Ploughshare Tortoise (Angonoka) (Astrochelys yniphora)

The Ploughshare Tortoise (Angonoka) (Astrochelys yniphora) is a tortoise found in the Baly Bay region, northwestern Madagascar, listed Critically Endangered on the IUCN Red List.

Common name: Ploughshare Tortoise (Angonoka)
Scientific name: Astrochelys yniphora
Conservation status (IUCN Red List): Critically Endangered
Habitat: Baly Bay region, northwestern Madagascar
Edition: TT-19: The Battering Ram

One of the rarest tortoises on Earth, a Madagascar endemic whose males wield a plough-like shell spur to flip rivals in breeding-season duels.

It is Turtle Tuesday edition TT-19, “The Battering Ram”, drawn by hand and free to download.

This drawing is one of the 26 in Color the Shell, the Turtle Tuesday turtle coloring book: the same line art in black and white, with one true fact per turtle.

This is possibly the rarest tortoise on Earth, and it knows exactly what to do with the little shovel bolted to the front of its own body. See that pale spur curving up beneath the chin? That’s the ploughshare, a forward projection of the shell built for one purpose: leverage. When two males meet in the dry season, they duel by hooking those spurs under each other and heaving; whoever gets flipped onto his back loses. The winner gets the female; the loser gets a long, undignified struggle to right himself. Fewer than a few hundred remain in the wild, all around a single bay in northwestern Madagascar, and every one is so valuable to poachers that conservationists now engrave ID numbers into their shells to make them harder to sell. Admire the golden dome, respect the crowbar, and please, no autographs.

The ploughshare tortoise, known in Madagascar as the angonoka, is one of the rarest tortoises alive, with likely only a few hundred left in the wild around Baly Bay. It’s named for a curved projection of the lower shell that juts forward beneath the neck. In breeding season, males use it as a lever, sliding it under a rival and heaving him onto his back; the flipped tortoise loses the female. Its rarity has made it the most valuable tortoise in the illegal pet trade, so conservationists now engrave serial numbers into wild shells.

The Tortoise With a Built-In Crowbar

The ploughshare tortoise (Astrochelys yniphora), called the angonoka in Malagasy, is endemic to a single region of northwestern Madagascar around Baly Bay, now protected within Baly Bay National Park. Males can reach around 45 centimeters of shell length and weigh over 10 kilograms.

Its defining feature is the one that names it. The gular scute, the frontmost plate beneath the neck, extends forward and curves up into a blade-like projection resembling a ploughshare. During breeding season males fight with it: one maneuvers his projection beneath a rival’s shell and levers upward, trying to flip him onto his back. The flipped tortoise loses, and with it access to the female.

Angonoka are slow, deliberate herbivores, grazing on grasses, herbs, and bamboo leaves and shoots. They mature slowly (females may not breed until around fifteen to twenty years old) and lay small clutches, so every lost adult is a serious blow.

The IUCN lists the ploughshare tortoise as Critically Endangered, among the most endangered tortoises on the planet: the wild population is estimated at only a few hundred, confined to Baly Bay. Today its biggest threat is collectors for the pet trade, which is why conservationists guard it so closely.

Key Moments

1885: The species is formally described; its Malagasy name, angonoka, and gular projection give rise to the name ‘ploughshare tortoise’
1986: Concern over the tiny, shrinking wild population prompts international action to save the species
1998: Durrell Wildlife Conservation Trust establishes a captive-breeding centre at Ampijoroa
2013: Conservationists begin engraving unique ID codes into wild tortoise shells to deter poachers
Present day: Listed by the IUCN as Critically Endangered, with likely only a few hundred left in the wild

Fun Facts

Named for a Plough: A blade-like projection juts forward beneath the neck like a plough’s ploughshare, the source of its name
Tortoise Wrestling: Rival males hook that ploughshare under each other and heave, trying to flip their opponent to win the female
One Bay on Earth: The entire wild species lives in a single strip of scrub around Baly Bay in northwestern Madagascar
Golden Dome: A high, polished, golden-brown shell, among the most beautiful of any tortoise
Serial-Numbered Shells: Conservationists engrave ID codes into wild shells to make them harder for smugglers to sell
Takes Its Time: Females may not breed until around 15 to 20 years old

Conservation Notes

With likely only a few hundred left in the wild, confined to the scrub around Baly Bay, it’s one of the most endangered tortoises on Earth, and one of the most closely guarded.
Durrell Wildlife Conservation Trust and Malagasy partners have run a captive-breeding programme since the 1990s and now engrave ID codes into wild shells to deter smugglers.
Durrell Wildlife Conservation Trust has bred 800 ploughshare tortoises in captivity and released 105 back into the wild in Madagascar.

Mini FAQ

What actually is the ‘ploughshare’?

It’s part of the tortoise’s own shell. The gular scute curves up into a blade-like spur like the ploughshare of an old plough. Males use it as a lever in breeding-season duels, sliding it under a rival and heaving him over.

Just how rare is it?

Extremely. It’s regularly named among the most endangered tortoises on Earth, with an estimated wild population of only a few hundred, clustered around a single bay.

Why engrave numbers into their shells?

To fight poaching. The angonoka is so valuable that its unmarked shell is part of what makes it a target. Engraving an ID code into each shell makes a smuggled animal instantly identifiable.

Art by Lee Eisenbarth, CC BY 4.0: how to use this art.

Sources: IUCN Red List, Wikipedia.