2013-11-09 14:50:16
95 million years ago, in the early Late Cretaceous, South America was a large island with a unique dinosaur fauna that evolved independently of the rest of the world. While in the northern hemisphere sauropods, the enormous long-necked quadrupedal dinosaurs, were in decline, replaced by horned ceratopsians and bipedal ornithopods as the dominant herbivores, in South America and other southern hemisphere continents sauropods maintained their hegemony with the Titanosaur group, which includes some of the largest land animals that have ever lived.
Titanosaurs are characterized by their small, broad, and elongated heads, compared to those of other sauropods. The nostrils are large, and the teeth are small. The tail is long and thin, like a whip, though not as long as Diplodocus and its relatives. Its skin is decorated with a mosaic of small rounded bony plates around larger ones.
Although titanosaur vertebrae are solid, and not hollow like other sauropods, their backbones are more flexible, and they are probably more agile than their relatives. They have narrow hips, but very broad shoulders, so that in their tracks the paw prints on one side are wide apart from those on the other.
Titanosaurs nest in groups. Two fossilized titanosaur nesting areas are known, one in Argentine Patagonia and the other in Catalonia, northeastern Spain. Hundreds of females gather to lay eggs. With their hind legs they dig shallow holes where they lay their eggs, which they cover with earth and vegetation. The nests are so close together that there is not room for all the mothers to attend to them; once the laying is finished, the eggs remain abandoned until hatching.
The heaviest titanosaur, and the largest land animal of all time, could have been Argentinosaurus, the Argentine lizard. The argentinosaurus lived in the province of Neuquén, in western Argentina, at the foot of the Andes, about 95 million years ago. Back then, Neuquén was an arid region, with seasonal water currents. Few fossils from the time have been found in the region, but we do know of some dinosaurs contemporaneous with the argentinosaurus, such as the smaller sauropod Cathartesaura, and various carnivores. Two of these, Skorpiovenator, six meters long and weighing two tons, and Ilokelesia, were abelisaurids, a group of carnivorous dinosaurs from the southern hemisphere characterized by their atrophied arms and the ridges and grooves that adorn their skulls. But the dominant predator in the region, and the only one that could disturb the argentinosaurus, was Mapusaurus, which belongs to the group of carcharodontosaurs, the shark-toothed lizards, a group of large carnivores from the southern hemisphere that includes some of the largest predators. largest terrestrial that have existed; even bigger, but also more slender, than the famous Tyrannosaurus.
The mapusaur is a predator that lives in family groups, in which young individuals of five and a half meters in length coexist with adults that reach five meters in height and thirteen in length and weigh about five tons. The mapusaur’s head is relatively small, and the arms are short, with three fingers on each hand; although they are not atrophied like those of the abelisaurids. Hunting in groups, mapusaurs could prey even on huge argentinosaurus, although, as is always the case among predators, they most likely selected the weakest prey on their hunts: hatchlings or old or sick individuals.
An adult argentinosaurus would have been a fearsome opponent even for a herd of mapusaurs. It came to measure more than thirty meters long, and its weight is estimated at about eighty tons. He could raise his head more than twenty meters high.
The most recent studies, published this past October by Rodolfo Coria, from the National University of Río Negro and the Carmen Funes Museum in Plaza Huincul, in Argentina, and William Sellers, Lee Margetts and Phillip Manning, from the University of Manchester, have reconstructed the mode of locomotion of the argentinosaurus. According to their results, the titanosaur moved with a amble gait, moving both legs on the same side at the same time, at a maximum speed of two meters per second, or about seven kilometers per hour.
The remains of Argentinosaurus were discovered in 1989 by Guillermo Heredia, a farmer at the “Las Overas” ranch, near the town of Plaza Huincul, in the province of Neuquén, in western Argentina. In Argentina, as in other countries of the southern cone, the haciendas, or estancias, are divided into posts for their exploitation; the puestero is the person who is in charge of one of those positions. Guillermo Heredia, 90 years old, informed the municipal museum, the aforementioned Carmen Funes Museum, of the discovery on his land of what appeared to be fossils. A preliminary excavation brought to light a tibia, but it took summer to unearth the rest of the fossil bones: a few vertebrae and ribs, part of the sacrum, and a fragment of a femur. The remains are scarce, but its size gives an idea of the size of the animal: one of the vertebrae measures one meter sixty in length, and the tibia one fifty-five; the femur has a minimum perimeter of one meter eighteen. Although the remains are highly incomplete, several museums have made reconstructions of the animal’s skeleton, based on related species. They can be seen, in addition to the Carmen Funes Museum in Plaza Huincul, at the Fernbank Museum of Natural History in Atlanta, in the United States, and at the Senckenberg Museum of Natural History, in Frankfurt, Germany.
The argentinosaurus is considered to be the heaviest dinosaur known from significant remains, but it would be too bold to claim that it is the largest land animal that ever lived. Given the random nature of the fossilization process, the fossil record is scant and incomplete; We only know a small fraction of all the animal species that have ever existed, and even of these we can rarely be sure of the maximum size they could reach, either because we have very few specimens, often only one, or because only we have fragments from which it is not possible to reliably reconstruct the entire animal. In this situation are several species that could be even larger than the argentinosaurus.
In 1878, American paleontologist Edward Drinker Cope received a five-foot-long fragment of vertebra found in Colorado. With such scant material he published the description of a new species, Amphicoelias fragillimus, a relative of Diplodocus. If Cope’s interpretation is correct, the complete vertebra would have measured 2.7 meters, and the animal would have had a length of between 40 and 60 meters, and a weight of more than 100 tons. But the fossil has been lost, and today we only have Cope’s drawings and notes. At that time, the current means of conservation were not available, and it is very possible that the fossil, described by Cope himself as “very fragile”, disintegrated in the hands of the paleontologist.
A more recent case is that of Bruhathkayosaurus, which according to calculations could have weighed 140 tons. The fossil remains of Bruhathkayosaurus, two hip bones, part of a femur, a two-meter-long tibia, a radius and a caudal vertebra, dating back about 70 million years, were found in southern India. in 1989. Its discoverers initially classified it as a carnosaur, a bipedal predatory dinosaur, but due to the enormous size of the bones, paleontologists were later inclined to classify it as a titanosaur, the group to which the argentinosaurus belongs. The problem is that, as in the previous case, we no longer have the fossils. It seems they were lost in a flood, and all we have left are rough sketches of the bones. Furthermore, the published description left a lot to be desired, and some suspect that the Bruhathkayosaurus fossils were actually petrified wood. For now, the argentinosaurus maintains its title of heaviest dinosaur.
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