Jefferson's Megalonyx

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In 1797, at a meeting of the American Philosophical Society in Philadelphia, Thomas Jefferson commented on a remarkable set of bones that had been sent to him recently. A peculiarly large claw and long, slender limb bones had been dug from the floor of a cave in West Virginia (that is, in the western part of Jefferson's state of Virginia as he knew it then). The notable physician, Caspar Wistar, studied the bones and, in 1799, published his report along with Jefferson's original comments. The bones were an instant sensation, attracting the attention of naturalists in America and overseas. When Baron Cuvier, the French master naturalist, learned of them he was eager to include notice and illustrations of them in his publications--a notable achievement for a uniquely American animal.

Megalonyx jeffersonii – The Evidence

Megalonyx Toe Bones
Toe bones

These fossils were found in a cave in West Virginia. Thomas Jefferson first believed them to be from a kind of lion, which he thought might still survive in the distant wilds of western America. Actually, they belonged to a species of giant ground sloth that had lived during the most recent glacial period in eastern North America.

Other cave deposits in the same region of Virginia, West Virginia, and Kentucky had yielded numerous bones of animals that no longer were seen anywhere. Their discovery was not due to the activities of cave explorers but was the work of cave miners, who often recovered fossil bones while digging saltpeter from the floors of the caves.1 Fortuitously, visitors to the cave saw these bones and thought them peculiar enough to collect, sending them to Thomas Jefferson. One can only imagine the fate of many more bones tossed away or lost to the curious and the careless. The cave faunas are well known and well studied now. They represent animal communities that lived mostly during Pleistocene time, which includes the last great Ice Age.

When Jefferson first presented the bones to the American Philosophical Society, he likened the peculiar animal to a lion, tiger, and panther--but enigmatically they were far larger than any of those familiar living animals. It raised the question, where is this animal today? And more importantly, what was, or is, this creature?

The bones from western Virginia were first mentioned when Jefferson wrote to David Rittenhouse of Philadelphia on 3 July 1796, a letter which was read by Benjamin Smith Barton to a meeting of the American Philosophical Society on 19 August 1796. The bones were from independent collections made by John Stewart of Greenbriar County (West Virginia) and "a Mr. Hopkins of New-York." Jefferson reported that they had found the bones buried three feet deep in a cave on the property of Frederic Cromer:

Some makers of saltpetre, in digging up the floor of one of those caves beyond the blue ridge, with which you know the limestone country abounds, found some of the bones of an animal of the family of the lion, tyger, panther &c. but as preeminent over the lion in size as the Mammoth [mastodon] is over the elephant.2

What made the animal so distinct from anything then known was, first, its long limb bones and the presence of a vicious claw; and second, they were far larger than any bones then known from comparable, living animals--lions, tigers, and panthers, for example. From the characteristic claw Jefferson gave the animal a name: "It's [sic] bulk entitles it to give to our animal the name of the Great-claw, or Megalonyx." The proposal had no formal standing in scientific nomenclature, since it was in an unpublished letter.

Jefferson subsequently introduced the animal formally, however, in a scientific paper read to a meeting of the American Philosophical Society on 10 March 1797. The Society's minutes record that after this meeting "two resolutions were made, one to send the memoir to the publications committee and to engage an artist to illustrate the bones, the second to have "Mr Peale...cause those Bones to be put into the best order, for the Society's use." In the meantime, Caspar Wistar carefully studied them, and compared them to the bones of similar kinds of animals; his illustrated results were published in 1799 along with the text of Jefferson's original presentation of 1797.3

The creature was not a "tiger" or a "lion" after all. Wistar and other researchers soon observed that the animal was similar to Megatherium americanum ("American large beast"), an animal whose bones had recently been scientifically described by Cuvier based on bones from Paraguay that had been sent to the museum in Madrid, Spain.4 Jefferson's fossil was that of a giant ground sloth, which Cuvier had first studiously compared to numerous other similar skeletons, including those of sloths, tatoos, pangolins, and anteaters. Neither Megatherium nor Megalonyx was like anything yet noticed--alive or dead–in the Old World. Today we understand these animals to be the vestiges of an Ice Age fauna that populated the Americas before and during the latest period of great continental glaciers. But at the turn to the 19th century there was reason to expect that the animals might yet be found alive, as we shall see.

