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Your Village: A history of Rusty the Giant Sloth


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Rusty the Giant Sloth, UI Museum of Natural History. — Zak Neumann/Little Village

Why isn’t Rusty the Giant Sloth the official state fossil? —ME, Iowa City, via the Your Village feature on LV’s homepage

The short answer is Iowa doesn’t have an official state fossil. But if it did, a lot of people in Iowa City and University of Iowa alumni elsewhere would probably be in favor of Rusty having that honor. Since the giant ground sloth—Megalonyx jeffersonii, if you want to be scientific—went on display at the University of Iowa’s Museum of Natural History in 1985, it’s become a beloved local figure and the museum’s mascot.

Of course, being extinct helps make Rusty more charming than alarming. Megalonyx means “great claw,” a feature you can see when you look at Rusty (who is a pure product of the ’80s, no original Pleistocene parts). The giant, red-headed sloth would probably seem more menacing if it was still alive and you suddenly encountered one: 8-to-10 feet long and weighing more than a ton, in addition to being equipped with great claws.

Megalonyx was one of two giant ground slots that used to roam (or lumber around) the Midwest during the Pleistocene epoch. The remains of the equally extinct Paramylodon harlani have also been discovered in Iowa. Both were roughly the same size, and both were herbivores. But Rusty’s side of the family clearly got the more impressive name.

Paramylodon means “like the mylodon,” mylodon being a name for a type of giant ground sloth that lived in South America. It means “molar tooth,” which was the first part of the animal identified. Harlani refers to Richard Harlan, a distinguished but largely forgotten American scientist of the early 19th century and the author of Fauna Americana; being a Description of the Mammiferous Animals inhabiting North America, published in 1825. Ten years later, Harlan was the first to describe the sloth that bears his name in a scientific journal, after a lower jaw of the animal was unearthed in Pennsylvania.

Harlani is a respectable name but it lacks the marquee value of jeffersonii, which is a Latinized version of Jefferson. As in Thomas Jefferson. Yes, that Thomas Jefferson.

Jefferson is sometimes given credit for first discovering the bones of the Megalonyx, and more often credited with being the first person to describe the species in a scientific paper. The first claim is wrong, and the second one isn’t exactly right.

In 1796, Jefferson, already well-known as an enthusiastic amateur scientist, was sent some bones of the then-unknown Megalonyx that had been dug up in a cave near Greenbriar, West Virginia (which was then still part of Virginia). Those bones included claws.

The following year, Jefferson — now vice president of the United States — brought the bones to Philadelphia, where he gave a presentation to the American Philosophical Society in Philadelphia on the “Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia.” That presentation is traditionally considered the beginning of vertebrate paleontology in the United States.

But Jefferson didn’t have Rusty in mind when he came up with the name Megalonyx. He imagined the bones belonged to some sort of mega-lion. In a letter, Jefferson said he felt sure “the bones were those of a great cat, some three times the size of a lion.” In his 1797 presentation, Jefferson compared the bones to various kinds of lions, but didn’t commit to the mega-lion theory.

Going back to his vice-presidential duties, Jefferson left the bones with the society for other members to study. When Dr. Caspar Wistar examined them, he realized right away they couldn’t belong to any sort of cat, and saw the resemblance to the remains of a mylodon that had recently been discovered in South America.

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Wistar wrote to Jefferson explaining why Megalonyx had to be sloth. In 1799, when the American Philosophical Society published a version of Jefferson’s presentation, it published an accompanying article by Wistar identifying Megalonyx as a giant ground sloth.

It was Wistar who suggested in 1824 that jeffersonii be added to Megalonyx’s name. Megalonyx jeffersonii became the official name of Rusty’s family the next year, when Richard Harlan used it in a scientific paper.

If the Megalonyx did become the official state fossil, it would be the second one named for Jefferson. The state fossil of Virginia is the Chesapecten jeffersonius, a kind of an extinct scallop. Jefferson had nothing to do with the mollusk, but its discoverer admired him.

Rusty the Sloth, an exhibit at the UI Museum of Natural History. — Tom Jorgensen/University of Iowa

Despite Rusty’s popularity, he wouldn’t be the only candidate for Iowa’s state fossil. In 2018, Iowa City’s own Sen. Joe Bolkcom introduced a bill naming the crinoid as the state fossil. The crinoid is a type of marine invertebrate, also known as a sea lily and is a distant cousin of the sea cucumber.

Crinoid fossils are so common around Burlington, the city is known as “The Crinoid Capital of the World,” among people who know about the sea creatures and have heard of Burlington. Unlike the Megalonyx, crinoids still exist, just nowhere near Iowa, since there’s no longer an ocean here.

Bolkcom told the Des Moines Register in 2018 he introduced the bill at the request of several geologists who felt the 500 million year-old creatures deserved the credit.

The bill never got a committee hearing and quietly died.

This article was originally published in Little Village issue 285.


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