Colombian rancher finds largest known fossil of three-meters tall “Terror Bird” in Tatacoa Desert

A Colombian rancher has discovered a fossilized bone that points to the existence of a giant terror bird species. The fossil, an enormous leg bone found in the Tatacoa Desert, suggests that this bird stood over three meters tall, making it the largest known member of its kind to date.

The leg bone, identified as the end of a left tibiotarsus—a bone in the lower leg of birds equivalent to a human shinbone—was found nearly 20 years ago by 44-year-old cattle rancher César Augusto Perdomo, who has collected fossils all his life. However, it was not recognized as belonging to a terror bird until recently. In 2023, researchers created a three-dimensional virtual model of the specimen using a portable scanner from Johns Hopkins Medicine, allowing for more thorough analysis.

The research team, composed of scientists from Argentina, Colombia, Peru, and the United States, analyzed the specimen to seek new information about animal life in northern South America millions of years ago. The study was led by terror bird specialist Dr. Federico J. Degrange, a paleontologist from the Argentine scientific organization CONICET. Dr. Degrange is the lead author of a new paper describing the fossil, published in the journal *Papers in Paleontology*, along with co-authors including Dr. Siobhán Cooke, an associate professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine, and Dr. Andrés Link of the Universidad de Los Andes.

The fossil presents probable tooth marks from an extinct caiman, *Purussaurus*, a species believed to have been up to 30 feet long, suggesting how this predator likely met its end. Dr. Cooke said, "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 added, "It was a super predator."

The discovery is significant because it is the northernmost Phorusrhacid found in South America to date, suggesting that these birds may have inhabited more tropical ecosystems. Most terror bird fossils have been identified in southern South America, including Argentina and Uruguay. This finding offers a new perspective on the La Venta ecosystem in the Tatacoa Desert, which houses rich fossil deposits from about 12 million years ago during the Miocene epoch. The region was once a lush and tropical environment with meandering rivers, contrasting with previous indications of a tropical forest ecosystem in La Venta.

Terror birds, or Phorusrhacids, were giant, flightless birds with powerful legs and flesh-ripping beaks, suggesting they were efficient predators. Some hunted by ambushing their prey, while others outran them or chased them until they tired. Dr. Cooke describes, "Terror birds lived on the ground, had limbs adapted for running, and mostly ate other animals."

Bone fragments revealed that this specimen was around 30% larger than other birds of its kind. The recently discovered Phorusrhacid stood at over three meters tall, significantly larger than its relatives, which have been estimated to range from one to three meters in height. This enormous size "also speaks to the trophic levels present in La Venta, and the selective pressures that would allow for ever greater body size," said Dr. Cooke.

The leg bone was analyzed using 3D scanning, highlighting unique features of Phorusrhacid legs. The fossil, believed to be the first of its kind at the site, indicates that the species would have been relatively uncommon among the animals there 12 million years ago. Dr. Cooke said, "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."

The Tatacoa Desert region has been home to terror birds due to their terrifying size and carnivorous tendencies. This discovery indicates that terror birds may have inhabited more tropical ecosystems, contrasting with the open grasslands previously associated with them. Dr. Degrange said, "This suggests it was a mix of open areas, shrubs, and forests, something very similar to what occurred in southern Argentina during the middle Miocene."

The finding also sheds light on the interactions between species in ancient ecosystems. The probable tooth marks from *Purussaurus* suggest a predator-prey relationship. *Purussaurus* was a species of extinct caiman thought to have been up to nine meters (30 feet) long. Dr. Cooke said, "We suspect that the terror bird would have died as a result of its injuries given the size of crocodilians 12 million years ago."

The research offers insights into how giant, flightless birds like terror birds evolved and spread across America. The scarcity of Phorusrhacid fossils in this region may suggest these species were apex predators. Apex predators tend to live in much lower densities than their prey. Dr. Cooke stated, "This is a different type of ecosystem than what we see today or in other parts of the world during a period before South America and North America were connected."

Before this discovery, most La Venta remains indicated it was a tropical forest environment. The presence of a terror bird of this size suggests a more varied ecosystem. The Tatacoa Desert's rich fossil deposits offer a rare snapshot of life in South America before the animals of this previously isolated world encountered those of North America.

The collaboration between scientists and local fossil collectors like César Perdomo highlights the importance of local knowledge in paleontological discoveries. Mr. Perdomo's lifelong passion for collecting fossils, often keeping them under his bed, has contributed significantly to understanding ancient ecosystems. Professional paleontologists relied on his memory to guide their searches. Dr. Cooke, who has worked in the field with Mr. Perdomo and Dr. Link, said, "If César says he saw a beak, he saw it."

The discovery of this giant terror bird fossil not only expands our knowledge of prehistoric predators but also underscores the value of collaboration between local communities and scientific researchers in uncovering the secrets of our planet's ancient past.

Sources: The New York Times, Science Alert, The Scottish Sun, The Sun, u00daltima Hora, Tech, Phys.org

This article was written in collaboration with generative AI company Alchemiq