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Jefferson’s Old Bones

Did the so-called father of American vertebrate paleontology believe in fossils?

Keith Thomson

Scientist and Lawyer

It is inappropriate to judge Jefferson, as Simpson did, by our own standards, and many a great scientist turns out to have been (in our estimation) wrong some of the time. Nonetheless, as is often the case with Jefferson, a puzzle remains. Did he deliberately avoid using the word “fossil” in reference to the mastodon and Megalonyx? If so, did he do it as a lawyer and for strategic, rhetorical reasons, or as a scientist, or as both? From our modern point of view, the dilemma Jefferson faced is easy to outline. There was no consensus on how petrifaction occurred, how long it took, and indeed, how sea shells came to be found high up in mountains, how mountains were formed or how old the Earth was. And there was no unanimity about whether extinction was a real phenomenon. In each of these questions, some contemporary philosophers were edging toward modern solutions, whereas others were exploring versions of a flood theory or hypothesizing about impacts with comets. Jefferson, aware of the trends, evidently found his ideas and information to be in conflict.

From a religious point of view, Jefferson did not want to accept extinction, but there was also enough anecdotal evidence to suggest that Megalonyx, at least, might still be alive in the west to support him in that conclusion. He was unsure to what extent his “bones” were petrified. It seems that his solution was to be extremely careful in his word usage. As a master of language and of precise use of rhetoric, Jefferson seems to have kept his options open by simply avoiding use of the word fossil and by sticking to terms whose meaning was precise and unequivocal. By referring to the fossils of mastodon and Megalonyx (which in any case, we now know were only 8,000 to 12,000 years old) simply as bones, tusks and teeth, he wrote with strict accuracy and preserved his philosophical position.

With his perceptive analysis of the mastodon and other elephants in Notes on the State of Virginia and his account of Megalonyx, Jefferson made significant contributions to scientific knowledge. He certainly encouraged the discovery and study of fossils by people such as Charles Willson Peale and physician Caspar Wistar (whose own analysis of Megalonyx, published alongside Jefferson’s, was a masterpiece of forensic anatomy). Jefferson was misled by his hopes that the mastodon and Megalonyx were mighty ferocious carnivores that would symbolize American vigor (and contradict European claims of the inferiority of American wildlife), but he was in many ways the progenitor of our modern fascination with another set of monsters from the west—dinosaurs. In these respects, he can fairly be considered a founder of American vertebrate paleontology. But the irony remains that he helped found a discipline without having accepted two of its fundamental premises: fossils and extinction.


  • Simpson, George Gaylord. 1942. The beginnings of vertebrate paleontology in North America. Proceedings of the American Philosophical Society 86:153–188.

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