[1][2] Aldabrachelys grandidieri was a giant tortoise, one of the largest in the world, measuring about 125 cm (49 in) in carapace length.

It was originally one of the six endemic tortoise species of Madagascar (two large Aldabrachelys; two medium Astrochelys; two small Pyxis).

It is distinguished from all other Aldabrachelys by a massive, flattened or depressed carapace, bulging sides of the carapace, short gulars, top of the nasal aperture is higher than the top of orbits, diverging quadrates, broad postorbitals, and a very large processus vomerinus dorsalis.

Unlike its more common sister species, the abrupt giant tortoise (Aldabrachelys abrupta (also extinct)), the massive grandidieri did not seem to have succeeded in coexisting with humans for any length of time.

species endemic to Madagascar; in an experiment, extant Aldabra giant tortoises (Aldabrachelys gigantea) readily consumed fruit of Adansonia rubrostipa.