Madagascar Radiated Tortoise Astochelys radiata Shaw, 1802

Of the five species of tortoises found in Madagascar today, Astrochelys radiata is the best known. It is considered one of the most beautiful and admired tortoise species in the world because of its striking ray markings. It is the closest relative of the Malagasy Ploughshare Tortoise (Astrochelys yiniphora), which now only occurs in a small range in northwestern Madagascar. Both species are critically endangered, but the Radiated Tortoise is much less endangered than the Ploughshare tortoise because of its wider geographic range.

The Radiated Tortoise as well as its sister species were assigned to the genus Geochelone for a long time. This was questioned for a long period of time and in 2007 these two species were reassigned to the genus Astrochelys Gray, 1873, which is endemic to Madagascar and includes only these two species.

By native tribes Astrochelys radiata is also called Sokake, Kotroky or Tsakafy in Malagasy.

The species name "radiata" means "radiating" in Latin and refers to the significant, radiating carapace pattern of this species. The individual ray pattern is not only typical of the species, but also a unique and distinctive identifying feature of each specimen. The pattern of lines on each rayed turtle shell, like a fingerprint, exists only once in the world.

Description

Size and weight

With a shell length of up to 40 centimeters and a weight of 15 kilograms, the Radiated Tortoise is one of the relatively large tortoises. Due to constant, good conditions, animals in captivity are likely to gain size and weight faster and reach maximum body mass sooner than specimens in the wild. Adult males are on average 7% larger than adult females (O'Brien, 2002).

Measurements of adult Radiated Tortoise populations in the wild yielded the following data: The average carapace length of adult males is 33.4 cm (range = 28.5-39.5 cm), and the average weight of adult males is 6.7 kg (range = 4.5-10.5 kg). The average carapace length of adult females is 30.5 cm (range = 24.2-35.5 cm), average weight of adult females is 5.5 kg (range = 3.1-10.2 kg) (Pedrono, 2008).
Description

A distinctive feature of this species is the extremely high-arched, spherical and smooth dorsal carapace with the eponymous yellowish lines radiating outward on each carapace segment on a dark background. In most rayed turtles, the base color of the carapace is lacquer black with characteristic yellow stripes emanating from a light center. The reverse color variation with a light yellow background and black radial stripes is less common. The ray pattern, which is individual for each specimen, continues on the dorsal carapace as well as on the ventral carapace. The basic color of the plastron is yellow and shows a pattern with black areas and lines.

In young specimens, the ray markings are usually particularly colorful and distinct. With age, the characteristic pattern increasingly fades and due to wear (rubbing against stones and bushes) the concentric growth rings of the carapace are usually no longer recognizable. Very old specimens may therefore be completely washed out yellow or black. A distinction is made between dark and light individuals based on the amount of yellow present. Particularly conspicuous and popular are ray turtles, which have a clear, uniform, yellow ray markings pronounced on all shields. These specimens are also referred to as "High Yellow". Animals that are completely devoid of markings and are completely black are rare. Although the yellow and black line pattern may appear conspicuous at first glance, the outlines of a resting ray tortoise completely dissolve in a dry grass or scrub environment. Hatchlings of Astrochelys radiata still possess an inconspicuous baby camouflage pattern in their first year of life. This makes them particularly well protected from predators on sandy, stony soils and in dry foliage. The characteristic ray pattern becomes visible only with the appearance of the first growth rings, after about 1 ½ years.

The top of the head is ash colored and may have several light spots, the throat and neck are cream to yellow. The very stout legs and tail also have a yellow coloration. The horn scales of the forelegs are round and flat. The claws are conical and rather blunt. Unlike its sister species, the Malagasy Ploughshare Tortoise, it does not have a prominent extension of the gular shield at the anterior end of the ventral carapace. The posterior marginal shields are somewhat curved up and serrated, and the caudal shield is undivided and curved downward. The ventral carapace is yellow with a large black triangle on the outer edge of each of the arm, thoracic, ventral, and thigh shields. The throat shields are mostly featureless. The anal shields and sometimes the ventral shields have black ray markings. A nuchal shield is present, the supracaudal shield is undivided, and there are 11 marginal shields on each side of the carapace.
Age

Radiated Tortoises can reach an age of over 180 years in captivity due to good, constant keeping conditions. Historically documented is the age of the ray turtle named Tu'i Malila (* before 1778; ? 19. May 1965), which according to tradition was given to the royal family of Tonga by Captain James Cook. The gift by Cook is said to have been made in 1777 during his third voyage to the South Seas. During a visit of Queen Elizabeth II and Prince Philip in 1953, Queen Salote presented the turtle to them as the "oldest inhabitant of their kingdom". The animal lived with the royal family until its natural death on May 19, 1965. According to this information, Tu'i Malila would have been at least 188 years old. She was thus considered the oldest of all turtles and at the same time of all terrestrial vertebrates, until in 2006 the age of the Indian giant tortoise Adwaita became known, which with presumably 255 years reached a much higher age.