Argentinosaurus (meaning "lizard from Argentina") is a genus of giant sauropod dinosaur that lived during the Early Cretaceous period in what is now Argentina. Although it is only known from fragmentary remains, Argentinosaurus was one of the largest known land animals of all time, measuring long and weighing . It was a member of Titanosauria, the dominant group of sauropods during the Cretaceous.
The first Argentinosaurus bone was discovered in 1987 by a farmer on his farm near the city of Plaza Huincul. A scientific excavation of the site led by the Argentine palaeontologist José Bonaparte was conducted in 1989, yielding several back vertebrae and parts of a sacrum—fused vertebrae between the back and tail vertebrae. Additional specimens include a complete femur (thigh bone) and the shaft of another. Argentinosaurus was named by Bonaparte and the Argentine palaeontologist Rodolfo Coria in 1993; the genus contains a single species, A. huinculensis, after its place of discovery, Plaza Huincul.
The fragmentary nature of Argentinosaurus remains makes their interpretation difficult. Arguments revolve around the position of the recovered vertebrae within the vertebral column and the presence of accessory articulations between the vertebrae that would have strengthened the spine. A computer model of the skeleton and muscles estimated this dinosaur had a maximum speed of 7.2 km/h (5 mph) with a pace, a gait where the fore and hind limb of the same side of the body move simultaneously. The fossils of Argentinosaurus were recovered from the Huincul Formation, which was deposited in the Albian stage and contains a diverse dinosaur fauna, including the giant theropod Mapusaurus.
Discovery
The first Argentinosaurus bone, which is now thought to be a fibula (calf bone), was discovered in 1987 by Guillermo Heredia on his farm "Las Overas" about east of Plaza Huincul, in Neuquén Province, Argentina. Heredia, initially believing he had discovered petrified logs, informed the local museum, the Museo Carmen Funes, whose staff members excavated the bone and stored it in the museum's exhibition room. In early 1989, the Argentine palaeontologist José F. Bonaparte initiated a larger excavation of the site involving palaeontologists of the Museo Argentino de Ciencias Naturales, yielding a number of additional elements from the same individual. The individual, which later became the holotype of Argentinosaurus huinculensis, is catalogued under the specimen number MCF-PVPH 1.
Separating fossils from the very hard rock in which the bones were encased required the use of pneumatic hammers. The additional material recovered included seven dorsal vertebrae (vertebrae of the back), the underside of the sacrum (fused vertebrae between the dorsal and tail vertebrae) including the first to fifth and some sacral ribs, and a part of a dorsal rib (rib from the flank). These finds were also incorporated into the collection of the Museo Carmen Funes.
Bonaparte presented the new find in 1989 at a scientific conference in San Juan. The formal description was published in 1993 by Bonaparte and the Argentine palaeontologist Rodolfo Coria, with the naming of a new genus and species, Argentinosaurus huinculensis. The generic name means "Argentine lizard", while the specific name refers to the town Plaza Huincul. Bonaparte and Coria described the limb bone discovered in 1987 as an eroded tibia (shin bone), although the Uruguayan palaeontologist Gerardo Mazzetta and colleagues reidentified this bone as a left fibula in 2004. In 1996, Bonaparte referred (assigned) a complete femur (thigh bone) from the same locality to the genus, which was put on exhibit at the Museo Carmen Funes. This bone was deformed by front-to-back crushing during fossilization. In their 2004 study, Mazzetta and colleagues mentioned an additional femur that is housed in the La Plata Museum under the specimen number MLP-DP 46-VIII-21-3. Though not as strongly deformed as the complete femur, it preserves only the shaft and lacks its upper and lower ends. Both specimens belonged to individuals equivalent in size to the holotype individual. As of 2019, however, it was still uncertain whether any of these femora belonged to Argentinosaurus.
Description Size
Argentinosaurus is among the largest known land animals, although its exact size is difficult to estimate because of the incompleteness of its remains. To counter this problem, palaeontologists can compare the known material with that of smaller related sauropods known from more complete remains. The more complete taxon can then be scaled up to match the dimensions of Argentinosaurus. Mass can be estimated from known relationships between certain bone measurements and body mass, or through determining the volume of models.
A reconstruction of Argentinosaurus created by Gregory Paul in 1994 yielded a length estimate of . Later that year, estimates by Bonaparte and Coria suggesting a hind limb length of , a trunk length (hip to shoulder) of , and an overall body length of were published. In 2006, Kenneth Carpenter reconstructed Argentinosaurus using the more complete Saltasaurus as a guide and estimated a length of . In 2008, Jorge Calvo and colleagues used the proportions of Futalognkosaurus to estimate the length of Argentinosaurus at less than . In 2013, William Sellers and colleagues arrived at a length estimate of and a shoulder height of by measuring the skeletal mount in Museo Carmen Funes. During the same year, Scott Hartman suggested that because Argentinosaurus was then thought to be a basal titanosaur, it would have a shorter tail and narrower chest than Puertasaurus, which he estimated to be about long, indicating Argentinosaurus was slightly smaller. In 2016, Paul estimated the length of Argentinosaurus at , but later estimated a greater length of or longer in 2019, restoring the unknown neck and tail of Argentinosaurus after those of other large South American titanosaurs.
