The long-necked, long-tailed Brachiosaurus wasn't the biggest sauropod ever to walk the earth, but it still ranks among the most popular. Here are 10 facts you may or may not have known about this gigantic, but gentle, plant-eater. (See a gallery of Brachiosaurus pictures.)
1. Paleontologists have identified only one complete Brachiosaurus skull.
One of the odd things about sauropods like Brachiosaurus is that their skulls were only loosely attached to the rest of their skeletons--and thus were easily detached after their deaths. It was only in 1998 that experts finally identified a skull discovered by the 19th-century paleontologist Othniel C. Marsh as definitively belonging to Brachiosaurus, rather than Apatosaurus. (Read more about the discovery of Brachiosaurus.)
2. Giraffatitan may or may not have been a species of Brachiosaurus.
The picturesquely named Giraffatitan ("giant giraffe") was native to northern Africa rather than North America, but in all other respects it was a dead ringer for Brachiosaurus. Even today, paleontologists are unsure whether Giraffatitan merits its own genus, or was a species of Brachiosaurus named Brachiosaurus brancai. (The exact same situation holds, by the way, with Seismosaurus and another famous sauropod, Diplodocus.)
3. Paleontologists once thought Brachiosaurus spent most of its time underwater.
A century ago, naturalists speculated that Brachiosaurus could only have supported its 30-ton weight by walking along lake bottoms and thrusting its head out of the surface, like a snorkel. Later, though, this theory was discredited when a detailed analysis showed that the high water pressure would quickly have suffocated the giant beast--thought that hasn't kept some people from claiming the Loch Ness Monster is a 150-million-year-old sauropod!
4. Brachiosaurus may have been a "homeotherm."
How did Brachiosaurus regulate its body temperature? Some experts speculate that sauropods took a long time to warm up in the sun, and an equally long time to dissipate this built-up heat at night--resulting in a steady state of "homeothermy." This theory is consistent with sauropods having a cold-blooded (i.e, reptilian) metabolism, but not a warm-blooded (i.e., mammalian) one.
5. The life span of the average Brachiosaurus was about 100 years.
As a general rule, the bigger and slower an animal is, the longer is its life span. Brachiosaurus' size, combined with its presumed cold-blooded metabolism, means that adults of this genus may well have reached the century mark--especially since a full-grown Brachiosaurus would have been virtually immune from predation once it aged out of its perilous childhood and teenage years.
6. Brachiosaurus wasn't the biggest sauropod.
As huge as it was, Brachiosaurus was a relative lightweight compared to other sauropods and titanosaurs, including the South American Argentinosaurus and the North American Seismosaurus (which, as noted above, might actually turn out to have been a species of Diplodocus). Adult specimens of these gigantic dinosaurs may well have surpassed 100 tons in weight!
7. The name Brachiosaurus refers to this dinosaur's front limbs.
Rather disappointingly considering its long neck, long tail and enormous bulk, Brachiosaurus ("arm lizard") was named after a less impressive feature--the relatively long length of its front, compared to its hind, limbs. However, this discrepancy in arm size does shed valuable light on this dinosaur's posture, especially as pertains to its eating habits compared to other, more evenly built sauropods.
8. Brachiosaurus feasted on cycads, gingkoes and other primitive plants.
The vegetarian menu of the late Jurassic period was rather limited in extent: since many modern plants and grasses had yet to evolve, sauropods like Brachiosaurus had to content themselves with primitive ferns, cycads and gingkoes. These giant dinosaurs probably had to eat a few hundred pounds of leafy greens every day to maintain their weight, and we won't even get into the issue of their daily poop.
9. Brachiosaurus may have held its neck parallel to the ground.
In order to raise it head to its full vertical height--over 40 feet off the ground--Brachiosaurus would have needed an enormous, muscular heart, and possibly a warm-blooded metabolism as well. That's why some paleontologists believe all sauropods held their necks level to the ground, sweeping the undergrowth like giant vacuum cleaners, though not everyone agrees with this theory.
10. Adult Brachiosaurus were pretty much immune from predation.
There's little evidence that contemporary meat-eating dinosaurs like Allosaurus hunted in packs, but even if they did, it's hard to imagine them bringing down a full-grown Brachiosaurus. Once they were past a certain age--probably anywhere from five to 10 years old, depending on their metabolism--,Brachiosaurus adults had little to fear from predators, but they still had to keep an eye on smaller, more vulnerable juveniles.