This fragment of a terror bird’s left tibiotarsus, a lower leg bone in birds equivalent to that of a human tibia or shin bone, dates to around 12 million years ago during the Miocene epoch.
Degrange et al.
Nearly 20 years ago, while repairing a fence on his ranch in Colombia, fossil collector César Perdomo found the middle leg bone of a bird. The 12-million-year-old fossil, known as a tibiotarsus, belonged to a now-extinct creature in the Phorusrhacidae family, which was made up of mostly flightless, giant, meat-eating birds known collectively as “terror birds.”
These top predators could be either the size of a dog or grow up to nine feet tall. Now, in a new study published this week in Papers in Paleontology, researchers suggest this fossil belonged to a previously unknown species that could’ve grown from 5 to 20 percent bigger than other terror birds.
“We are talking about a species that was larger than 2.5 meters [8.2 feet] and weighed more than 150 kilograms [330 pounds],” lead author Federico Degrange, a paleontologist at Argentina’s science agency CONICET, tells Newsweek’s Aristos Georgiou.
Perdomo’s discovered fragment of a tibiotarsus is the northernmost record for terror birds in South America, the authors write in the study, suggesting these animals might have also lived in more tropical environments. Previously, fossils from terror birds had mostly been found in Argentina near the southernmost part of the continent, or in more northern regions like Texas and Florida, leaving a big gap in between.
A drawing of Paraphysornis brasiliensis, a terror bird from the Early Miocene of Brazil. The new species recently discovered in Colombia is thought to be larger than any other known terror bird.
Derivative work: Snowmanradio (talk), Original image: Nobu Tamura, via Wikimedia Commons under CC BY 3.0
For Siobhan Cooke, a paleontologist at Johns Hopkins University and co-author of the study, the fossil confirms that terror birds were part of the landscape in what is now Colombia, not merely something “transient,” she tells the New York Times’ Jennie Erin Smith. The finding shows that the other terror birds found in Texas and Florida “weren’t birds from Patagonia that decided to walk north 5,000 miles.”
The region where the bone was found is known as La Venta, a fossil bed that’s part of the Tatacoa Desert in Colombia. It was previously thought that La Venta was a tropical ecosystem, but the study suggests it might have been a mixture of shrubs and forests during the Miocene, since terror birds preferred open land to hunt.
“A giant bird that ate meat on the landscape—that’s fundamentally cool,” Cooke tells Discover magazine’s Paul Smaglik. “And it’s so outside of what we are aware of today.”
The Tatacoa Desert, located north of the Colombian department of Huila, has been the source of many fossil discoveries.
Jorge Láscar via Flickr under CC BY 2.0
Thomas LaBarge, a researcher at Indiana University Bloomington who was not involved with this paper, studies the reasons behind the terror birds’ evolution. Why were terror birds so large? Previously, scientists thought the expansion of open grasslands and the absence of predators might have enabled the giant birds to grow, but LaBarge found it was also related to competition with other birds, reports the New York Times.
Two terror bird species of similar size with the same hunting style “could not coexist for more than a couple million years. One or the other would become extinct,” he tells the outlet.
Interestingly, a pair of indentations on the recently described bone suggested the bird might have met its fate in the jaws of a giant relative of the crocodile. The prehistoric bite marks are thought to have been made by a Purussaurus, an extinct caiman from the Miocene that grew more than 40 feet long.
“We suspect that the terror bird would have died as a result of its injuries given the size of crocodilians 12 million years ago,” Cooke says in a statement.
