2013-03-20 22:22:27
About three million years ago, volcanism caused the Isthmus of Panama to emerge, and the continents of North and South America were united. But before that, South America had been isolated for about 150 million years, since it broke away from Africa in the early Cretaceous period. During all that time, the fauna of South America was very particular; especially when it comes to mammals. South American mammals belonged mainly to marsupials, xenarthrans, such as sloths, armadillos, and anteaters, and various groups of ungulates that have disappeared today. The largest predator among mammals was the saber-toothed marsupial, Thylacosmilus, although with its short legs and plantigrade feet it was not a fast runner. This is how land crocodiles like Sebecus, which we have already discussed here, could thrive.
But the top of the ecological pyramid was occupied by animals that had evolved into a form reminiscent of the tyrannosaurs and other large meat-eating dinosaurs of the earlier era. They were large, corpulent, bipedal animals, with strong, narrow, curved and sharp claws on the legs. Although instead of large jaws with sharp teeth they have a very robust hooked beak, instead of a muscular tail they probably have a feathered tail, and instead of arms they have wings, but very short, atrophied wings that are useless for flight. flight. They are the phorusracids, known as terror birds, large carnivorous birds unable to fly. They are between one and three meters tall, can weigh more than 350 kilos, and almost all of them are fast runners; some species reach 70 km/h. But three million years ago, with the arrival of modern carnivores from North America, its decline began. And the last phorusracids disappeared about two million years ago. Phorusrhacids are reminiscent of ostriches, although they are larger and have a much larger head and beak.
Today the phorusrhacids have disappeared, but some close relatives still survive in South America: the chuñas. Chuñas are ratites of the tropical shrubby plains, savannahs, and pampas of Brazil, Bolivia, Paraguay, Uruguay, and Argentina. They are diurnal and stealthy, feeding on the ground but spending the night in trees. They measure just under a meter; they have long necks, legs, and tails, and short wings, and usually stand upright, though they run with their heads down when fleeing. They rarely fly. They have a short bill, and an erectile tuft of feathers adorns their head. They are omnivorous: they feed on frogs, lizards, snakes, snails, insects, chicks, rodents, leaves, seeds and fruits, and in some places they are trained from a young age to guard the chicken coops, as they warn with a loud and sharp cry of the arrival of predators.
The chuñas are, after the ñandúes, the largest endemic land birds of South America. They have sharp claws; the nail of the second finger, very curved, is extensible, similar to that of velociraptors. Although it is not anywhere near as big as those of those carnivorous dinosaurs. Chuñas use this overdeveloped nail to climb trees and tear their prey to pieces, while holding it in their beaks, when they are too large to swallow whole.
The first phorusracids were very similar to schuñas, although more stout and incapable of flight. They appeared about 62 million years ago. They were small and graceful birds, less than a meter tall, and between five and seven kilos in weight. Like the chuñas, they had the second claw of the legs curved and extensible. Since they could not climb trees, their main use must have been hunting.
Over time, the phorusracids became larger. Andalgalornis, which lived between 10 and 5 million years ago, reached 1.5 meters in height, and had, proportionally, the largest beak of any phorusrhacid. With its muscular neck, it was capable of pecking its prey to death.
Mesembriornis, which lived between 10 and 2 million years ago, was one of the last phorusrhacids. It is 1.5 meters tall and its legs are exceptionally muscular. According to some paleontologists, it could reach 90 kilometers per hour, and its way of life was similar to that of the cheetah, hunting small prey on the run. But others believe that its speed could not be that high, and that its powerful leg muscles were used to kick the bones of its prey and to defend its catches from attacks by other predators.
But the most striking phorusrhacids are the giant species, which reach up to three meters in height. There are two groups of giant phorusracins: the brontornithines and the phorusracins. The first, oldest, have very robust legs, and are slow animals. The latter survived until the extinction of the group, and are more agile, with more slender legs.
Among the brontornithines, the best known, and the largest, is Brontornis, the dominant predator in Patagonia during the Miocene period, between 20 and 5 million years ago. Brontornis reaches 2.80 meters in height, and weighs between 350 and 400 kilos. It is not a fast runner, hunts by ambush, and is also an opportunistic scavenger; Thanks to its enormous size, it can steal prey from smaller predators. Although some recent studies of the anatomy of Brontornis suggest that it was not a phorusracid, but rather a giant duck; a giant carnivorous duck, mind you. But not all paleontologists agree with this classification.
Paraphysornis is another brontornithine, somewhat smaller, that lived in southeastern Brazil 23 million years ago. There is no doubt about this species, it is really a phorusracid. It stands two meters tall, with a skull two feet long.
Among the phorusracinos, the giant agile phorusracins, is Phorusrhacos, the first discovered species of this group and the one that gave it its name. Its discoverer was the Argentine naturalist Florentino Ameghino, who in 1887 described a piece of mandible that he identified as belonging to a xenarthro mammal. The name, which means “wrinkle bearer,” refers to the rough surface of the jaw bone. A few years later, in 1891, it was recognized that it was a bird. Phorusrhacos, 2.5 meters tall and 130 kilos in weight, inhabited forests and grasslands in Patagonia between 20 and 10 million years ago. The skull of Phorusrhacos measures two feet in length, of which half correspond to the beak, robust and hooked. The wings, though stunted, are not useless; They function as short arms ending in hook-like claws, with which Phorusrhacos can strike down its prey. What we don’t know for sure is how he killed them. It would either catch them in its beak and slam them repeatedly against the ground, as schuñas do today, or it would pierce its victim’s skull with a peck, killing it instantly.
The largest phorusracid, and the largest known predatory bird, was discovered in Patagonia in 2006 and described in 2007. It is Kelenken, named after a fearsome spirit from Tehuelche mythology that takes the form of a gigantic bird of prey. . Kelenken’s fossil remains, a skull and fragments of a foot and a paw, were discovered at the Comallo railway station, near the city of Bariloche, by Guillermo Oscar Aguirrezabala, and are housed in the Bariloche Paleontological Museum.
Kelenken lived about 15 million years ago, stands over three meters tall and weighs over 160 kilos. The skull exceeds 70 centimeters in length, of which almost 46 correspond to the beak, narrow and hooked like that of an eagle. Despite his size, he is a fast runner; adults reach 50 km/h, and hatchlings can reach 80 km/h. Their way of life must have been similar to that of Phorusrhacos.
The phorusracids were not restricted to South America. A fragment of phorusracid bone has been found in Antarctica, the origin of which is easy to explain, since South America and Antarctica did not fully separate until about fifty million years ago. On the other hand, one of the last phorusracids, Titanis, lived in North America; its fossil remains have been found in Texas and Florida. We have already said that the arrival of modern carnivorous mammals from North America was the death sentence for phorusracids. But its extinction was not sudden. After the appearance of the Isthmus of Panama, some phorusracids managed to invade North America, and survived there for a while. This is the case of Titans.
Titanis was 2.5 meters tall and weighed about 150 kilos, although it is likely that there were large differences between males and females. She reached 65 kilometers per hour top speed. It was very similar to its South American relatives, such as Phorusrhacos, although somewhat more robust. But in the end the carnivorous mammals won out, and Titanis went extinct about two million years ago, before any humans reached the Americas. Unfortunately, no one has ever seen a live phorusracid.
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