Antarctosaurus

Taxobox
name = "Antarctosaurus"
fossil_range = Late Cretaceous

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image width = 200px
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Sauropodomorpha
infraordo = Sauropoda
unranked_familia = Titanosauria
familia = Antarctosauridae
familia_authority = Olshevsky, 1978
genus = "Antarctosaurus"
genus_authority = von Huene, 1929
subdivision_ranks = Species
subdivision =
*"A. wichmannianus" (type)
*?"A. giganteus" von Huene, 1929
*"A." jaxartensis" Riabinin, 1939
*"A." brasiliensis" Arid & Vizotto, 1971

"Antarctosaurus" (pronEng|ænˌtɑrktəˈsɔːrəs; 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."Antarctosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. "The Age of Dinosaurs". Publications International, LTD. p. 125. ISBN 0-7853-0443-6.]

Description

"Antarctosaurus" was a huge quadrupedal herbivore with a long neck and tail. It was possibly armored. 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 "anti-" meaning 'opposite of', "arktos" meaning 'north' and "sauros" meaning 'lizard'. The generic name refers to the animal's reptilian nature and its geographical location on a southern continent.

pecies 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, F. 1929. Los saurisquios y ornitisquios del Cretacéo Argentino. "Anales del Museo de La Plata" (series 3) 3: 1–196. [In Spanish] ]

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.Mazzetta, G.V., Christiansen, P., Fariña, R.A. 2004. Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs. "Historical Biology". 16: 71-83.]

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".Upchurch, P. 1999. The phylogenetic relationships of the Nemegtosauridae. "Journal of Vertebrate Paleontology" 19: 106–125.] Sereno, P.C., Beck, A.L., Dutheil, D.B., Larsson, H.C.E, Lyon, G.H., Moussa, B., Sadleir, R.W., Sidor, C.A., Varricchio, D.J., Wilson, G.P., Wilson, J.A. 1999. Cretaceous sauropods from the Sahara and the uneven rate of skeletal evolution among dinosaurs. "Science" 286: 1342–1347.] Wilson, J.A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. "Zoological Journal of the Linnean Society" 136: 217–276.] 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. Apesteguía, S. 2004. "Bonitasaura salgadoi" gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia. "Naturwissenschaften" 91: 493–497.] Wilson, J.A. 2005. Redescription of the Mongolian sauropod "Nemegtosaurus mongoliensis" Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. "Journal of Systematic Palaeontology" 3(3): 283–318.]

"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.von Huene, F. & Matley, C.A. 1933. Cretaceous Saurischia and Ornithischia of the central provinces of India. "Palaeontologia Indica" 21: 1–74.] 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.Riabinin, A.N. 1939. [The Upper Cretaceous vertebrate fauna of south Kazakhstan I. Reptilia. Pt. 1 Ornithischia] . "Tsentral. Nauchno-issled. Geol. Inst. Trudy". 118: 1-40. [In Russian] ] 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.Arid, F.M. & Vizotto, L.D. 1971. "Antarctosaurus brasiliensis", um novo saurópode do Crétaceo superiordo sul do Brasil. "An. Cong. Bras. Geol." 1971: 297-305. [In Portuguese] ] This species is also considered a "nomen dubium".Upchurch, P., Barrett, P.M, & Dodson, P. 2004. Sauropoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). "The Dinosauria" (2nd Edition). Berkeley: University of California Press. Pp. 259-322.]

References

External links

* [http://dml.cmnh.org/2002Nov/msg00106.html Post] on the [http://dml.cmnh.org Dinosaur Mailing List] detailing the various species of "Antarctosaurus" and the remains assigned to them.