimensional virtual model of the specimen using a portable scanner from Johns Hopkins Medicine, allowing them to analyze it further.

The fossil, the end of a left tibiotarsus, a lower leg bone in birds equivalent to that of a human tibia or shin bone, dates back to the Miocene epoch around 12 million years ago. The bone, with deep pits unique to the legs of all Phorusrhacids, is also marked with probable teeth marks of an extinct caiman -- Purussaurus -- a species that is thought to have been up to 30 feet long, Cooke says.

"We suspect that the terror bird would have died as a result of its injuries given the size of crocodilians 12 million years ago," she says.

Most terror bird fossils have been identified in the southern part of South America, including Argentina and Uruguay.

The Phorusrhacid fossil discovery as far north as Colombia suggests that it was an important part of predatory wildlife in the region. Importantly, this fossil helps the researchers better understand the animals living in the region 12 million years ago. Now a desert, scientists believe this region was once an environment full of meandering rivers. This giant bird lived among primates, hoofed mammals, giant ground sloths and armadillo relatives, glyptodonts, that were the size of cars. Today, the seriema, a long-legged bird native to South America that stands up to 3-feet-tall, is thought to be a modern relative of Phorusrhacid.

"It's a different kind of ecosystem than we see today or in other parts of the world during a period before South and North America were connected," Cooke says

Believed to be the first of its kind from the site, the fossil indicates that the species would have been relatively uncommon among the animals there 12 million years ago, Cooke says.

"It's possible there are fossils in existing collections that haven't been recognized yet as terror birds because the bones are less diagnostic than the lower leg bone we found," she says.

For Cooke, the finding helps her imagine an environment one can no longer find in nature.

"It would have been a fascinating place to walk around and see all of these now extinct animals," she says.

In addition to Cooke and Perdomo, the study's authors include first author Federico Javier Degrange of Centro de Investigaciones en Ciencias de la Tierra; Luis G. Ortiz-Pabon of Universidad de Los Andes, Carrera, Bogotá, Colombia and Universidad Nacional de Colombia, Carrera, Bogotá; Jonathan Pelegrin of Universidad del Valle, Colombia, and Universidad Santiago de Cali, Colombia; Rodolfo Salas-Gismondi of Universidad Nacional Mayor de San Marcos, Avenida Arenales, Perú; and Andrés Link of Universidad de Los Andes, Carrera Bogotá, Colombia.