Fossils of Giant Carnivorous Birds Found in Argentina
Paleontologists have unearthed the fossilized remains of large teratornithid birds at four localities in central Argentina.
Teratorns are members of Teratornithidae, a highly diversified guild of large carnivorous flying birds that lived between 25 million and 12,000 years ago.
Their fossil record is limited exclusively to North and South America. The first teratorn fossils were discovered in 1909 in famous La Brea Tar Pits in California, the United States.
Teratorns are related to living storks and New World vultures such as turkey vultures and condors.
They are among the largest flying birds that ever existed: with a wingspan of up to 7 m (23 feet) and an estimated mass of 70 kg, the teratorn species Argentavis magnificens from the Late Miocene of Argentina is one of the largest flying birds known, only rivaled by the Eocene and Neogene pelagornithids.
“It is believed that teratorns originated in South America because their oldest remains were found in 25- to 5-million-year-old deposits in Brazil and Argentina,” said Dr. Marcos Cenizo, a paleontologist in the Centro de Ciencias Naturales, Ambientales y Antropológicas at the Fundación de Historia Natural Félix de Azara – Universidad Maimónides.
“After this period, teratorns disappeared from the South American fossil record, but became remarkably abundant and diverse in North America until their extinction at the end of the Pleistocene period, some 12,000 years ago.”
“The absence of these gigantic birds during the last 5 million years in South America was a mystery — until now.”
Dr. Cenizo and colleagues examined four new teratorn specimens from localities of central Argentina that range in age from the Late Middle to the Early Late Pleistocene.
“The first specimen that we identified was found in the 1980s at the site of Playa del Barco,” they said.
“We then found two more fossils: one in Centinela del Mar Natural Reserve, close to Mar del Sud and Miramar; and the other in the Salado de Santa Fe river, near Manucho.”
“One more specimen was added, previously reported as a condor, which was collected between 1930 and 1950.”
The new specimens are comparable in size and morphology to a previously known species called Teratornis merriami.
However, they exhibit a set of divergent characters and probably belong to new species.
“The available evidence suggests that forms related to Teratornis lived in the South American Pampas around the time of the Last Interglacial (MIS 5), but they were restricted to North America during the latest Pleistocene (late MIS 3-early MIS 1),” the researchers said.
“The contrasting latest Pleistocene record of teratorns between North and South America is not easy to understand, especially because the supposed flight capacity of these birds did not prevent them from crossing large geographical barriers.”
“Although a bias in the fossil record cannot be ruled out, it is possible that the teratorns were limited in South America by paleoclimatic-paleoecological factors as yet undetermined, and/or that the northern and southern Pleistocene species had very dissimilar specializations.”
The new specimens also shed more light on the paleobiology of teratorn birds.
“The early assumption that teratorns were vulture-like birds with a strict scavenger or raptorial behavior was based on the presence of a sharply hooked beak, their comparable body size and superficial similarity to the condors in limb proportions and morphology, as well as its frequent associated finding with cathartids and other large carnivorous birds,” the authors said.
“However, the relatively weak legs and claws observed in teratorns are not consistent with raptorlike features, and the distinctive morphology of the pectoral and pelvic girdles, skull and jaws appear to be incompatible with vulture-like ecology.”
“Their functional affinities are closer to an opportunistic-piscivorous bird such as the ciconiiforms and pelecaniforms that swallow whole prey.”
M. Cenizo et al. First Pleistocene South American Teratornithidae (Aves): new insights into the late evolutionary history of teratorns. Journal of Vertebrate Paleontology, published online July 9, 2021; doi: 10.1080/02724634.2021.1927064