Bruhathkayosaurus
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? Bruhathkayosaurus Conservation status: Fossil
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| ?Bruhathkayosaurus matleyi ( Yadagiri & Ayyasami, 1989) |
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Bruhathkayosaurus (brew-HATH-kah-yo-SORE-us, meaning "huge bodied lizard") might have been the largest dinosaur ever lived.
The accuracy of this claim, however, has been mired in controversey 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 the 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 the Brachiosaurus.
Until the remains are properly described, the validity of any estimates will be questioned.
Largest ever?
As a sauropod, the Bruhathkayosaurus is estimated to reach 40 m (130 ft) or 44.1 m (145 ft) in length, 14 m (46 ft) in height, and to weigh from 175 to 220 t (190 to 240 tons). By comparison, the Argentinosaurus is estimated to reach 34.6 m (114 ft) in length, and to weigh from 80 to 100 t (90 to 110 tons). Another huge titanosaurid, the 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 (100 ft) in length, which is shorter than the 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 the Argentinosaurus.
When the Bruhathkayosaurus was still considered to be a theropod, it was estimated to be 18 to 20 m (60 to 65 ft) long, and to weigh from 11 to 14 t (12 to 15 tons). This is substantially larger than even the largest known terrestrial carnivores, like the Giganotosaurus, Tyrannosaurus, and Carcharodontosaurus. None of these giant predators are believed to exceed 12 to 15 m (40 to 50 ft) in length, and 6 to 8 t (6.5 to 9 tons) in mass.
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. But extrapolation is just 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 lengths of the giant titanosaurs considerably. The Bruhathkayosaurus was reduced to 28 to 34 m (90 to 110 ft) in length, the Argentinosaurus was reduced to 22 to 26 m (70 to 85 ft), and the Paralititan was reduced to 20 to 24 m (65 to 80 ft). While not provided, the estimated weights would also be reduced. For instance, if the estimated mass of the Argentinosaurus were reduced to 73 t (80 tons), then the Bruhathkayosaurus might only weigh 157 t (173 tons).
However, regardless of which estimate is used the Bruhathkayosaurus is 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 the 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 the Bruhathkayosaurus is incomplete, it is extrapolated to be 2.34 m (7 ft, 8 in) long. This is 30 percent larger the humerus of the Argentinosaurus, which is 1.81 m (5 ft, 11 in) long.
Classification
The Bruhathkayosaurus genus has only one known species, the 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 the Allosaurus) of an unknown (incertae sedis) family, which is a group of theropods. 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 the Sauroposeidon initially believed their find to be fossilized tree trunks.
The name chose, Bruhathkayosaurus, is derived from the Sanskrit bruhath (बृहतः)(huge, or heavy) and kaya (काया) (body); and the Greek sauros (lizard).
Discovery
The 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).