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Late Extinction

Uruguayan fossil indicates that the terror bird disappeared shortly before the arrival of humans in the Americas

EDUARDO BRETTASDrawing of the Psilopterus bird, which the new species resembledEDUARDO BRETTAS

The so-called enormous, carnivorous terror birds, incapable of flying, disappeared later than had originally been believed and were almost contemporaries of modern man. Paleontologists from Brazil and Uruguay discovered a Phorusrhacidae fossil, the scientific name of this family of extinct birds, which had lived in the vicinity of what is today Montevideo about 15 thousand years ago, only 2 thousand years before the date most widely accepted as the one on which Homo Sapiens arrived in the Americas. This discovery is the latest vestige of a member of these mythical predators that probably appeared in South America approximately 65 million years ago, shortly after the extinction of the dinosaurs.

Before the Uruguayan fossil was identified – it seems to belong to a new species that has not been described in scientific literature yet – researchers had believed that the terror birds had disappeared from the continent approximately 2 million years ago. Vestiges of the Titanis walleri species – the only Phorusrhacidae that migrated to North America – found in the United States corroborated this hypothesis. “Now we have evidence that the terror birds were extinguished later,” states paleontologist Herculano Alvarenga, founder and director of the Natural History Museum of Taubaté, in the State of São Paulo. Alvarenga is one of the scientists who discovered the fossil. An article with a description of the fossil was published in the May issue of German journal Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen.

A bone fragment of the animal’s right leg was found in the sediments from the end of the Pleistocene period. The sediments comprise the Dolores Formation, located in the municipal region of La Paz, near Uruguay’s capital city. “This region had many fossils of the South American mega fauna,” says Washington Jones, of the Natural History Museum of Montevideo, who co-authored the article. A bone fragment of the tarsometatarsus, the bone that connects the bird’s leg (fibula and tibia) to its fingers led Alvarenga to classify the fragment as belonging to the Phorusrhacidae. “Our eyes are trained to recognize anatomical details that are characteristic of various groups of birds,” says the paleontologist from Taubaté.

Orthopedist and paleontologist
Alvarenga, who is a physician specialized in orthopedics, is passionate about bones and winged beings. Besides his work as an orthopedist, Alvarenga has dedicated his time to the study of bird fossils ever since the late 1970’s. He got a doctorate degree in paleontology from the University of São Paulo in 1990’s and his PhD. thesis focused on terror birds. The high quality of his scientific work and the fact that he heads a museum with a fossil collection of more than one thousand bird species have earned him the respect of the paleontologist community in Brazil and abroad. Among the two species of Phorusrhacidae discovered in Brazil and described by Alvarenga is a complete skeleton of the Paraphysornis brasiliensis, a two-meter high predator that terrorized the Vale do Paraíba region 23 million years ago because of its hooked beak. Alvarenga is a reference for this family of birds; in 2003, he published a scientific review article on 14 genres and 18 known species of these ancient carnivores. He recently wrote a chapter on terror birds that is part of the book Living dinosaurs: the evolutionary history of modern birds, launched early this year in the United States.

GUSTAVO LECUONA, 2009Details of the fossilGUSTAVO LECUONA, 2009

Due to the lack of material near the capital city of Uruguay, it is impossible to reconstitute a full replica of this most recent vestige of a terror bird. The biggest known examples of these predators, such as some fossils of the T. walleri and Brontornis burmeisteri, show that they were up to three meters tall and weighed 180 kilos. The bone fragment retrieved in Uruguay suggests that the possibly new species was one of the smallest examples of the Phorusrhacidae. “There is no doubt that the bone belonged to a relatively small animal,” says Alvarenga. The animal probably weighed no more than 10 kilos and  was no more than one meter tall. It was probably similar to the terror birds of the Psilopterus genre, which, in turn, resembled the very contemporary Seriema bird (Cariama cristata). The seriema bird, which is native to South America, is considered the live species that is most closely related to the Phorusrhacidae.

It is believed that the terror birds became extinct when the huge carnivore mammals, such as the saber-toothed tigers and the ancestors of wolves, migrated from North America to South America. The inbreeding of the fauna from the two main parts of the continents intensified after the creation of the Isthmus of Panama that, three million years ago, facilitated the journeys of bigger animals. For some still unknown reason, the Phorusrhacidae species, which had no teeth, were less competitive when confronted by the predators coming from the North. The same process might have been decisive to the disappearance of other ancient animals in South America, such as the giant sloths. If this actually occurred, the Uruguayan fossil indicates that the extinction of the Phorusrhacidae was relatively slow. “The possibility that the terror birds had contact with humans is not impossible but, very unlikely, even in spite of this new discovery,” says Jones.

Scientific article
ALVARENGA, H. et al. The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. v. 256, n. 2, p. 229-34. May 2010.