For many decades, Brachiosaurus (brack-ee-oh-SORE-us) was the largest dinosaur known. It has since been exceeded in sheer mass by a number of giant titanosaurs like the Argentinosaurus and it was finally surpassed in height by another brachiosaurid, the Sauroposeidon. It was, however, still the largest dinosaur known from a relatively complete skeleton.

However, even that may no longer be true, since the largest known specimens are now considered to be part of the new Giraffatitan genus. This new genus includes the famous mounted Brachiosaurus in the Humboldt Museum of Berlin, which is the tallest mounted skeleton in the world.

Brachiosaurus is estimated to weigh from 30 to 80 tonnes (35 to 90 tons), to reach 13 meters (42 feet) in height, and 25 meters (82 feet) in length. Higher estimates are usually based on the Ultrasauros, which was originally considered to be an extremely large Brachiosaurus. However, Ultrasauros is now believed to be a chimera, composed of neck bones from a Supersaurus, and a shoulder bone (scapulacoracoid) from a Brachiosaurus smaller than the largest Giraffatitan specimens.

Description and environment

Brachiosaurus was a sauropod, one of a group of four-legged, plant-eating dinosaurs with long necks and tails, and tiny brains. Unlike other families of sauropods, it had a giraffe-like build, with long forelimbs and a raised neck, which it probably used to graze in the tops of trees. It had teeth like chisels (spatulate), and nostrils on the top of its head, which may indicate it had a good sense of smell. It had a number of holes in its skull to reduce weight. The first toe on its front foot, and the first three on its hind feet had claws. They may have traveled in herds.

It used to be theorized that it used the nostrils on the top of its head like a snorkel, and spent most of its time submerged in water to help support its great mass. However, it is now believed that it was a fully terrestrial animal. Studies have shown that the water pressure would be too great for it to breathe while submerged, and its feet are too narrow, and would sink into the mud.

Berlin's brancai and Chicago's high flyer

The mounted skeleton of a B. brancai (or Giraffatitan) in the Humboldt Museum in Berlin is 4 stories tall, reaching 12 meters (39 feet) into the air, and is 23 meters (74 feet) long. It is the tallest mounted skeleton in the world, though the bones come from several different specimens.

A Brachiosaurus is also mounted in the B Concourse of United Airlines' Terminal One in O'Hare International Airport in Chicago, courtesy of the Field Museum of Chicago. It is a model, not a collection of fossils.

Classification

Brachiosaurus has three known species:

• B. alataiensis de Lapparent & Zbyszewski, 1957: Is known from back bones (vertebrae), and parts of the hip and limbs, which were recovered in Estremadura, Portugal. It lived about 150 million years ago, during the Kimmeridgian age of the late Jurassic period.
• B. altithorax Riggs, 1903: The type species is known from two partial skeletons recovered in Colorado and United States. It lived from 145 to 150 million years ago, during the Kimmeridgian to Tithonian ages.
• ?B. nougaredi de Lapparent, 1960: While it may not be a distinct species (nomen dubium?) it is known from set of fused bones over the hip (sacrum), and parts of a forelimb, which were recovered in Wargla, Algeria in Africa. It lived 100 to 110 million years ago, during the Albian to Cenomanian ages of the middle Cretaceous period.

The best specimens of Brachiosaurus were from the species B. brancai, which was found in the Tendaguru Beds of Tanzania, in Africa. In 1991, George Olshevsky placed them in a new genus, Giraffatitan because they share no derived characteristics with Brachiosaurus. Giraffatitan has withers over its shoulder, and a rounded crest over its nostrils.

• Giraffatitan brancai Janensch, 1914 (formerly B. brancai): The new type species, it is known from five partial skeletons, including at least three skulls, and some limb bones, which were recovered in Mtwara, Tanzania, in Africa. It lived from 145 to 150 million years ago, during the Kimmeridgian to Tithonian ages of the late Jurassic period.

Discovery

The first Brachiosaurus was discovered in 1900 by Elmer S. Riggs, in the Grand River Canyon of western Colorado, in the United States. He named the new species and genera in 1903 after its long front limbs — Brachiosaurus means "arm lizard", from the Greek brachion ("arm") and sauros ("lizard").

Starting in 1909, Werner Janensch found many new specimens in Tanzania, Africa, including some nearly complete skeletons, which were widely used in Brachiosaurus reconstructions. These are now considered to be Giraffatitan fossils.

External links

• Expect awe-struck travelers (http://www.fieldmuseum.org/museum_info/press/press_brachiosaurus.htm), from the Field Museum. (O'Hare airport mount)
• Paper Dinosaurs, 1824-1969 — 18. Sauropods in the American West, 1883 (http://www.lhl.lib.mo.us/events_exhib/exhibit/ex_paper_dino.shtml), from the Linda Hall Library.