Today is Thomas Jefferson's birthday. So what would he have wanted? Probably some mastodon bones — it's one of the things he sent Lewis and Clark to find.

Jefferson carried out a lot of eccentric scientific experiments at his home in Monticello. But mastodons were one of his more unusual interests: he believed there were still mastodons roaming the unexplored West in North America, and he desperately wanted to find them.

His passion included covering the White House floor with mastodon bones, like a kid spreading out Halloween candy. And his interest in mastodons also helped form the basis for modern paleontology.

Why Jefferson believed mastodons roamed the American West

Stanley Hedeen tells the story of Jefferson's mastodon obsession in Big Bone Lick, a book about the wild early days of American paleontology. Jefferson was one of many founding fathers interested in all the bizarre fossils being discovered across North America (particularly the large supply found at Big Bone Lick in Kentucky). In 1780, for example, George Washington was intrigued by early mastodon remains found in Claverack, New York.

Patriotism was one of the big reasons the founding fathers cared so much about the fossils they were uncovering. Influential Europeans like Georges-Louis Leclerc, Comte de Buffon argued that species found in the New World were inferior to the ones found in Europe.

"the movements of nature are in a never-ending circle"

But there was also a simpler reason for the obsession. At the time, extinction wasn't an accepted idea. Many early Americans believed that the fossils they found belonged to animals that were still alive, roaming the American landscape somewhere.

In the late 18th century, the idea of extinction was only just beginning to be popularized by some thinkers (including Georges Cuvier). But Jefferson wasn't among the believers. In a pre-Darwinian age, extinction was a violation of religious ideals (God would not let animals go extinct) and secular ideals (the balance of nature could never be so significantly upset). For Jefferson in particular, extinction was just an unusual theory: "In fine, the bones exist," he wrote. "Therefore the animal has existed. The movements of nature are in a never-ending circle."

Jefferson asked Lewis and Clark to look for mastodons, and he sent Clark on a bone-hunting trip

That's one of the reasons he sent Meriwether Lewis and William Clark on their famous expedition.

Though the official purpose was to find new opportunities for commerce, Jefferson also had Lewis and Clark collect samples of the bones they found and search for any mysterious new animals. And in 1807, after their main trip had concluded, he sent Clark on a special mission to Big Bone Lick in Kentucky to collect fossil specimens.

Clark sent more than 300 bones back to the White House in 1808, and Jefferson rearranged them in the storage area that would become the White House's East Room. He then catalogued and divided the specimens, sending some of them to museums and others off to France. This wasn't a purely whimsical exercise, either: the bones helped French scientists classify the American mastodon as a different species than the European mammoth.

Jefferson's interest in bones didn't only extend to finding the mastodon, however. He also believed he was the first to identify a new creature. He thought it was a giant, ferocious lion, but it was actually something even more unusual.

Jefferson thought he found a lion. It turned out to be a giant ground sloth.

Jefferson's proudest discovery was the Megalonyx jeffersonii, which continues to bear his name. In 1797, Jefferson obtained the bones after they were uncovered from a cave. After examining them, he named the creature "megalonyx," which is Greek for "great claw." He imagined a lion-like creature that matched American ambitions: fierce, gigantic, and untamable.

It was actually a giant ground sloth that was about nine feet long, ate upright on its hind feet, and appeared in the United States, Canada, and Mexico. It lived 150,000 to 10,000 years ago.

Though Jefferson wanted to use the Megalonyx to disprove extinction — he hoped Lewis and Clark would find the animal out West — it nonetheless became an important discovery. By 1799, Megalonyx had been identified as a ground sloth, and in 1822, it got the former president's name.

Around the same time, Jefferson's view of the world changed. By 1823, he wrote to John Adams that he believed extinction was a possibility, and that animals could become extinct if they were replaced by new forms. Even if he was wrong about extinction, Jefferson's discoveries retain their importance. That, in a way, might be the best birthday present Jefferson could hope for.

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