The reptile fauna of the Mascarenes was not only diverse but also occurred in huge abundance. For example, the islands probably harboured the greatest concentration of tortoises anywhere and their rapid extermination particularly epitomises the destructive capabilities of humans. The reptilian faunal origins probably lie in Australasia and Madagascar, but affinities are difficult to establish. Remarkably, an endemic subfamily of snakes occurred on Mauritius, with their nearest relatives in S. E. Asia and Australia.
The genus Cylindraspis has been proposed for the endemic Mascarene tortoises and, although they have generally been merged with Geochelone, the generic status has now been confirmed by DNA analysis. There are now known to have been five species of Mascarene giant tortoise. On Mauritius there were two sympatric species, the domed C. inepta and saddle-back species C. triserrata. Similarly on Rodrigues, a smaller, domed C. peltastes was sympatric with the large saddle-backed C. vosmaeri. On Réunion, one variable species existed, C. indica. DNA analysis has confirmed that the genus is monophyletic and initially colonised Mauritius, reaching the other islands through inter-island dispersal, firstly to Rodrigues and then to Réunion. The genus was characterised by some very distinct features, e.g. a shell often averaging only 2mm in thickness, wide open ends to the carapace, extremely reduced plastron and lack of heavy scales on the fore and hind limbs. This evolutionary trend is related to the dismantling of defense mechanisms, i.e. the energy requirments of producing heavy protective armour is thus reduced.
Giant tortoises were first reported and illustrated in the publication, Het Tvveede Boeck in 1601, based on the journal of Admiral Jacob Cornelis van Neck. Due to their ability to survive on board ship without food and water for months, tortoises were highly prized food animals. They were collected in vast numbers and loaded onto visiting ships. Oil extracted by boiling the tortoises was particularly sought after and 400-500 animals were needed to make a single barrel. In 1673, Governor Hugo on Mauritius reported the carnage and massacre of tortoises, with holes smashed into their shells to see if they contained fat . As many as fifty were slaughtered before a fat individual was found, and the bodies were left to rot. On Mauritius, legislation as early as 1639 to protect the tortoises proved ineffective, and reports of living tortoises on the mainland became scarce by the 1690s. The outlying islands, particularly the northern group, supported populations of endemic tortoises but they were hunted to extinction by c.1730.
Réunion fared no better and the tortoises, having been reported as superabundant in the 1600s, had all but disappeared by the 1730s. It is possible that a small population, undiscovered for another century due to impregnable terrain, survived until at least the 1830s.
The tortoise populations on Rodrigues, perhaps the densest anywhere, not only suffered from direct hunting, but were systematically harvested and sent to Mauritius and Réunion to replace the exhausted stocks there. This trade accelerated during the French occupation of Mauritius in 1710. Special pounds were created in Port Louis, capital of Mauritius, to husband the incoming Rodrigues animals. Meantime, slash and burn forest clearance by tortoise hunters destroyed the available habitat, and introduced pigs and cats wreaked havoc amongst the nesting sites. The intense slaughter of tortoises finally ended by the 1770s, the tortoise station being closed down; France introduced laws to protect the last individuals in 1771 but the animals were beyond saving by then. Very few individuals lingered on until the late 1790s; civil agent Philibert Marragon found only two tortoises in over a year of searching around 1795. No Mascarene giant tortoise have been seen alive since and, apart from a few carapaces of the Réunion and Rodrigues species and incomplete fossil carapace remains of the Mauritian species, only one stuffed Rodrigues tortoise has been preserved.
The Mascarenes once harboured the most diverse oceanic island saurian fauna anywhere, a product of radiation events and speciation. Unfortunately, little attention was given to these reptiles during the early years of Mascarene history and many had become extinct before being formally described scientifically. What was probably one of the world’s largest skinks, Leiolopisma (Didosaurus) mauritiana of Mauritius, would surely have been noticed by early travelers but was never mentioned; this suggests that the species may have already been extinct by the time the Dutch arrived in 1598. Evidence as to the huge density of reptiles that once populated mainland Mauritius is exhibited on Round Island, the only place where most of the terrestrial Mauritian reptiles now survive. Round Island is the only islet that has remained rat-free, and it was probably escaped rats from earlier voyages, e.g. Arab vessels c.13th century and Portuguese 1505, which exterminated all of the larger lizards and snakes on mainland Mauritius prior to the Dutch colonisation. Fossil remains have confirmed the existence of Round Island species on the mainland.
