Answer: Mammoths

There is an oft repeated bit of lore that hinges on the idea that Lewis and Clark expected to find dinosaurs when they headed West across North America. It’s one of those bits of school yard trivia that, if you were to press the sharer with the simple question of “Why on Earth would they expect to find dinosaurs?” you’d be lucky to receive even an off-the-cuff answer.

Like many bits of strange folklore that circulate about, however, there’s a tiny kernel of truth buried deep within the strange statement that the expedition expected a dinosaur encounter. While dinosaur skeletons like the kind we’re used to seeing in museums had yet to be discovered (Lewis and Clark had no notion, for example, that anything like a Tyrannosaurus Rex had ever walked the Earth), just before their expedition there were fossilized bones of mammoths found in North America and Western Europe.

Now, to a modern reader, the discovery of fossil bones simply indicates evidence of a creature that lived long ago. To Lewis and Clark, as well as their contemporaries, those bones indicated that somewhere on Earth there were giant elephant-like creatures roaming around. They and their contemporaries had no conception of extinction, nor was it believed that God would ever allow one of his creations to cease to exist. That, coupled with the evidence that North America clearly had larger mammals than Europe (such as moose), it seemed entirely plausible to people at the time that somewhere beyond the reaches of North America that had already been domesticated there could be huge herds of mammoths roaming about.

Although they never encountered any live mammoths, the expedition did stop by Big Bone Lick in Kentucky, a fossil-rich region, and Lewis sent back samples to Thomas Jefferson as well as a very long letter describing their discoveries there, the potential of meeting a living relative of the bones he was sending back, and his fascination with the site. The letter would prove to be the lengthiest surviving piece of correspondence produced by Lewis.