Argentinosaurus

Argentinosaurus (meaning "lizard from Argentina") is a genus of giant sauropod dinosaur from the Early Cretaceous of what is now Argentina. It belongs to Titanosauria, the main sauropod group of the Cretaceous. Though known only from fragmentary fossils, it was one of the largest land animals ever, reaching a certain length and weight.

The first bone—now thought to be a fibula—was found in 1987 by a farmer on his farm near Plaza Huincul, Neuquén Province. Believing it was petrified wood, he alerted the local Museo Carmen Funes, whose staff excavated and stored it. In early 1989, Argentine palaeontologist José Bonaparte led a larger excavation at the site, using pneumatic hammers to separate bones from very hard rock. This yielded seven back vertebrae, the underside of the sacrum (including the first to fifth sacral vertebrae and some sacral ribs), and part of a rib. These became the holotype specimen, MCF-PVPH 1. Bonaparte presented the find in 1989 at a conference in San Juan. The formal description and naming of the genus and species *Argentinosaurus huinculensis* (the species name referring to Plaza Huincul) was published in 1993 by Bonaparte and Rodolfo Coria. The 1987 limb bone was originally described as a tibia but was reidentified as a left fibula in 2004. In 1996, Bonaparte assigned a complete femur from the same locality to the genus, though it was crushed front-to-back during fossilization. A second femur, only the shaft preserved, is housed in the La Plata Museum. As of 2019, it remained uncertain whether either femur actually belonged to *Argentinosaurus*.

Because the remains are so fragmentary, interpreting them is difficult. Debate centers on where the recovered vertebrae fit in the spinal column and whether they had extra joints that would have strengthened the spine. A computer model of the skeleton and muscles estimated a maximum speed of 7.2 km/h (5 mph) using a pace gait. The fossils come from the Huincul Formation, deposited during the Albian stage, which also contains a diverse dinosaur fauna including the giant theropod *Mapusaurus*.

Estimating the animal's size is challenging. Palaeontologists compare the known bones to those of smaller, more complete relatives and scale them up. Mass can be estimated from bone measurements or model volumes. Reconstructions have varied: Gregory Paul in 1994 gave a length estimate; Bonaparte and Coria in 1994 suggested a hind limb length of a certain value, a trunk length, and an overall body length; Kenneth Carpenter in 2006 used *Saltasaurus* as a guide; Jorge Calvo and colleagues in 2008 used *Futalognkosaurus* to estimate a length of less than a certain figure; and in 2013, William Sellers and colleagues measured the skeletal mount at the Museo Carmen Funes to arrive at a length and shoulder height. That same year, Scott Hartman noted that because *Argentinosaurus* was so incomplete, its exact size remained uncertain.