For a quarter of a century, Megalonyx was a name by itself. Even though it had been formally published, it was nevertheless unofficial, since it had no "specific epithet," or species name, to go with it. In 1822 the creature was renamed named by the French zoologist Anselme Ga"tan Desmarest (1784-1838), who honored Thomas Jefferson. He called it "MégathËre de Jefferson, megatherium Jeffersonii"--"Jefferson's megatherium." In being the first to affix a species name (jeffersonii) to the fossilized animal from West Virginia, Desmarest had finally provided a "full name" for the creature.5

But Desmarest's effort didn't settle the matter. In scientific naming, despite good intentions, errors can creep in, and when discovered, the mistakes must be corrected. Even though Desmarest was the first to name Jefferson's fossil, and even though he referred the animal to the genus Megatherium, his action also connected "jeffersonii" to Megalonyx, the name that Thomas Jefferson had formally presented in print in 1799. With any taxonomic name, chronological priority arbitrates the use of names if an animal (or plant) is unknowingly given more than one name. It may seem that Desmarest's "Megatherium jeffersonii" was the first full name and thus that is what the animal should be called. But biologically, Megalonyx is a kind of animal that is distinct from Megatherium; they are not synonyms. Desmarest was in error in his anatomical pronouncement that Jefferson's creature was a member of the genus Megatherium. So, for this reason the creature first known from the West Virginia cave is still called, correctly, Megalonyx jeffersonii–"Jefferson's giant claw."

Today, Thomas Jefferson's Megalonyx bones reside in the collections of the Academy of Natural Sciences of Philadelphia, sent there by the American Philosophical Society in the mid-1800s when the Society removed itself from the business of maintaining collections of natural history specimens. There are nine bones of the manus (the "hand," including its claw), and a radius and an ulna (long bones of the foreleg). The years have taken their toll somewhat. The ulna is broken near the middle of the shaft now, damage that is not shown in Caspar Wistar's illustration in 1799. The specimens are lighter in color, too, where people tend to grasp them, an unwitting testimonial to their popularity. Meriwether Lewis probably held them, too. Both of the long bones have writing on them, mostly illegible now, but from the lengths of the words and the kinds of pen strokes still visible, they indicate that the bones are the radius and ulna of Megalonyx jeffersonii–as if someone had thought that the identity of such historic bones might someday be forgotten!


1. Saltpeter is potassium nitrate (niter) and sodium nitrate (soda niter), which are naturally occurring products of the bacterial decomposition of vegetation and excrement in warm climates. It is used in manufacturing gunpowder, glass, and acids. It is also used as an additive in meat curing and pharmaceutical preparations, among other long-established uses. It once was considered an essential ingredient in magical potions.

2. Thomas Jefferson to David Rittenhouse, 3 July 1796, American Philosophical Society.

3. Thomas Jefferson, "A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia," Transactions of the American Philosophical Society, vol. 4 (1799), pp. 246-260. Caspar Wistar, "A Description of the Bones Deposited, by the President, in the Museum of the Society, and Represented in the Annexed Plates, Transactions, pp. 526-531, plates. (Thomas Jefferson was also President of the American Philosophical Society at the time.) Charles Willson Peale, the eminent artist, museum curator, and patriot was a member of the American Philosophical Society. He was charged with properly preserving and storing the bones of Megalonyx.

4. Georges Cuvier, "Notice sur le Squelette d'une TrËs-grande EspËce du QuadrupËde Inconnue Jusqu'a Présent, Trouvé au Paraguay, et Déposé au Cabinet d'Histoire naturelle de Madrid," Magasin Encyclopedique, vol. 1, no. 3 ("L'an quatriËme", 1796), pp. 303-310, plates; and English translation in abridgement, "Notice Concerning the Skeleton of a Very Large Species of Quadruped, Hitherto Unknown, Found at Paraguay, and Deposited in the Cabinet of Natural History at Madrid," Monthly Magazine (London), vol. 2, no. 8 (September 1796), pp. 637-638, plate.

5. A. G. Desmarest, "Mammalogie ou Description des EspËces de MammifËres. Seconde Partie," Mme Veuve Agasse (Paris, 1822).