Paul estimated a body mass of for Argentinosaurus in 1994. In 2004, Mazzetta and colleagues provided a range of and considered to be the most likely mass, making it the heaviest sauropod known from good material. In 2013, Sellers and colleagues estimated a mass of by calculating the volume of the aforementioned Museo Carmen Funes skeleton. In 2014 and 2018, Roger Benson and colleagues estimated the mass of Argentinosaurus at , but these estimates were questioned due to a very large error range and lack of precision. In 2016, using equations that estimate body mass based on the circumference of the humerus and femur of quadrupedal animals, Bernardo Gonzáles Riga and colleagues estimated a mass of based on an isolated femur; it is uncertain whether this femur actually belongs to Argentinosaurus. In the same year, Paul moderated his earlier estimate from 1994 and listed the body mass of Argentinosaurus at more than . In 2019, Paul moderated his 2016 estimate and gave a mass estimate of based on his skeletal reconstructions (diagrams illustrating the bones and shape of an animal) of Argentinosaurus in dorsal and lateral view. In 2020, Campione and Evans also yielded a body mass estimate of approximately . In 2023, Paul and Larramendi proposed that the holotype would have weighed between at maximum. They further suggested that the enigmatic, fragmentary Bruhathkayosaurus possibly weighed more, between .
While Argentinosaurus was definitely a massive animal, there is disagreement over whether it was the largest known titanosaur. Puertasaurus, Futalognkosaurus, Dreadnoughtus, Paralititan, "Antarctosaurus" giganteus, and Alamosaurus have all been considered to be comparable in size with Argentinosaurus by some studies, although others have found them to be notably smaller. In 2017, Carballido and colleagues considered Argentinosaurus to be smaller than Patagotitan, since the latter had a greater area enclosed by the , , and of its anterior dorsal vertebrae. However, Paul found Patagotitan to be smaller than Argentinosaurus in 2019, due to the latter's dorsal column being considerably longer. Even if Argentinosaurus was the largest-known titanosaur, other sauropods including Maraapunisaurus and a giant mamenchisaurid, may have been larger, although these are only known from very scant remains. Some diplodocids, such as Supersaurus and Diplodocus may have exceeded Argentinosaurus in length despite being considerably less massive. The mass of the blue whale, however, which can be greater than , still exceeds that of all known sauropods.
Vertebrae
Argentinosaurus likely possessed 10 dorsal vertebrae, like other titanosaurs. The vertebrae were enormous even for sauropods; one dorsal vertebra has a reconstructed height of and a width of , and the are up to in width. In 2019, Paul estimated the total length of the dorsal vertebral column at and the width of the pelvis at 0.6 times the combined length of the dorsal and sacral vertebral column. The dorsals were (concave at the rear) as in other macronarian sauropods. The (excavations on the sides of the centra) were proportionally small and positioned in the front half of the centrum. The vertebrae were internally lightened by a complex pattern of numerous air-filled chambers. Such camellate bone is, among sauropods, especially pronounced in the largest and longest-necked species. In both the dorsal and sacral vertebrae, very large cavities measuring were present. The dorsal ribs were tubular and cylindrical in shape, in contrast with other titanosaurs. Bonaparte and Coria, in their 1993 description, noted the ribs were hollow, unlike those of many other sauropods, but later authors argued this hollowing could also have been due to erosion after the death of the individual. Argentinosaurus, like many titanosaurs, probably had six sacral vertebrae (those in the hip region), although the last one is not preserved. The centra of the second to fifth sacral vertebrae were much reduced in size and considerably smaller than the centrum of the first sacral. The sacral ribs curved downwards. The second sacral rib was larger than the other preserved sacral ribs, though the size of the first is unknown due to its incompleteness.
Because of their incomplete preservation, the original position of the known dorsal vertebrae within the vertebral column is disputed. Dissenting configurations were suggested by Bonaparte and Coria in 1993; Fernando Novas and Martín Ezcurra in 2006; and Leonardo Salgado and Jaime Powell in 2010. One vertebra was interpreted by these studies as the first, fifth or third; and another vertebra as the second, tenth or eleventh, or ninth, respectively. A reasonably complete vertebra was found to be the third by the 1993 and 2006 studies, but the fourth by the 2010 study. Another vertebra was interpreted by the three studies as being part of the rear section of the dorsal vertebral column, as the fourth, or as the fifth, respectively. In 1993, two articulated (still connected) vertebrae were thought to be of the rear part of the dorsal column but are interpreted as the sixth and seventh vertebrae in the two later studies. The 2010 study mentioned another vertebra that was not mentioned by the 1993 and 2006 studies; it was presumed to belong to the rear part of the dorsal column.