THOMAS JEFFERSON, MEGALONYX, AND THE STATUS OF PALEONTOLOGICAL THOUGHT IN AMERICA AT THE CLOSE OF THE EIGHTEENTH CENTURY

In the spring of 1796, as Thomas Jefferson was vacillating about whether or not to allow himself to be drawn once more into the political arena as a candidate for president, he received in the mail some fossil bones. As events unfolded, he did run for office, and he lost the election to John Adams. Freed (until 1801) from the burden of the American presidency, and excited by the more inviting prospect of describing and interpreting fossils, Jefferson sat down and wrote one of the most historically insightful papers in the history of American science: A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia. In this paper Jefferson described an animal that he named Megalonyx. Megalonyx is now known to be a ground sloth, but Jefferson (who had only limb and foot bones to examine) at first thought it was a giant lion.

Two aspects of Jefferson's Megalonyx memoir are especially revealing about the status of paleontological thought at the end of the eighteenth century. The first is Jefferson's discussion ¯ and rejection ¯ of the concept of extinction. Extinction was philosophically incompatible with the great-chain-of-being worldview that dominated eighteenth-century America and Europe, and there was plenty of unexplored wilderness where megalonyxes might still be living. No animal had yet been documented to be extinct. The second insightful aspect of this memoir is the way Jefferson used Megalonyx to refute Buffon's argument that New World animals were small, degenerate varieties of Old World species. These two aspects of Jefferson's megalonyx memoir capture the essence of paleontological thought in America at the close of the eighteenth century.

During the first decade of the nineteenth century the prevailing American paradigm concerning fossils and the history of life were swept away, primarily by the publications of Cuvier in France, but also by the exploration of the North American wilderness by Lewis and Clark. However, although Jefferson lived until 1826, he was never able to completely abandon his eighteenth-century worldview.