A museum specimen of the turtle once called Pelusios seychellensis.
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Modified from Stuckas et al., 2013.
A museum specimen of the turtle once called Pelusios seychellensis.

The Turtle That Wasn’t There

Last month I attended a TEDx symposium on the controversial prospect of “de-extinction.” All day long, I heard researchers of various stripes give their expert opinions on whether we can – and should – reinvent extinct species to add a new dimension to conservation. But there is another way to de-extinctify a species. Researchers Heiko Stuckas, Richard Gemel, and Uwe Fritz have just removed a turtle from the ever-growing list of extinct species by demonstrating that the reptile never existed in the first place.

Sometime between 1901 and 1906, the Natural History Museum in Vienna, Austria acquired a trio of turtle specimens from the Zoological Museum Hamburg. According to the labels, the reptiles had been collected by the German naturalist August Brauer a decade before, when Brauer sampled critters from the island of Mahé – part of the Seychelles island chain, situated nearly halfway between India and Madagascar. Strangely, though, the turtles closely resembled a species found hundreds of miles away on mainland Africa.

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A map showing the range of Pelusios castaneus (blue) and the supposed island species P. seychellensis (red). From Stuckas et al., 2013.

When the Viennese zoologist Friedrich Siebenrock had a look at the preserved reptiles in 1906, he was struck by how closely Brauer’s turtles resembled a turtle now known as Pelusios castaneus – a turtle found over a wide swath of western Africa. If the distance between the mainland and island turtles were not so great, Siebenrock commented in his description of the Mahé turtles, he’d be tempted to call them the same species. But there was no way the little turtles could have crawled all the way across Africa, nor somehow dispersed from habitat to habitat around the edge of the continent. The distance deemed that the two had to be different species.

Not everyone agreed with Siebenrock’s conclusion. For years afterward, different researchers often lumped Brauer’s turtles into the west African species or another island species on the basis of anatomy. That is, until 1983 when herpetologist R. Bour proposed that Brauer’s old specimens truly did represent a distinct species. Bour called the turtles Pelusios seychellensis, and it seemed that Brauer had collected some of the last ones. Several searches after 1983 tried, and failed, to find the turtles. In the span of a century, it seemed, Pelusios seychellensis had gone extinct – perhaps the only time on record that humans totally exterminated a species of freshwater turtle.

But Siebenrock’s hunch about the connection between the island and mainland turtles was more right than he knew. When Stuckas, Gemel, and Fritz sampled mitochondrial DNA from the museum specimen that bears the name Pelusios seychellensis and compared those genetic clues to those of other turtles, they found that the museum specimens fell within the range of variation for west African Pelusios castaneus individuals. The unique island species never actually existed. Somehow, researchers had misidentified Brauer’s specimens. But how could west African turtles have found their way to Mahé? According to Stuckas and colleagues, they didn’t.

There’s no evidence that Brauer’s turtles hauled themselves clear across Africa. Nor is there any indication that humans brought them there at some point in the past. All this confusion might simply be the result of poor labeling and miscommunication.

Brauer took the trip during which he was supposed to have collected the turtles between May 1895 to January 1896. But he didn’t immediately give his finds to a museum. Specimens from his private collection didn’t get transferred to the Zoological Museum Hamburg until five years after the Seychelles trip, and those turtles soon went on to Vienna’s Natural History Museum. Somewhere in all that shuffling, the west African turtles might have been lumped in with the Seychelles reptiles or otherwise confused. Whatever happened, though, a prominent clue indicates that the turtles were not collected from the wild. One, and possibly two, of the turtles have a perforation through their shells identical to the sort that turtle purveyors have traditionally used to tie turtles together until they are sold for food. Wherever Brauer got the turtles from, he seems to have purchased them.

This isn’t the first time bad bookkeeping has led zoologists to erroneously erect new species. Stuckas and coauthors point out two other instances – a mislabeled American snapping turtle was confused for what was thought to be a new species from New Guinea’s Fly River, and a supposed new tortoise found in Vietnam turned out to be “an escaped pet tortoise from Madagascar.” This is why well-kept locality data and responsible curation practices are essential. We need to know when, where, and how a specimen was collected to understand what we’re studying. (Paleontologists also know this well.) And that context is not only essential for exploring the diversity of life, but also conservation. In our efforts to assist imperiled species, we need to know whether or not we’re looking at something unique and critically endangered, a wayward member of a more common species, or whatever other alternative may be the case. Understanding even such a basic facet of ecology as the identity of a species requires a great deal of attention and care.