Bruhathkayosaurus

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Bruhathkayosaurus ([bɹuˈhæθ.kej.joˌsɔɹ.əs], meaning 'huge bodied lizard') might have been the largest dinosaur that ever lived.

The accuracy of this claim, however, has been mired in controversy and debate. All the estimates are based on Yadagiri and Ayyasami's 1989 paper, which announced the find.

Their technical description is so poor that the authors originally classified the dinosaur as a theropod, a member of a large group of bipedal, carnivorous dinosaurs that includes Tyrannosaurus, but a review of their data in 1995 revealed that the remains actually belonged to a sauropod (specifically, a titanosaurid), a member of a very different group of quadrupedal, herbivorous dinosaurs with long necks and tails, like Brachiosaurus.

Until the remains are properly described, the validity of any estimates will be questioned.

[edit] Largest ever?

As a sauropod, Bruhathkayosaurus is estimated to have reached 40 m (130 ft) or 44.1 m (145 ft) in length, 14 m (46 ft) in height, and to have weighed from 175 to 220 t (190 to 240 tons). By comparison, Argentinosaurus is estimated to have reached 34.6 m (114 ft) in length, and to have weighed from 80 to 100 t (90 to 110 tons). Another huge titanosaurid, Paralititan, was probably 31.9 m (105 ft) long, and weighed 65 to 80 t (72 to 88 tons).

The only real competition is the blue whale. The largest on record reached an estimated 33.5 m (110 ft) in length, which is shorter than Bruhathkayosaurus; but was equally massive, weighing in at 177 t (195 tons).

Among the dinosaurs, only the most dubious contenders even come close. Edward Drinker Cope's Amphicoelias fragillimus would have been longer, reaching 56 to 62 m (185 to 200 ft) in length, but it was a slender diplodocid, weighing only 125 to 170 t (140 to 185 tons). Unfortunately, the only bone recovered apparently crumbled to dust over a hundred years ago. There is also an unknown sauropod from Broome, Australia, but estimates are difficult because it is known only from a fossilized trackway. Another as-yet undescribed titanosaurid from South America is only a little larger than Argentinosaurus.

When Bruhathkayosaurus was still considered to be a theropod, it was estimated to have been 18 to 20 m (60 to 65 ft) long, and to have weighed from 11 to 14 t (12 to 15 tons). This is larger than even the largest known terrestrial carnivore, Spinosaurus, which reached at least 16-17 meters (53-56ft) in length and 9 tons in mass.

[edit] Estimated uncertainty

All of these sauropods are known only from partial or fragmentary remains, so the size estimates are uncertain. Length is calculated by comparing existing bones to the bones of similar dinosaurs, which are known from more complete skeletons and scaling them up isometrically. However, such extrapolation can never be more than an educated guess and the length of the tail, in particular, is often hard to judge. Determining mass is even more difficult, because little evidence of soft tissues survives in the fossil record. In addition, isometric scaling is based on the assumption that body proportions remain the same, which is not necessarily the case. In particular, the proportions of the titanosaurs are not well known, due to a limited number of relatively complete specimens.

It is also worth noting that at least one recent estimate reduces the suggested lengths of the giant titanosaurs considerably. The length of Bruhathkayosaurus was reduced to 28 - 34 m (90 - 110 ft), Argentinosaurus was reduced to 22 - 26 m (70 - 85 ft) and Paralititan was reduced to 20 - 24 m (65 - 80 ft). While not provided, the estimated weights would also be reduced. For instance, if the estimated mass of Argentinosaurus were reduced to 73 t (80 tons), then Bruhathkayosaurus might only have weighed 157 t (173 tons).

However, regardless of which estimate is used, Bruhathkayosaurus was still substantially larger than the other giant sauropods. If the published material is correct, its shin bone (tibia) is 2 m (6 ft, 7 in) long. This is 29 percent larger than the tibia of Argentinosaurus, which is only 1.55 m (5 ft, 1 in) long.

Comparing the bones in the upper forelimb gives a similar result. While the humerus of Bruhathkayosaurus is incomplete, it is extrapolated to have been 2.34 m (7 ft, 8 in) long. This is 30 percent larger than the humerus of Argentinosaurus, which is 1.81 m (5 ft, 11 in) long.

[edit] Classification

The Bruhathkayosaurus genus has only one known species, Bruhathkayosaurus matleyi. The species is represented by the holotype specimen GSI PAL/SR/20, which was described by Yadagiri and Ayyasami in 1989 (not 1987, as some sources indicate).

It was originally classified as a carnosaur (like Allosaurus), of an unknown (incertae sedis) family. In 1995, Chatterjee reclassified it as a titanosaur. The reclassification was based on the massive size of the limbs and the structure of the pelvis.

The original publication described little in the way of diagnostic characteristics and was only supported by a few line drawings. This has led to speculation that the bones might actually be petrified wood, akin to the way the original discoverers of Sauroposeidon initially believed their find to be fossilized tree trunks.

The name chosen, Bruhathkayosaurus, is derived from the Sanskrit bruhath (बृहतः)(huge, or heavy) and kaya (काया) (body); and the Greek sauros (lizard).

[edit] Discovery

Bruhathkayosaurus was found near the southern tip of India, specifically in the Tiruchirapalli district of Tamil Nadu, to the northeast of Kallamedu village. It was recovered from the rocks of the Kallemedu Formation, which are dated to the Maastrichtian faunal stage of the late Cretaceous period. It lived toward the end of Mesozoic era, about 70 million years ago.

The fossilized remains include hip bones (the ilium and ischium), part of a leg bone (femur), a shin bone (tibia), a forearm (radius) and a tail bone (a vertebrae, specifically a platycoelous caudal centrum).

[edit] Further reading

• A carnosaurian dinosaur from the Kallamedu Formation (Maastrichtian horizon), Tamilnadu, by P. Yadagiri and K. Ayyasami, edited by in Sastry, M.V.A. and others. 1989. Symposium on Three Decades of Development in Palaeontolgy and Stratigraphy in India: Geological Survey of India Special Publications, volume 11, issue 1, pages 523 to 528.

[edit] External links

• "Bruhathkayosaurus ". DinoData.

• What were the longest/heaviest dinosaurs?, by Mike Taylor.
• Earthshakers from UK Dinosaurs.
• Bruhathkayosaurus: "huge body lizard", by T. Mike Keesey from The Dinosauricon. (technical)
• Discussion on the Dinosaur Mailing List: [1] [2] [3] [4].