Temporal range: Late Cretaceous, 70Ma
Yadagiri & Ayyasami, 1989
Bruhathkayosaurus (//; meaning "huge bodied lizard") is a dinosaur that some researchers claim to 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.
The authors originally classified the dinosaur as a theropod, a member of a large group of bipedal, mostly carnivorous dinosaurs that includes Tyrannosaurus, but several unpublished opinions beginning in 1995 suggested that the remains actually belonged to a sauropod (probably a titanosaur), a member of a very different group of quadrupedal, herbivorous dinosaurs with long necks and tails. In 2006, the first published reference to Bruhathkayosaurus as a sauropod appeared in a survey of Malagasy vertebrates by David Krause and colleagues.
Until the remains are properly described, the validity of the genus and any size estimates will be questionable. It is possible that the only known remains of Bruhathkayosaurus have been lost to monsoon flooding. Thus the only remaining evidence is likely the very simple and indistinct line-drawings of the bones.
Bruhathkayosaurus was found near the southern tip of India, specifically in the Tiruchirappalli 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 (part of a vertebra, specifically a platycoelous caudal centrum). The remains were originally classified as belonging to a carnosaur. The name chosen, Bruhathkayosaurus, is derived from bruhath (South Indian transliteration of Sanskrit bṛhat बृहत्, 'huge, heavy') and kāya (काय 'body'), plus the Greek sauros (lizard).
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. It was later recognized as a sauropod.
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.
According to the published description, the shin bone (tibia) of Bruhathkayosaurus is 2 m (6.6 ft) long. This is 29 percent larger than the tibia of Argentinosaurus, which is only 1.55 m (5.08 ft) long. The fragmentary femur is similarly huge, across the distal end, it measures 75 cm (2.5 ft), 33% larger than the femur of Antarctosaurus giganteus, which measures 56 cm (1.8 ft).
No total body size estimates for Bruhathkayosaurus have been published, but paleontologists and researchers have posted tentative estimates on the Internet. One early estimate by Mickey Mortimer estimated that Bruhathkayosaurus could have reached 40–44 m (130–145 ft) in length and to have weighed 175–220 tons. However, Mortimer later retracted these estimates, reducing his estimated length of Bruhathkayosaurus to 28–34 m (90–110 ft), and declined to provide a new weight estimate, describing the older mass estimates as inaccurate. In a May 2008 article for the weblog Sauropod Vertebra Picture of the Week, paleontologist Matt Wedel used a comparison with Argentinosaurus and calculated the weight of Bruhathkayosaurus at up to 139 tons.
By comparison, the titanosaur Argentinosaurus is estimated to have reached 39.7 m (130 ft) in length, and to have weighed 60-90 tons. Another huge titanosaurid, Paralititan, was probably 32 m (105 ft) long, and weighed 59-80 tons.  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.
If the size estimates for Bruhathkayosaurus are accurate it would be similar in size to the Blue Whale. Mature Blue Whales can reach 30 m (98 ft) in length, which is a little shorter than Bruhathkayosaurus, but the record-holder Blue Whale weighed in at 176 tons, which is probably heavier than Bruhathkayosaurus.
Among the dinosaurs, only another poorly known specimen may approach or exceed Bruhathkayosaurus in size. Edward Drinker Cope's Amphicoelias fragillimus is estimated to have been longer, on the order of 58 m (190 ft) in length, but it was a slender diplodocid, weighing only about 122 tons. However, the only bone recovered (a massive vertebra) is now missing, and only a description and drawing of the specimen remain.
- Yadagiri, P. and Ayyasami, K. (1989). "A carnosaurian dinosaur from the Kallamedu Formation (Maestrichtian horizon), Tamilnadu." In M.V.A. Sastry, V.V. Sastry, C.G.K. Ramanujam, H.M. Kapoor, B.R. Jagannatha Rao, P.P. Satsangi, and U.B. Mathur (eds.), Symposium on Three Decades of Development in Palaeontology and Stratigraphy in India. Volume 1. Precambrian to Mesozoic. Geological Society of India Special Publication, 11(1): 523-528.
- Krause, D.W., O'Connor, P.M., Curry Rogers, K., Sampson, S.D., Buckley, G.A., and Rogers, R.R. (2006). "Late Cretaceous terrestrial vertebrates from Madagascar: Implications for Latin American biogeography." Annals of the Missouri Botanical Garden, 93(2): 178-208.
- Schneiderman, P. (1994). "Report on the initial description". Dinosaur Mailing List
- Mortimer, M. (2001), "Re: Bruhathkayosaurus", discussion group, The Dinosaur Mailing List, 19 June 2001. Accessed 23 May 2008.
- Mortimer, M. (2004), "Re: Largest Dinosaurs", discussion group, The Dinosaur Mailing List, 7 September 2004. Accessed 23 May 2008.
- Mortimer, M. (2001), "Titanosaurs too large?", discussion group, The Dinosaur Mailing List, 12 September 2001. Accessed 23 May 2008.
- Wedel, M. "SV-POW! showdown: sauropods vs whales." [Weblog entry.] Sauropod Vertebra Picture of the Week. 20 May 2008. Accessed 23 May 2008.
- Smith, J.B.; Lamanna, M.C.; Lacovara, K.J.; Dodson, P.; Smith, J.R.; Poole, J.C.; Giegengack, R.; Attia, Y. (2001). "A giant sauropod dinosaur from an Upper Cretaceous mangrove deposit in Egypt". Science 292 (5522): 1704–1706. doi:10.1126/science.1060561. PMID 11387472.
- J. Calambokidis and G. Steiger (1998). Blue Whales. Voyageur Press. ISBN 0-89658-338-4.
- "What is the biggest animal ever to exist on Earth?". How Stuff Works. Retrieved 2007-05-29.
- Carpenter, K. (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus." In Foster, J.R. and Lucas, S.G., eds., 2006, Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36: 131–138.
- Report on the initial description from the Dinosaur Mailing List.