Giraffatitan, meaning "giant giraffe", is a genus of sauropod dinosaur that lived during
the late Jurassic Period. It was originally named as an African species of Brachiosaurus.
Giraffatitan is one of the largest animals known to have walked the earth.
Description
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. The first toe on its
front foot and the first three toes on its hind feet were clawed.
Traditionally, the distinctive high-crested skull has been seen as a characteristic of
the genus Brachiosaurus to which Giraffatitan brancai was originally referred, but because
within the traditional Brachiosaurus material it is known only from Tanzanian specimens
now assigned to Giraffatitan, it is possible that Brachiosaurus altithorax did not show
this feature. Size
For many decades, Giraffatitan was claimed to be the largest dinosaur known, but in the
later part of the 20th century several giant titanosaurians appear to have surpassed Giraffatitan
in terms of sheer mass. However, Giraffatitan, along with Brachiosaurus are still the largest
dinosaurs known from relatively complete material. All size estimates for Giraffatitan are based
on the specimen HMN SII, a subadult individual between 21.8–22.5 metres in length. Mass
estimates are more problematic and historically have varied from as little as 15 tonnes to
as much as 78 tonnes. These extreme estimates are now considered unlikely due to flawed
methodologies. 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 23–37 tonnes. However, HMN SII is not the
largest specimen known but HMN XV2, represented by a tibia 13% larger than the corresponding
material on HMN SII, which might have attained 26 metres in length.
History and classification
Giraffatitan brancai was first named and described by German paleontologist Werner Janensch in
1914 as Brachiosaurus brancai, based on several specimens recovered between 1909 and 1912
from the Tendaguru formation near Lindi, in what was then German East Africa, today Tanzania.
It is known from five partial skeletons, including three skulls and numerous fragmentary remains
including skull material, some limb bones, vertebrae and teeth. It lived from 145 to
150 million years ago, during the Kimmeridgian to Tithonian ages of the Late Jurassic period.
A famous specimen of Giraffatitan brancai mounted in Museum für Naturkunde 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 used them to
create the composite mounted skeleton seen today.
In 1988, Gregory S. Paul noted that Brachiosaurus brancai 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 brancai. In 1991, George Olshevsky asserted that these differences were enough
to place the African brachiosaurid in its own genus, simply Giraffatitan.
Further differences between the African and North American forms came to light with the
description in 1998 of a North American Brachiosaurus skull. This skull, which had been found nearly
a century earlier, is identified as "Brachiosaurus sp." and may well belong to B. altithorax.
The skull is closer to Camarasaurus in some features such as the form of the front teeth
and more elongated and less hollowed-out on top than the distinctive short-snouted and
high-crested skull of Giraffatitan. 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. Taylor found
evidence of a sister relationship between Giraffatitan and Brachiosaurus, although his
analysis omitted other Brachiosaurids. A more recent study on Titanosauriform sauropods
by D'Emic places Giraffatitan as sister to a clade containing Brachiosaurus and a tritomy
of Abydosaurus, Cedarosaurus, and Venenosaurus as shown below:
Paleobiology Brain
Giraffatitan's brain measured about 300 cm³, which, like those of other sauropods, was
small compared to its massive body size. A 2009 study calculated its brain-to-body mass
ratio at a low 0.62 or 0.79, depending on the size estimate used. Giraffatitan is also
similar to other sauropods in having an sacral enlargement above the hip which some older
sources misleadingly referred to as a "second brain", but glycogen bodies are a more possible
explanation. Nostril placement
The placement of Giraffatitan nostrils has been the source of much debate with Witmer
describing in Science the hypothesized position of the fleshy nostrils in Giraffatitan in
as many as five possible locations. Comparing the nares of dinosaurs with those of with
modern animals, he found that all species have their external nostril openings in the
front, and that sauropods like Giraffatitan did not have nostrils on top of their heads,
but near their snouts. There has also been the hypothesis of various
sauropods, such as Giraffatitan, possessing a trunk. The fact that there were no narrow-snouted
sauropods tends to discredit such a hypothesis. Stronger evidence for the absence of a trunk
is found in the teeth wear of Giraffatitan, which shows the kind of wear that would result
from biting and tearing off of plant matter rather than purely grinding, which would be
the result of having already ripped the leaves and branches off with its trunk.
Metabolism If Giraffatitan was endothermic, it would
have taken an estimated ten years to reach full size, if it were instead poikilothermic,
then it would have required over 100 years to reach full size. 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 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. Environment and behavior
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 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. References
External links
Media related to Giraffatitan at Wikimedia Commons