Giraffatitan

Giraffatitan Fossil range: Late Jurassic, 150–145 Ma PreЄ Є O S D C P T J K Pg N ↓
Skeleton on display in Berlin
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	†Sauropodomorpha
Infraorder:	†Sauropoda
Family:	†Brachiosauridae
Genus:	†Giraffatitan Paul, 1988
Species
G. brancai (Janensch, 1914) (type)

Giraffatitan, meaning "giraffe titan", 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). One of the largest animals known to have walked the earth, it has become one of the most famous of all dinosaurs.

Description

Skull, Naturkundemuseum Berlin

Giraffatitan was a sauropod, one of a group of four-legged, plant-eating dinosaurs with long necks and tails and relatively small brains. Unlike other families of sauropods, it had a giraffe-like build, with long forelimbs and a very long neck. Giraffatitan had "spatulate" teeth (resembling chisels), well-suited to its herbivorous diet. Its skull featured a number of holes, probably aiding weight-reduction. The first toe on its front foot and the first three toes on its hind feet were clawed.

Brachiosaurus has traditionally been characterized by its distinctive high-crested skull, though this is known only from Tanzanian specimens now assigned to Giraffatitan and may have been unique to that genus.

Size

For many decades, Giraffatitan was the largest dinosaur known. It has since been discovered that a number of giant titanosaurians (Argentinosaurus, for example) surpassed Giraffatitan in terms of sheer mass. More recently, another brachiosaurid, Sauroposeidon, was discovered; based on incomplete fossil evidence, it too is likely to have outweighed Giraffatitan.

Giraffatitan is the largest dinosaur known from a relatively complete fossilized skeleton. The most complete specimens, including the Giraffatitan in the Humboldt Museum of Berlin (excavated in Tanzania)—the tallest mounted skeleton in the world—are members of the species G. brancai.

Based on a complete composite skeleton, G. brancai attained 25 metres (82 ft) in length and was probably able to raise its head about 13 metres (43 ft) above ground level.

Size comparison with a human

Historically, G. brancai has been estimated to have weighed as little as 15 tonnes (17 short tons) and as much as 78.26 tonnes (86.27 short tons).^[1][2] However these extreme estimates are now considered unlikely. The smaller, 15t estimate (by Dale Russell and colleagues in 1980) was based on scaling up limb bones based on smaller specimens, rather than a body model, and the larger, 78t estimate (by Edwin Harris Colbert in 1962) was based on an outdated and overweight model. More recent estimates based on models reconstructed from bone volume measurements (which take into account the extensive, weight-reducing air sac systems present in sauropods) and estimated muscle mass are in the range of 23 tonnes (25 short tons) to 37 tonnes (41 short tons).^[3][4][5]

Classification

Artist's impression

Giraffatitan brancai was originally classified as a species of Brachiosaurus when it was described by Janensch in 1914. It is known from five partial skeletons, including at least three skulls and some limb bones, which were recovered near Lindi, Tanzania in the early 1900s. It lived from 145 to 150 million years ago, during the Kimmeridgian to Tithonian ages of the Late Jurassic period. More advanced than B. altithorax, it had longer limbs, a skull with a taller, shorter nasal arch or "crest", a shorter muzzle, and longer limbs. Due to these differences, scientists have suggested that it should be split into its own genus, Giraffatitan.

In 1988, Gregory S. Paul noted that the African form (on which most popular depictions of Brachiosaurus were based) showed significant differences from the North American Brachiosaurus, especially in the proportions of its trunk vertebrae and in its more gracile build. Paul used these differences to create a subgenus he named Brachiosaurus (Giraffatitan) brancai. In 1991, George Olshevsky asserted that these differences are enough to place the African brachiosaurid in its own genus, simply Giraffatitan.^[6]

Giraffatitan scapula at the Museum für Naturkunde, Berlin

Adding further differences between the two species was the description in 1998 of a North American Brachiosaurus skull. This skull, which had been found nearly a century earlier (it is the skull Marsh used on his early reconstructions of Brontosaurus), is identified as "Brachiosaurus sp." and may well belong to B. altithorax. The skull is more camarasaur-like than the distinctive short-snouted and high-crested skull of Giraffatitan.^[7]

The classification of Giraffatitan as a separate genus was not widely followed by other scientists at first, as it was not supported by a rigorous comparison of both species. However, a detailed comparison was published by Michael Taylor in 2009. Taylor showed that "Brachiosaurus" brancai differed from B. altithorax in almost every fossil bone that could be compared, in terms of both size, shape, and proportion, finding that the placement of Giraffatitan in a separate genus was valid.^[3]

Paleobiology

Brain

Like other sauropods, Giraffatitan had a relatively small brain, even when its massive body size is taken into account. A 2009 study calculated its brain-to-body mass ratio (a rough estimate of possible intelligence) at a low 0.62 or 0.79, depending on the size estimate used. Giraffatitan is also similar to other sauropods in having an enlargement of the spinal chord above the hips, which some older sources misleadingly referred to as a "second brain".^[8]

Metabolism

If Giraffatitan was endothermic (warm-blooded), it would have taken an estimated ten years to reach full size, if it were instead poikilothermic (cold-blooded), then it would have required over 100 years to reach full size.^[9] As a warm-blooded animal, the daily energy demands of Giraffatitan would have been enormous; it would probably have needed to eat more than ~182 kg (400 lb) of food per day. If Giraffatitan was fully cold-blooded or was a passive bulk endotherm, it would have needed far less food to meet its daily energy needs. Some scientists have proposed that large dinosaurs like Giraffatitan were gigantotherms.^[10]

Environment and behavior

Grown and juvenile Giraffatitan brancai

The nostrils of Giraffatitan, like the huge corresponding nasal openings in its skull, were long thought to be located on the top of the head. In past decades, scientists theorized that the animal used its nostrils like a snorkel, spending most of its time submerged in water in order to support its great mass. The current consensus view, however, is that Giraffatitan was a fully terrestrial animal. Studies have demonstrated that water pressure would have prevented the animal from breathing effectively while submerged and that its feet were too narrow for efficient aquatic use. Furthermore, new studies by Lawrence Witmer (2001) show that, while the nasal openings in the skull were placed high above the eyes, the nostrils would still have been close to the tip of the snout (a study which also lends support to the idea that the tall "crests" of brachiosaurs supported some sort of fleshy resonating chamber).

History of discovery

Native excavators with Giraffatitan bones in German East Africa, near the city of Lindi, 1909

Giraffatitan brancai was first named and described by German paleontologist Werner Janensch in 1914 as Brachiosaurus brancai, based on several good specimens from the Tendaguru formation in what is now Tanzania.^[11]

In culture

Mounted skeleton of Giraffatitan before it was remounted

A famous specimen of Giraffatitan brancai mounted in Museum für Naturkunde Berlin is one of the largest, and in fact the tallest, mounted skeletons in the world, as certified by the Guinness Book of Records. Beginning in 1909, Werner Janensch found many additional G. brancai specimens in Tanzania, Africa, including some nearly complete skeletons, and composited the elements into the mounted skeleton seen today.

References

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