BRACHIOSAURUS

Upon discovery in 1900, Elmer Samuel Riggs hailed Brachiosaurus altithorax as "the largest known dinosaur" and at the time he was dead right. Since then though, much larger dinosaur remains have been discovered, and heck, it may not even be the biggest member of its own family; Brachiosauridae. Problem is, brachiosaurids are pretty rare, their remains—some big, some huge—are mostly fragmentary, and each critter may have been different proportionately. On top of that, there is some dispute about which animals belong to this family and until more, and more complete, remains turn up it's all "ifs", "buts" and "maybes".

The forelimbs of Brachiosaurus were much longer than its hind limbs, but they were all surprisingly slender, and its chest was remarkably deep. These giraffe-like proportions meant its long, thick-set neck was more vertically oriented than other sauropods, so it required a shorter counter-balancing tail. But its raised neck also raised questions about blood flow and how it managed to get oxygen to its tiny head which has, itself, courted plenty of speculation down the years.

Once upon a long ago, paleontologists surmised that Brachiosaurus was a sea-dweller and its stout, dome-topped noggin with nostrils on top acted as a kind of pre-historic snorkel. This theory has since been blown out of the water as its lungs couldn't work under the pressure of total submersion, its nostrils were probably closer to the end of its snout, and its feet were too narrow to use as flippers. Funnily enough, the shorter, dome-profiled skull mentioned above actually belongs to Giraffatitan from Tendaguru—the critter once known as Brachiosaurus brancai. But that was officially severed from Brachiosaurus in 2009 by Mike Taylor, who found the two beasties differed in shape and proportion of almost every comparable body part.

Although huge, the neck and trunk of Brachiosaurus (and other saurischian dinosaurs, such as Aerosteon and Sauroposeidon) contained air sacs which were connected fore and aft to the lung, and created "air holes" by invading the vertebrae and ribs—a process known as pneumatization. This invasion would significantly reduce the overall bone density of what would appear to be a massive, lumbering oaf. But the air sacks may also have bellowed air through a rigid lung thus creating a one-way "flow-through" system, which means that Brachiosaurus and its ginormous brethren breathed in the same way as a much smaller and more familiar "dinosaur"... the modern bird!

Unlike other sauropods who were probably able to double or perhaps treble their reach by rearing up on their hind legs, this front-loaded dinosaur with a forward-positioned center of mass was ill-equipped to do so. Fortunately, long front legs and a deep chest meant its neck left its body at a much steeper angle than other sauropods, so while its powerful jaws and chisel-like teeth were ideally suited to dealing with tough, lower-lying foliage it could conceivably browse from treetops, where the most tender leaves and stems reside.