01 of 11 The First Sauropod Ever Discovered Carnegie Museum of Natural History Apatosaurus—the dinosaur formerly known as Brontosaurus—was one of the first sauropods ever to be described, cementing its permanent place in the public imagination. But what made Apatosaurus so special, especially compared to two other sauropods with which it shared its North American habitat, Diplodocus and Brachiosaurus? Discover 10 fascinating Apatosaurus facts.

02 of 11 Apatosaurus Used to Be Known as Brontosaurus Universal Pictures / Handout / Getty Images In 1877, the eminent paleontologist Othniel C. Marsh bestowed the name Apatosaurus on a new breed of sauropod recently discovered in the American west--and two years later, he did the same for a second fossil specimen, which he dubbed Brontosaurus. Much later, it was determined that these two fossils belonged to the same genus—meaning that, according to the rules of paleontology, the name Apatosaurus took precedence, even though Brontosaurus had long since become more popular with the public.

03 of 11 The Name Apatosaurus Means "Deceptive Lizard" dbrskinner / Getty Images The name Apatosaurus ("deceptive lizard") wasn't inspired by the mixup between it and Brontosaurus; rather, Othniel C. Marsh was referring to the fact that this dinosaur's vertebrae resembled those of mosasaurs, the sleek, vicious marine reptiles that were the apex predators of the world's oceans during the later Cretaceous period. Sauropods and mosasaurs were both gigantic, and they were both doomed by the K/T Extinction Event, but they otherwise occupied entirely different branches of the prehistoric reptile family tree.

04 of 11 A Full-Grown Apatosaurus Could Weigh Up to 50 Tons Wikimedia Commons As horrifyingly huge as Apatosaurus must have seemed to 19th-century dinosaur enthusiasts, it was only moderately sized by sauropod standards, measuring about 75 feet from head to tail and weighing in the neighborhood of 25 to 50 tons (compared to lengths of well over 100 feet and weighs close to 100 tons for behemoths like Seismosaurus and Argentinosaurus). Still, Apatosaurus was heavier than the contemporary Diplodocus (although much shorter), and about on a par with its other fellow sauropod of late Jurassic North America, Brachiosaurus.

05 of 11 Apatosaurus Hatchlings Ran on Their Two Hind Legs Sam Noble Museum of Natural History Recently, a team of researchers in Colorado discovered the preserved footprints of a herd of Apatosaurus. The tiniest trackmarks were left by hind (but not front) feet, conjuring up the image of 5- to 10-pound Apatosaurus hatchlings skittering on their two hind legs to keep up with the thundering herd. If this was really the case, then it's likely that all sauropod babies and young juveniles, and not just those of Apatosaurus, ran bipedally, the better to elude hungry predators like the contemporary Allosaurus.

06 of 11 Apatosaurus May Have Cracked its Long Tail Like a Whip Wikimedia Commons Like most sauropods, Apatosaurus possessed an extremely long, thin tail that acted as a counterweight to its equally long neck. To judge by the lack of characteristic trackmarks (see previous slide) that would have been left in the mud by a dragging tail, paleontologists believe Apatosaurus held its long tail off the ground, and it's even possible (though far from proven) that this sauropod "whipped" its tail at high speeds to intimidate or even inflict flesh wounds on its meat-eating antagonists.

07 of 11 No One Knows How Apatosaurus Held its Neck Wikimedia Commons. Paleontologists are still debating the posture and physiology of sauropods like Apatosaurus: did this dinosaur hold its neck at its fullest possible height to eat from the high branches of trees (which would have entailed its possessing a warm-blooded metabolism, in order to have the energy to pump all those gallons of blood 30 feet into the air), or did it hold its neck parallel to the ground, like the hose of a gigantic vacuum cleaner, feasting on low-lying shrubs and bushes? The evidence is still inconclusive.

08 of 11 Apatosaurus Was Closely Related to Diplodocus JoeLena / Getty Images Apatosaurus was discovered in the same year as Diplodocus, yet another gigantic sauropod of late Jurassic North America named by Othniel C. Marsh. These two dinosaurs were closely related, but Apatosaurus was more heavily built, with stockier legs and differently shaped vertebrae. Oddly enough, despite the fact that it was named first, Apatosaurus is today classified as a "diplodocoid" sauropod (the other major category are the "brachiosaurid" sauropods, named after the contemporary Brachiosaurus and characterized, among other things, by their longer front than hind legs).

09 of 11 Scientists Once Believed Apatosaurus Lived Underwater Charles R. Knight The long neck of Apatosaurus, combined with its unprecedented (at the time it was discovered) weight, flummoxed 19th-century naturalists. As was the case with Diplodocus and Brachiosaurus, early paleontologists tentatively proposed that Apatosaurus spent most of its time underwater, holding its neck out of the surface like a gigantic snorkel (and perhaps looking a bit like the Loch Ness Monster). It's still possible, though, that Apatosaurus mated in the water, the natural buoyancy of which would have kept males from crushing the females!

10 of 11 Apatosaurus Was the First-Ever Cartoon Dinosaur Winsor McCay / Wikimedia Commons / Public Domain In 1914, Winsor McCay—best known for his comic strip Little Nemo in Slumberland—premiered Gertie the Dinosaur, a short animated film featuring a realistically hand-drawn Brontosaurus. (Early animation entailed arduously painting individual "cels" by hand; computer animation didn't become widespread until the late 20th century.) Since then, Apatosaurus (usually referred to by its more popular name) has been featured in countless TV shows and Hollywood movies, with the odd exception of the Jurassic Park franchise and its marked preference for Brachiosaurus.