Giraffatitan

Giraffatitan (name meaning 'titanic giraffe') is a genus of sauropod dinosaur that lived during the late Jurassic Period (Kimmeridgian–Tithonian stages). It was originally named as an African species of Brachiosaurus (B. brancai), but this has since been changed. Giraffatitan was for many decades known as the largest dinosaur but recent discoveries of several larger dinosaurs prove otherwise; giant titanosaurians appear to have surpassed Giraffatitan in terms of sheer mass. Also, the sauropod dinosaur Sauroposeidon is estimated to be taller and possibly heavier than Giraffatitan. All size estimates for Giraffatitan are based on the specimen HMN SII, a subadult individual between 21.8–22.5 metres (72–74 ft) in length and about 12 meters (39 ft) tall. Mass estimates are varied and range from as little as 15 tonnes (17 short tons) to as much as 78.3 tonnes (86.3 short tons) but there is evidence supporting that these animals could grow larger; specimen HMN XV2, represented by a fibula 13% larger than the corresponding material on HMN SII, might have attained 26 metres (85 ft) in length or longer. Between 1914 and the 1990s, Giraffatitan was claimed to be the largest dinosaur known, (ignoring the possibly larger but lost Maraapunisaurus) and thus the largest land animal in history. In the later part of the twentieth century, several giant titanosaurians found appear to surpass Giraffatitan in terms of sheer mass. However, Giraffatitan and Brachiosaurus are still the largest brachiosaurid sauropods known from relatively complete material. All size estimates for Giraffatitan are based on the skeleton mounted in Berlin, which is partly constructed from authentic bones. These were largely taken from specimen HMN SII, a subadult individual between 21.8–22.46 metres (71.5–73.7 ft) in length and about twelve meters (forty feet) tall. The often mentioned length of 22.46 metres is by Werner Janensch, the German scientist who described Giraffatitan, and was the result of a simple adding error: the correct number should have been 22.16 metres. Mass estimates are more problematic and historically have strongly varied from as little as 15 tonnes (17 short tons) to as much as 78 tonnes (86 short tons). These extreme estimates are now considered unlikely due to flawed methodologies. There are also a large number of such estimations as the skeleton proved to be an irresistible subject for researchers wanting to test their new measuring methods. The first calculations were again made by Janensch. In 1935, he gave a volume of thirty-two cubic metres for specimen SII and of twenty-five cubic metres for specimen SI, a smaller individual. It is not known how he arrived at these numbers. In 1950, he mentioned a weight of forty tonnes for the larger skeleton. In 1962, Edwin Harris Colbert measured a volume of 86.953 m³. Presuming a density of 0.9, this resulted in a weight of 78,258 kilogrammes. Colbert had inserted a museum model, sold to the public, into sand and observed the volume displaced by it. Gregory S. Paul in 1988 assumed that the, in his opinion, unrealistically high number had been caused by the fact that such models used to be very bloated compared to the real build of the animal. In 1980, Dale Alan Russell e.a. published a much lower weight of 14.8 tonnes by extrapolating from the diameter of the humerus and the thighbone. In 1985, the same researcher arrived at twenty-nine tonnes by extrapolating from the circumference of these bones. In 1985, Robert McNeill Alexander found a value of 46.6 tonnes inserting a toy model of the British Museum of Natural History into water. More recent estimates based on models reconstructed from bone volume measurements, which take into account the extensive, weight-reducing airsac systems present in sauropods, and estimated muscle mass, are in the range of 23–40 tonnes (25–44 short tons). In 1988, G.S. Paul measured a volume of 36.585 m³ by inserting a specially constructed model into water. He estimated a weight of 31.5 tonnes, assuming a low density. In 1994/1995, Jan Peczkis calculated a weight of forty tonnes extrapolating from limb bone circumference. In 1995, Hans-Christian Gunga e.a. used a laser scan of the skeleton to build a virtual model from simple geometrical shapes, finding a volume of 74.42 m³ and concluding to a weight of 63 tonnes. In 2008, Gunga revised the volume, using more complex shapes, to 47.9 m³. Donald Henderson in 2004 employed a computer model that calculated a volume of 32.398 m³ and a weight of 25,789 kilogrammes. Newer methods use bone wall thickness. However, HMN SII is not the largest specimen known (an assertion supported by its subadult status) but HMN XV2, represented by a fibula 13% larger than the corresponding material on HMN SII, which might have attained 26 metres (85 ft) in length. Giraffatitan was a sauropod, one of a group of four-legged, plant-eating dinosaurs with long necks and tails and relatively small brains. It had a giraffe-like build, with long forelimbs and a very long neck. The skull had a tall arch anterior to the eyes, consisting of the bony nares, a number of other openings, and 'spatulate' teeth (resembling chisels). The first toe on its front foot and the first three toes on its hind feet were clawed. Traditionally, the distinctive high-crested skull was seen as a characteristic of the genus Brachiosaurus, to which Giraffatitan brancai was originally referred; however, it is possible that Brachiosaurus altithorax did not show this feature, since within the traditional Brachiosaurus material it is known only from Tanzanian specimens now assigned to Giraffatitan.