Bruhathkayosaurus (/bruːˌhæθkeɪoʊˈsɔːrəs/; meaning "huge-bodied lizard") is a genus of dinosaur found in India. The fragmentary remains were originally described as a theropod but later publications listed it as a sauropod. Estimates by researchers exceed those of the titanosaur Argentinosaurus, as longer than 35 metres (115 ft) and weighing over 80-200 tons. All the estimates are based on the dimensions of the fossils described in Yadagiri and Ayyasami's 1987 paper, which announced the find. In 2017 it was reported that the original fossils had disintegrated and no longer exist.
Yadagiri & Ayyasami, 1987
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 Sanskrit word Bruhathkaya (bṛhat बृहत्, 'huge, heavy' and kāya, काय 'body'), plus the Greek sauros (lizard).
The monsoon season combined with the sands and clays of the Kallemedu Formation creates water saturated fossils which are very friable. During the dry season expansion during the day and contraction during the night can cause fossils to split apart. This makes bones poorly preserved and can be impossible to extract without breaking apart. In 2017, Galton and Ayyasami reported that the Bruhathkayosaurus fossils started to disintegrate inside their field jackets before reaching the Geological Survey of India (GSIH) and no longer exist.
The type species, Bruhathkayosaurus matleyi, is based on the holotype specimen GSI PAL/SR/20, which was described by Yadagiri and Ayyasami in 1987 (not 1989, as some sources indicate). It was originally classified as a carnosaur (like Allosaurus), of an uncertain position (incertae sedis). However, Chatterjee (1995) re-examined the remains and demonstrated that Bruhathkayosaurus is actually a titanosaur sauropod. Later studies have listed Bruhathkayosaurus as an indetermiate sauropod or as a nomen dubium.
The original publication described little in the way of diagnostic characteristics and was only supported by a few line drawings and photographs of the fossils as they lay in the ground. This led to online speculation by researchers 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 only known remains of Bruhathkayosaurus have been lost so the validity of the genus and any size estimates are questionable.
According to the published description, the shin bone (tibia) of Bruhathkayosaurus was 2 m (6.6 ft) long. This is 29 percent larger than the tibia of Argentinosaurus, which is only 1.55 m (5.1 ft) long. The fragmentary femur was similarly huge; across the distal end, it measured 75 cm (2.46 ft), 33% larger than the femur of Antarctosaurus giganteus, which measures 56 cm (1.84 ft). The illium measured 1.2 m (3.9 ft) in length.
No total body size estimates for Bruhathkayosaurus have been published, but paleontologists and researchers have posted tentative estimates on the Internet. In a post from June 2001, Mickey Mortimer estimated that Bruhathkayosaurus could have reached 40–44 m (131–144 ft) in length and might have weighed 175–220 tons, but in later posts retracted these estimates, reducing the estimated length of Bruhathkayosaurus to 28–34 m (92–112 ft), and declined to provide a new weight estimate, describing the older weight 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 126 metric tons (139 short tons).
By comparison, the titanosaur Argentinosaurus is estimated to have reached 35 m (115 ft) in length, and to have weighed 80–100 tons. 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 and the record-holder blue whale was recorded at 173 tonnes (190 short tons).
Another poorly known sauropod that shares similar size estimates to Bruhathkayosaurus is Maraapunisaurus fragillimus, which was based on a now-missing dorsal vertebra. In 2006 Carpenter used Diplodocus as a guide and estimated Maraapunisaurus to be 58 m (190 ft) in length and weigh only about 122.4 metric tons (130 short tons). In 2018, however, Carpenter estimated Maraapunisaurus to be 30–32 m (98–105 ft) in length based upon comparisons with rebbachisaurids.
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