Antarctosaurus

Antarctosaurus (pron.: / æ n ˌ t ɑr k t ɵ ˈ s ɔr ə s /; meaning "southern lizard") is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now South America. The type species, A. wichmannianus, was described by prolific German paleontologist Friedrich von Huene in 1929, who also described a second species in 1929. Three additional species of Antarctosaurus have been named since then. Later studies indicate that none of these pertain to Antarctosaurus.

Antarctosaurus was very large, even for a dinosaur. Scientists still have much to learn about Antarctosaurus, as a complete skeleton remains elusive.

Description

Antarctosaurus was a huge quadrupedal herbivore with a long neck and tail. It was possibly armoured. As Antarctosaurus is not known from a complete skeleton and tail lengths are highly variable among sauropods, the true size of these animals is hard to extrapolate. The type species may have been over 60 feet (18 meters) long, and a second species may have been one of the largest land animals ever. Antarctosaurus may have been as tall as 15 feet at the shoulder.

Etymology

Remains of this dinosaur were first mentioned in print in 1916, although they were not fully described and named until a 1929 manuscript written by paleontologist Friedrich von Huene. Antarctosaurus does not refer to the continent of Antarctica, since it was first found in Argentina, although it does have the same derivation, from the Greek words αντι-, anti- meaning 'opposite of', αρκτός, arktos meaning 'north' and σαυρος, sauros meaning 'lizard'. The generic name refers to the animal's reptilian nature and its geographical location on a southern continent.

Species of Antarctosaurus

Several species have been assigned to Antarctosaurus over the years, probably incorrectly in most cases.

Antarctosaurus wichmannianus

This is the type species of the genus, named in 1929 after the discoverer of its remains, geologist R. Wichmann.

Von Huene used the name A. wichmannianus to describe a large assemblage of bones, which are now considered to come from the Anacleto Formation in Río Negro Province of Argentina, which is considered to be early Campanian in age or about 83-80 million years old. Several skull fragments were described, including a braincase and a mandible (lower jaw). Other bones referred to this dinosaur include neck and tail vertebrae, ribs, and numerous limb bones. One femur (thigh bone) is over 6 feet (1.85 meters) tall, which has been used to extrapolate a mass of about 34 metric tonnes, or nearly 75,000 pounds.

These bones were for the most part not associated with each other but scattered throughout the formation. Consequently, many scientists believe that they may not all belong to the same type of animal. In particular, the very square lower jaw has frequently been suggested to belong to a rebbachisaurid sauropod similar to Nigersaurus. However the jaw of Bonitasaura is similar in overall shape and is clearly associated with titanosaur skeletal remains, indicating that the lower jaw may belong to Antarctosaurus wichmannianus after all. The back of the skull and the remainder of the skeleton are usually regarded as titanosaurian, although they do not necessarily belong to the same type of titanosaur. A. wichmannianus (minus the lower jaw) has been regarded as a lithostrotian, a group which includes armored titanosaurs, although no armor scutes were associated with its remains. This species has also been regarded as a possible nemegtosaurid titanosaur.

Antarctosaurus giganteus

Von Huene named a second species of Antarctosaurus in 1929, which he called A. giganteus because of its enormous size. Very few remains are known of this species and it is regarded as a nomen dubium by some. The most famous of these bones are two gigantic femora, which are among the largest of any known sauropod. They measure about 7.75 feet (2.35 meters) in length. Extrapolating from the size of these bones has led to a mass estimate of approximately 69 metric tonnes (152,000 pounds) in one study, just a little smaller than the gigantic Argentinosaurus, which at nearly 73 metric tonnes (160,000 pounds) would have been the heaviest known land animal of all time.

The bones mentioned above were recovered in Neuquén Province of Argentina, from the Plottier Formation, which dates to the late Coniacian stage of the Late Cretaceous Period, or about 87 to 85 million years ago. The Plottier, like the younger Anacleto, is a member of the Neuquén Group.

As so little is known of this animal, and because the material assigned to A. wichmannianus is so confused, A. giganteus cannot be confidently assigned to the genus Antarctosaurus at this time.

"Antarctosaurus" septentrionalis

In 1933, von Huene and Charles Matley described another species from India. This species does preserve important anatomical information but does not belong to Antarctosaurus. It was renamed Jainosaurus in 1994.

"Antarctosaurus" jaxartensis

A single femur from Kazakhstan forms the basis of this species, which was named by Soviet paleontologist Anatoly Riabinin in 1939. It is regarded as a nomen dubium today but is almost certainly not a species of the South American Antarctosaurus.

"Antarctosaurus" brasiliensis

Remains of this dinosaur, including two fragmentary limb bones and a partial vertebra, were found in the Bauru Formation of Brazil and described by Arid and Vizzotto in 1971. This species is also considered a nomen dubium.