In the late 18th century earth-sciences experienced a revolution. The principles of modern rock classification were introduced and sediments subdivided by the content of embedded fossils. Animals of the past apparently differed from modern ones in their abundance, diversity, shape and some organisms were completely unknown to contemporary scholars. This observations had at first an interesting implication. If these organisms are today unknown, are they surviving in remote regions of the globe and yet not discovered ?
Classic monsters similar to fossil beasts, like the sea serpents of America , were spotted and depicted in books for centuries, but European naturalists now considered such stories as "Yankee Humbug" and in 1812 eminent French zoologist Georges Cuvier (1769 - 1832) proclaimed that there was little hope to discover new species of large tetrapods.
"…we hope that nobody thinks to search them for real, it would be like searching the animals of Daniel or the beasts of the apocalypse. Let us not even search for the mythical animals of the Persians, results of an even greater imagination."
In 1796 eminent president of the American Philosophical Society and naturalist Thomas Jefferson (1743-1826) studied some fossil bones and a giant claw discovered during mining activities in a cave. March 10, 1797 he presented the preliminary results to the Philosophical Society under the title "A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia" and concluded that these remains belong to a giant felid " three times as large as the lion" which he named "Megalonyx" (the great claw).
Fig.1. Engraving of the bones and claw of Megalonyx, as published in a paper by Caspar Wistar "A description of the Bones deposited by the President, in the Museum of the Society, and represented in the annexed plates" (1799). Jefferson's Megalonyx paper, which had no illustrations of the bones, was published in the same volume. Jefferson later recognized that the bones and claw he had attributed to his large cat Megalonyx were comparable to these of another animal, described in 1796 by Cuvier as Megatherium (image in public domain).
Jefferson believed that in nature no species could go extinct, so he concludes in his report:
"In the present interior of our continent there is surely space and range enough for elephants and lions, if in that climate they could subsist; and for the mammoth and megalonyxes who may subsist there. Our entire ignorance of the immense country to the West and North-West, and of its contents, does not authorise us so say what is does not contain."
Jefferson based this conclusion not only on the bones but in part also on anecdotes of trappers (supposedly) terrorized by a large cat-like animal in the wilderness and the presumed depiction of lions in Indian rock paintings (possibly the American lion Panthera atrox ?).
However the most important argument for Jefferson was a theological one: if a species can become extinct in a perfect divine creation such a creation can't possibly be so perfect at all. Also the continuous loss of species would inevitably lead to the end of this imperfect creation.
"The movements of nature are in a never ending circle. The animal species which has once been put into a train of motion, is still probably moving in that train. For if one link in nature's chain might be lost, another and another might be lost, till this whole system of things should be evanish by piece-meal; a conclusion not warranted by the local disappearance of one or two species of animals, and opposed by the thousands and thousands of instances of the renovating power constantly exercised by nature for the reproduction of all her subjects, animal, vegetable, and mineral."
Jefferson was also politically motivated to support the existence of large, ferocious and hidden animals in the future United States of America.
Eminent France naturalist Georges-Louis Leclerc, Comte de Buffon (1707-1788) proposed a theory to explain the worldwide distribution of animal species: from environmental optimal centers species would spread all over the globe, however degenerating in areas with less favorable climate or environment - and according to Buffon the fauna of America was an perfect example of such a degenerated primordial European and African fauna.
This worldview not only offended a proud patriot like Jefferson on a personal level, but also seriously compromised the U.S. foreign policy. The U.S. needed the political and financial support of France during the Revolutionary Wars (1775-1783), Buffon was however popularizing the perception that "America is an excessively cold and humid continent where big animals cannot survive, domestic animals become scrawny, and men become stupid and lose their sexual vigor" (ROWLAND 2009).
In spring 1785 Jefferson published anonymous his "Notes on the State of Virginia", where he discuss naturalistic and also political facts of this state. In various lists he compares the mammals of the new continent to the mammals of the old continent, concluding that the body mass and diversity of American animals was far superior then depicted by Buffon. He also reaffirmed his view on the impossibility of extinction:
"The bones of the Mammoth which have been found in America, are as large as those found in the old world. It may be asked, why I insert the Mammoth, as if it still existed? I ask in return, why I should omit it, as if it did not exist?
Such is the economy of nature, that no instance can be produced of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken. To add to this, the traditionary testimony of the Indians, that this animal still exists in the northern and western parts of America, would be adding the light of a taper to that of the meridian sun. Those parts still remain in their aboriginal state, unexplored and undisturbed by us, or by others for us. He may as well exist there now, as he did formerly where we find his bones."
What a triumph would be the display of a living Mammoth or Megalonyx at the White House? So in 1803 Jefferson organized the famous Lewis and Clark expedition; apart political important tasks, like the geographical exploration of Louisiana and the search for a navigable passage to the Pacific, this expedition could also dig for fossils and eventually search for the supposed unknown large tetrapods native to North America. Unfortunately such beasts were never caught alive…
ROWLAND, S.M. (2009): Thomas Jefferson, extinction, and the evolving view of Earth history in the late eighteenth and early nineteenth centuries. In ROSENBERG, G.D., ed., The Revolution in Geology from the Renaissance to the Enlightenment: Geological Society of America Memoir 203: 225-246