A giant tortoise by any other name

Long, heated battle ends with a moniker for the Indian Ocean reptile

One of the most passionately disputed arguments over a scientific name has finally come to an end. After 200 years of ambiguity, years of fierce debate and a record number of formal comments on the proposed name, a commission has declared gigantea the one true species term for the Aldabra giant tortoises.

HELLO MY NAME IS One of the fiercest debates over scientific names has centered on the iconic giant tortoises of the Aldabra Atoll in the Indian Ocean. Officials have voted to use gigantea as part of the species’ name. nelik/Shutterstock

That species descriptor will be used as part of a two-word Latin name that puts the species into a genus with its near relatives. Meet Aldabrachelys gigantea.

“Taxonomy is a swirling, dynamic science,” says malacologist Ellinor Michel, executive secretary of the International Commission on Zoological Nomenclature, which holds the final authority in the naming of animals. Name debates, she notes, can get “fractious.”

Confusion about the tortoise name built over centuries. Biologists have used 49 Latin names for the giants of the Aldabra Atoll in the western Indian Ocean. They can weigh several hundred pounds and live for more than a century. Taxonomic rules call for rigorously determining the earliest valid name and designating a single specimen as a benchmark “type.” But the code also calls for stability.

The issue came to a head in 2009, when Ecuador-based zoologist Jack Frazier, with the Smithsonian Institution’s National Museum of Natural History, asked the commission to recognize gigantea as the valid species descriptor for the tortoise and to use the specimen he described in 2006 for the Smithsonian as the benchmark.

Frazier argued that the term gigantea is now the most commonly used Latin term for the species. At Frazier’s urging, conservationists and other nontaxonomists who use the species name chimed in.

Normally each of the 40 or so naming disputes the commission considers in a year draws a couple of commentaries in response, Michel says. The tortoise dispute inspired more than 80 responses.

But Frazier’s call for nonspecialist opinions wasn’t appropriate, protested taxonomist Roger Bour, of the National Museum of Natural History in Paris. “Should zoological nomenclature be regulated by a set of rules or by ‘polls’ open to anyone?” he asked in a commentary he sent to the commission. The tortoise case “was initiated by nontaxonomists apparently unschooled in the rules of zoological nomenclature and unwilling to abandon a name that they have become used to.”

The case against gigantea is long and intricate, and as just one of the problems, the earliest candidate for a type specimen was either lost or mislabeled for at least 90 years. The preserved animal was moved in 1808 along with other natural history specimens from the royal collection in Lisbon to Paris after Napoleon invaded Portugal. In Paris, a young physician studying natural history dubbed the recently arrived prize as a new species, Testudo gigantea.

But his account notes that the specimen had been collected in Brazil. If that origin was correct, the physician had named a South American tortoise gigantea, not the one from Aldabra. And what happened to the specimen next is contentious.

By 1915, searches of the Paris museum collection failed to turn up the original specimen, and without access to it, scientists couldn’t check its characteristics or origin. And starting in 1835,  some taxonomists had used the Latin name gigantea for tortoises from Aldabra, not Brazil.

The specimen was actually in Paris all along but labeled under a different name, Bour announced in 2006. He argued that the specimen was the one that came from Lisbon based on such clues as its measurements and the kind of fiber stuffing and painted wooden eyes the specimen sported. And it’s not an Aldabra tortoise but a South American species that now has its own Latin name. In the end, Bour concluded that applying the rules of the code would call for dussumieri instead of gigantea.

One of the commissioners, Philippe Bouchet of Paris’ National Museum of Natural History, says he told Bour, “You are technically right, but you are socially wrong.” Sometimes what best serves society is ratifying a widely used name for an iconic animal.

After allowing several years instead of the more usual one for debate, the ICZN announced March 31 that commissioners favored Frazier’s proposal for gigantea and the Smithsonian type specimen by a vote of 19 to 4 (with an additional partial approval).

The debate has greater implications than the name of one tortoise, says ICZN Commissioner Richard L. Pyle of the Bishop Museum in Honolulu. A living species, he says, is a repository of “genomic wisdom that has allowed four billion years of ancestors to persevere though glaciation events, meteor impacts, massive climate change and all manner of other tumultuous incidents.” Keeping clear names for these species, he says, is “as fundamental to information about biodiversity as IP addresses are to the Internet.”

As someone who works with the tortoises in their native land, Nancy Bunbury of the Seychelles Islands Foundation says she’s “relieved and delighted.” At last the tortoises have a name.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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