Mainland Mauritius was thus once inhabited by a large, diverse reptile fauna comprising: a large omnivorous skink, L. mauritiana; a second smaller but predominantly carnivorous species, Telfair’s skink Leiolopisma telfairi; a medium sized leaf-litter species, Bojer’s skink Gongylomorphus bojerii; a terrestrial night gecko, Nactus serpensinsula, with subspecies on the islets around Mauritius; and a species confined to the northern islet Gunner’s Quoin, Nactus coindemirensis. Another small species, Bouton’s skink Cryptoblepharus boutonii, although rare, still survives on the mainland. The large arboreal gecko Phelsuma guentheri, now confined to Round Island, also occurred on mainland Mauritius and recent DNA analysis has shown that the 3 other Mauritian Phelsuma species, P. ornata, P. cepediana, and P. guimbeaui comprise a number of distinct populations. All described Phelsuma species are still extant on Mauritius.
Réunion had a much less diverse lizard fauna and all the species appear to be derived from Mauritian stock. Two Phelsuma day geckos, P. inexpectata and P. borbonica were thought to be distinct subspecies of Mauritian species, but have now been given full specific status. Two skinks, Bojer’s skink Gongylomorphus bojerii and Telfair’s skink Leiolopisma telfairi are now considered extinct; the last-named from the fossil record only. Bojer’s skink was last collected in 1839 and the Phelsuma geckos were also considered extinct but were rediscovered in 1964. An introduced Malagasay snake was thought to be responsible for the demise of the Phelsuma geckos and the extinction of the skinks can probably be attributed to rats.
Rodrigues had a large and diverse saurian fauna but again, little mention has been made of them. The world’s largest gecko Phelsuma gigas, and another large species Phelsuma edwardnewtoni, were mentioned by a number of observers, and the former was described in great detail. Rodrigues is now known to have also harboured 2 endemic Nactus geckos and 2 endemic geckos of unknown affinity. Rats were a scourge to the earliest visitors on Rodrigues and probably accounted for the extinction of all of the endemic lizards on mainland Rodrigues. Cats were introduced to control rat numbers and proved to be serious predators of tortoises and probably the larger lizards.
Like Mauritius, Rodrigues has a number of islets within its lagoon and these provided refuges for the geckos long after they had disappeared from the mainland. Lienard in 1843 described Phelsuma gigas from 5 live individuals sent to him on Mauritius in 1841 from Ile aux Fregate, a large rocky islet off Rodrigues. He managed to keep one alive for several months but it refused all food except sweetened water from a spoon. The large greyish gecko with pale yellow underside and pink tongue has not been recorded since. Phelsuma edwardnewtoni had also disappeared from mainland Rodrigues by the 1870s, but survived on the lagoonal islets. As each islet became rat-infested, the geckos subsequently disappeared until two were collected on Ile aux Fregate in 1917. Ironically, the collector was Etienne Thirioux, a hairdresser and amateur naturalist from Port Louis, Mauritius who had previously discovered the most important Mauritian fossil material, e.g. the only known complete and articulated red rail Aphanapteryx bonasia, dodo Raphus cucullatus and giant skink Leiolopisma mauritiana. The Phelsuma edwardnewtoni specimens were sent to Paris where they still reside whilst Thirioux, aged 71 in 1917, died in Port Mathurin, capital of Rodrigues, in the same year. Sadly, rats finally reached Ile aux Fregate in 1918 and P. edwardnewtoni is now extinct.
Rodrigues has lost all of its endemic reptiles. Only the introduced geckos Hemidactylus frenatus, Lepidodactylus lugubris and Gehyra mutilata now survive.
Snakes (Ophidia: Boidae)
Quite extraordinarily, an endemic subfamily of snakes (Bolyerinae) comprising two taxa Casarea dussumieri, an arboreal species, and a leaf-litter burrowing species Bolyeria multicarinata is unique to Mauritius; no snakes are known to have inhabited Réunion or Rodrigues. From fossil material found in the Mare aux Songes, Casarea dussumieri has been identified along with another extinct endemic species the Mauritian blind snake, Typhlops cariei. The worm snake, Typhlina bramina, a closely related and similar species has been introduced to all three Mascarene Islands.
No accounts mention the presence of snakes on Mauritius and the islands were considered ‘blessed’ due to their absence. However, as with the lizard species, snakes certainly inhabited mainland Mauritius and were probably early victims of rats. Both snake species were found on a number of northern islets until the early 1800s but disappeared, as each islet became rat-infested. Both species survived on Round Island until comparatively recently but, due to the degradation of vegetation by rabbits and goats, Bolyeria multicarinata was last seen and photographed in 1975 and is now considered extinct.