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November 1, 2021

Curators’ Casebook is our ongoing series in which we look at some of the curious cases USGS curators at the Smithsonian National Museum of Natural History deal with on a regular basis. 

In 1818, naturalist Constantine Rafinesque set out on a little trip down the Ohio River, exploring the still very young western United States. These areas were settled, but still developing, and very much new to science. In fact, science itself was fairly new and the fields of biology and taxonomy were also still developing.

Along the way, Rafinesque collected fossils, shells, fish and plants, some of which he eventually shipped to natural historians in Europe. He also visited fellow naturalists, examining their collections and herbaria, and sometimes collecting with them. In fact, in one memorable episode, fellow naturalist John James Audubon played a bit of a prank on Rafinesque.

By the end of his journey, Rafinesque also claimed to have discovered 25 new species of mammals, including a species of skunk that Rafinesque named Spilogale putorius interrupta, commonly known as the Plains Spotted Skunk.

Or did he?

Later research showed that his trip down the Ohio River Valley did not take him anywhere near the original locality of that species of skunk. Without a type specimen to verify the identity of the skunk in question, is it possible that Rafinesque was misled again?

What’s Your Type?

Identifying someone’s type might seem like the stuff of modern dating apps, but for taxonomists, it is used to establish a baseline. Enter the holotype, or “type specimen,” the individual member of a species used to create the accepted description of the species, and its type locality, a reference to the place where the type specimen was found.

Baseline types are important, because as conditions change, the species may evolve and differ from its original description. Or, more commonly, its range may differ from its original locality as its habitat is altered by things such as human encroachment, climate change, or other factors. The type is also important for understanding the characteristics of a species, particularly when there are subtle distinctions between species.

Constantine Rafinesque, a prolific naturalist. Public Domain,

A Case of Mistaken Identity?

Back to Rafinesque. His type specimen for the Plains Spotted Skunk is frustrating to taxonomists, because he does not explain where he saw the specimen or how he came across it. He does not even provide an illustration for it. Even one of the few potentially useful pieces of information he does provide—that the skunk “inhabits Louisiana”—is not helpful, because at the time Rafinesque was exploring, Louisiana did not just refer to the modern state. It was also the name of the vast territory west of the Mississippi River that the United States had purchased from France in 1803.

Further confounding taxonomists, the traditional range of the Plains Spotted Skunk is west of the Mississippi River and north along the Missouri River. Yet, Rafinesque makes it clear from his writings that he never set foot west of the Mississippi River and may not even have made it to the Mississippi River at all.

Is it possible that the type specimen was never actually a Plains Spotted Skunk but was, in fact, the Appalachian Spotted Skunk?

Unraveling the Records

USGS scientist Neal Woodman and Field Museum of Natural History scientist Adam Ferguson decided to piece together Rafinesque’s confusing meander down the Ohio River to see if they could determine the true provenance of this suspicious skunk.

After poring through the records, they were able to establish a fairly clear timeline of Rafinesque’s adventure. The farthest west he records is a town called Carmi in southeast Illinois near the Wabash River. It is possible that, after retracing his steps to Indiana, he again crossed into Illinois to visit Shawneetown along the Ohio River, but that is unclear. Regardless, he clearly never made it as far west as the mouth of the Ohio River, let alone anywhere near the Missouri River.

So where did the skunk Rafinesque described come from? Woodman and Ferguson found an important clue in the mention that Rafinesque spent a day in Middletown, Kentucky, visiting another naturalist by the name of John Bradbury. A few years earlier, Bradbury had accompanied the Astor Expedition for its first leg up the Missouri River.

While on the Astor Expedition, Bradbury records having shot a skunk and obtained the skin from it. At the time, there was only one species of skunk thought to live in North America, and Bradbury assumed this skunk was that species. When Rafinesque stopped by to visit Bradbury, it is possible that Bradbury showed Rafinesque the skunk pelt, and Rafinesque took the opportunity to jot a quick sketch of it and report it as a new species.

This made sense to Woodman and Ferguson, who realized that Rafinesque’s description and sketch are consistent with a pelt that has aged for some time in a person’s collection. The head, feet, and tail are missing, the brownish color of the fur matches the aging expected from sunlight damage, and—unlike his other sketches, which usually showed a living animal in profile—the sketch for the skunk was an oval shown from above, resembling a pelt on display.

Once Woodman and Ferguson were sure that they had identified where Rafinesque had seen the skunk, they still needed to figure out where Bradbury had originally caught it. Fortunately, the Astor Expedition took decent notes about its progress, so they were able to narrow down the official locality for the Plains Spotted Skunk to a broad expanse of Missouri River floodplain in north-central Missouri, between the modern-day towns of Brunswick and Glasgow.

Closing the Record

By identifying the source of the specimen Rafinesque used to name the species, Woodman and Ferguson were able to solve two mysteries at once: whether the Plains Spotted Skunk’s original locality was correct and whether its holotype was correctly identified. The answer is no for the original locality—instead of originating near the upper Missouri River, the skunk had come from the lower Missouri River—but yes for the holotype, which was a bona fide Plains Spotted Skunk.

Now, anyone that does research that involves the Plains Spotted Skunk, can rely on the original identified range and species, so if the skunk’s range changes due to outside factors, that can be documented. Hopefully that documentation will not require a similar hunt through archives after the next 200 years goes by.

The study by Woodman and Ferguson can be accessed here.

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