Brachiosaurus - lived 150 million to 130 million years ago from
the Late Jurassic to the
Early Cretaceous Period.
Brachiosaurs were the heaviest and tallest sauropod
dinosaurs for which complete skeletons exist; larger fossil bones
belonging to other (and possibly related) sauropods have been found,
but these specimens are incomplete. Fossilized remains of brachiosaurs
are found in Africa, North America, and Europe.
Brachiosaurs were built
like huge giraffes; they had immensely long necks and relatively short
tails. Their morphology is unusual among dinosaurs in that the
forelimbs were longer than the hind limbs. These adaptations
apparently enabled them to lift their heads to about 12 metres (39
feet) above the ground in order to browse the branches of tall trees.
Brachiosaurs attained a maximum length approaching 25 metres and a
weight of nearly 80 metric tons. Their nasal bones were expanded into
a broad arch that presumably allowed them to maintain some distance
between the vegetation and the nasal openings so that they could
breathe easily while feeding. The mouth contained a few dozen
pencil-like teeth with beveled edges. Like most other dinosaurs,
brachiosaurs did not chew their food but used their jaws to collect
food, which the tongue presumably forced into the throat. Considering
their massive size, their small heads, and the relatively poor quality
of their forage, scientists have inferred that brachiosaurs must have
spent nearly all their waking hours feeding.
The huge size of
brachiosaurs led some researchers to suggest that they spent most of
their time submerged in water, which would have served to buoy up
their great weight. The location of the nasal openings—on top of the
head and above the eyes—lent additional support to this idea. However,
water pressure at the depths needed to cover these dinosaurs would
have crushed their lungs and thus made breathing difficult or
impossible. Other features of their skeleton show that brachiosaurs
were well adapted to a life spent on land browsing the high treetops.
Their skeletons were strong but not massive, so their weight could be
supported without any help from water. Their great neckbones, for
example, are so deeply excavated that they function as a lightweight
framework of struts and plates.