Arnold's giant tortoise
The slightly saddle-backed carapace (to 87.5 cm) is elongate and low, highest anterior to the center and broader posteriorly than anteriorly, with a smooth to only slightly serrate posterior rim. A large cervical scute is present, but no cervical indentation. All vertebrals are wider than long, vertebral 3 is shorter than 2; vertebrals 2-4 and about the same height, but vertebrals 1 and 5 slope gently downward. The 2nd and 4th vertebrals are the longest. The 1st pleural scute is longer than the 2nd, and a depression is present along the seam separating pleurals 1 and 2. Usually 11 marginals lie on each side of the carapace, and the supracaudal (divided in some individuals) is downturned between the posterior marginals. The lateral marginals are flared over the hindlegs. The carapace is grayish-brown to black. The plastron is rather short (61-89% of carapace length), and lacks a posterior notch. Its narrow forelobe tapers anteriorly, and is longer but much narrower than the hindlobe. The plastral formula (based on the drawing in Bour, 1982a) is: abd > hum > fem > pect >< gul > anal. The gulars do not project beyond the carapacial rim. The bridge is moderate (45-65% of carapace length), and bears a single small axillary and a larger inguinal. The bridge and plastron are the same color as the carapace. The head is more blunt than in the Aldabra tortoise with a nonprojecting snout and an upper jaw that may be slightly hooked. Nostril shape and head scalation are similar to that of the Aldabra tortoise. Head, neck, limbs and tail are grayish. The anterior surface of the forelimbs is covered with large, nonoverlapping scales. No conical tubercles are present on the thighs.
The male is larger than the female and has a tail that bears a well-developed terminal scale, which is absent in the female.
Distribution and Habitat
Eighteen living individuals of this tortoise, originally described from fossil material by Bour (1982a), have now been found living in captivity in the Seychelles. Their origin is not known.
A female was observed digging a nest for over 5 hours before starting to oviposit. In total 12 eggs were laid over half an hour; the eggs had a mean diameter of 5 cm and weighed 80 g (Gerlach, 1999).
Observation of feeding behavior in captive G. arnoldi indicates that this saddle-backed species prefers browsing over grazing (Gerlach, in press). Several morphological features support these observations: a high shell aperture; the use of the triceps brachii and latissimus dorsi muscles to extend the forelimb and raise the front of the shell; and a specialized skull anatomy and musculature that enables it to feed on large, thick leaves (Gerlach, in press).
IUCN Red List Status (1996)
Not included in Baillie and Groombridge (1996); the 1997 Seychelles Red Data Book (Gerlach, 1997a) considers this species Extinct in the Wild.