Temporal range: Late Cretaceous, 97–94Ma
|Restored skeleton, Naturmuseum Senckenberg|
Bonaparte & Coria, 1993
|Species:||† A. huinculensis|
Bonaparte & Coria, 1993
Argentinosaurus (AR-jen-TEE-noh-SAW-rus meaning "Argentinian lizard") is a genus of titanosaur sauropod dinosaur first discovered by Guillermo Heredia in Argentina. The generic name refers to the country in which it was discovered. The dinosaur lived on the then-island continent of South America somewhere between 97 and 94 million years ago, during the Late Cretaceous Epoch. It is among the largest known dinosaurs.
The first fossils identified as Argentinosaurus were found in 1987 by a rancher in Argentina, who mistook the leg for a giant piece of petrified wood. A gigantic backbone was also found, and was almost as high as a man.
The type species of Argentinosaurus, A. huinculensis, was described and published in 1993 by the Argentinian palaeontologists José F. Bonaparte and Rodolfo Coria. Its more specific time-frame within the Cretaceous is the late Cenomanian faunal stage, ~96 to 94 million years ago. The fossil discovery site is in the Huincul Formation of the Río Limay Subgroup in Neuquén Province, Argentina (the Huincul Formation was a member of the Río Limay Formation according to the naming of the time).
Not much of Argentinosaurus has been recovered. The holotype included only a series of vertebrae (six from the back, five partial vertebrae from the hip region), ribs of the right side of the hip region, a part of a rib from the flank, and the right tibia (lower leg bone). One of these vertebra had a length of 1.59 meters (spine to the ventral border) and the tibia was about 155 centimeters (58 inches). In addition to these bones, an incomplete femur (upper leg bone, specimen number MLP-DP 46-VIII-21-3) is assigned to Argentinosaurus; this incomplete femur shaft has a minimum circumference of about 1.18 meters. The proportions of these bones and comparisons with other sauropod relatives allow paleontologists to estimate the size of the animal.
An early reconstruction by Gregory S. Paul estimated Argentinosaurus at between 30–35 metres (98–115 ft) in length and with a weight of up to 80–100 tonnes (88–110 short tons). The length was also found by Benson et al. (2012). In 2007, a similar length of 35 metres (115 ft) was found by Tim Haines and Paul Chambers, but a larger weight of 90 tonnes (89 long tons; 99 short tons) was also found. The length of the skeletal restoration mounted in Museo Carmen Funes is 39.7 metres (130 ft) long and 7.3 metres (24 ft) high. This is the longest reconstruction in a museum and contains the original material, including a mostly complete fibula. Other estimates have compared the fragmentary material to relatively complete titanosaurs to help estimate the size of Argentinosaurus. In 2006 Carpenter used the more complete Saltasaurus as a guide and estimated Argentinosaurus at 30 metres (98 ft) in length. An unpublished estimate used published reconstructions of Saltasaurus, Opisthocoelicaudia, and Rapetosaurus as guides and gave shorter length estimates of between 22–26 metres (72–85 ft). Weight estimates are less common, but Mazzetta et al. (2004) provide a range of 60–88 tonnes (66–97 short tons), and consider 73 tonnes (80 short tons) to be the most likely, making it the heaviest sauropod known from good material.
In 2013, in a study published in Plos One on October 30, 2013 by Dr. Bill Sellers, Rudolfo Coria, Lee Margetts et al, Argentinosaurus was digitally reconstructed to test its locomotion for the first time. The results of the biomechanics study revealed that Argentinosaurus was mechanically competent at a top speed of 2m/s (5 mph) given the great weight of the animal and the strain that its joints were capable of bearing. The results further revealed that much larger terrestrial vertebrates might be possible, but would require significant body remodeling and possible sufficient behavioral change to prevent joint collapse.
Argentinosaurus was, like all sauropods, a herbivore. It probably used its long neck to reach into conifers, or sweep the ground in search of ferns and bushes. Once swallowed, the food would have needed to travel all the way down the neck before entering the stomach. Inside the stomach, the vegetation would have been ground or broken down by smooth stones known as gastroliths.
Argentinosaurus adults were some of the largest animals ever, but their hatchlings were not. One article found that Argentinosaurus hatchlings would have had to grow 25 000 times their original size to be able to reach their maximum size. Argentinosaurus probably traveled in herds of 15 to 20 animals, including juveniles. Young animals were vulnerable to attacks from predators, and avoid getting stuck. It is thought that only a handful of juveniles would be lucky enough to make it into adulthood. Animals related to Argentinosaurus have been preserved from fossilized eggs. The eggs indicate every year, hundreds of adults would gather just to nest. Wide, flat floodplains have been identified as the preferred nesting sites. The eggs were around 22 centimetres (8.7 in) in diameter, and each adult probably layed 3 to 13 eggs a season. Once hatched, it took about 15 years for the tiny hatchlings to reach adulthood, and a gigantic size.
Argentinosaurus is featured prominently in the permanent exhibition Giants of the Mesozoic at Fernbank Museum of Natural History in Atlanta, Georgia, USA. This display depicts a hypothetical encounter between Argentinosaurus and the carnivorous theropod dinosaur Giganotosaurus. Contemporary fossils of Cretaceous Period plants and animals are included in the exhibition, including two species of pterosaurs, providing a snapshot of a prehistoric ecosystem in what is now the modern Patagonia region of Argentina. At 35 m (117 ft) long, this skeletal reconstruction represents one of the largest dinosaur mounts ever to be assembled.
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