March, 1903.] 



KNOWLEDGE 



55 



during late Tertiary times of giaut land-tortoises in Ni^rth 

 America, while a few fragments of shell attest the former 

 occiureiicc of another species iu Patagonia. It may lie 

 therefore assumed that during the Pliocene, and, perhaps, 

 a portion of the Miocene epoch, laud-tortoises of huge 

 size were spread over the greater portion of the warmer 

 countries of the globe. 



With, or before, the close of the Pliocene division of 

 geological time, these great reptiles seem, however, to 

 have utterly vanished from all the continents of the 

 world, and to have continued to exist only in certain 

 islands, from some of which they likewise disappeared 

 before, or during the early portion of, the historic period, 

 while others have become extinct quite recently. Whether 

 these island giant tortoises are the direct descendants of 

 the species which once inhabited the nearest continents, or 

 whether they have been independently developed from 

 smaller forms in or near their own habitats, is a question 

 by n<j means easy to answer. Neither is it any less difficult 

 to account for tlie complete disappearance (apparently 

 without human intervention) of all the continental forms. 

 Although the Siwalik mastodons, elephants, sivatheres, 

 giraffes, hippopotamuses, and other large mammals, all 

 died off. yet many of them left descendants (collateral or 

 direct) in either India or Africa ; and this makes it the 

 more strange that not a single descendant of any of the 

 Pliocene giant land-tortoises should have survived in any 

 one of the five continents. Such, however, is the case, 

 explain it how we may. 



Since the Pliocene epoch, giant tortoises have been 

 restricted to two widely-sundered groups of islands. In 

 modern times the islands most famous for these tortoises 

 are those of the Galapagos group, which take their title 

 from one of the Spanish names ((jaMparjo) for a tortoise, 

 and ai'e situated on the equator, a comparatively short 

 distance ofC the western coast of South America. All the 

 other " tortoise-islands " ai-e in the Indian Ocean, where 

 they lie (with the exception of the lower extremity of 

 Madagascar) within the southern tropic, off the African 

 coast. By far the largest of these islands is Madagascar, 

 which has long been inhabited by man, and from which 

 the tortoises (perhaps in consequence of his occupation) 

 disajipeared long before the historic period, being known 

 to us otdy by their sub-fossilised remains. Between the 

 northern point of Madagascar and Africa lie the islands of 

 the Comoro group, which had also native inhabitants of 

 their own ; and fi'cni these islands the tortoises likewise 

 disappeared at an early date. All the other tortoise-islands 

 in the Indian Ocean were inhabited. They include the 

 Aldabra group, north-west of Madagascar, where the few 

 tortoises now remaining in the south island are under 

 Government protection, the Mascarenhas, or Mascarene 

 group (Reunion, or Bourbon, Mauritius, aud Rodriquez), 

 the Amirantes, and the Seychelles. None of the Mascarene 

 species survive in their proper home, and were long thought 

 to bo extinct, although a specimen has turned up from 

 a distant island, to which it had been caiTied. Much the 

 same may be said with regard to the Seychelle tortoises, 

 which were exterminated long ago in their projier habitat. 

 There seems, however, to be good reason for believing that 

 a few survivors of the species have been preserved in 

 islands to which they had hcon transported in ships. This 

 trans] Mirtation of tortoises from one island to another has 

 indeed added considerably to the difficulty of unravelling 

 the conijilicated history of the group ; a specimen of 

 the South Aldabra tortoise having been carried to one of 

 the islands of the Chagos group, to the south of Maldives, 

 whence it was subsequently transported to Mauritius. 



The accounts left by the early voyagers show t hat in the 

 Mascarene aud other islands of the Indian Ocean, as well 



as in those of the Galapagos group, the tortoises formerly 

 existed in enormous numbers. As regards the Galapagos 

 islands, it is remarkable that there are no small-.sized 

 species ; and the same holds good for the islands of the 

 Indian Ocean, with the exception of Madagascar, where 

 there is one comparatively small form (T. radiata). It 

 should be added that, if we except Madagascar (where 

 there is one moderate-sized carnivore), none of the tortoise- 

 islands were ever the home of large and predatory 

 mammals. This naturally suggests the idea that the 

 survival in these islands o£ the reptiles under consideration 

 is entirely due to the absence of such mammals. But, on 

 the other hand, it has to be borne in mind that the giant 

 Siwalik tortoise lived iu a land where large mammals — 

 both carnivorous and herbivorous — absolutely swarmed ; 

 and the same was also the case with the other extinct 

 continental sjjecies referred to above. Moreover, we have 

 no evidence of the existence of large tortoises on the 

 continents of the world at an epoch before the advent of 

 large mammals. Still, the absence of the latter from 

 practically all the tortoise-islands is a fact that cannot be 

 disregarded, and must almost certainly have had a very 

 great influence on the development of their chelonian 

 inhabitants. 



Great South Aldabra Tortoise (Tesfado daw/nn). fr.n. a specimen 

 recently living iu the London Zoological Gardens, aud now preserved 

 iu the Museum at Tring. 



In regard to the numbers iu which giant tortoises 

 formerly existed on the islands of the Indian. Ocean, very 

 few words must suffice. Writing in 1(J91, the French 

 traveller Francois Leguat states that in Kodi'iquez the 

 tortoises covered the ground so thickly that in pLices you 

 might walk a hundred paces or more by stopping from the 

 back of one on to that of another. In Mauritius, though 

 apparently less abundant, they were still very numerous 

 down to 1740 ; and there is ample testimony that during the 

 seventetmth and eighteenth centuries they also swarmed 

 on Reunion, although not a single specimen of the species 

 indigenous to that island has been preserved. The ease 

 with which these reptiles could be captured and carried 

 off, and the fiR-ility with which they coiild be kept alive on 

 board, coupled with the large amoimt of excellent meat 

 yielded by each, rendered them a valuable food-supply to 

 the crews of ships, and it was far from uncommon for 

 vessels leaving Mauritius to carry off a cargo of four 

 hundred at a time, while in 1759 one of four vessels 

 specially engaged in carrying tortoises from Rodriquez to 

 Mauritius took six thousand at once. Such a drain could 

 not but tell rapidly on the supjily, and by the early part of 

 the last century the Mascarenes were denuded of their 

 tortoise-l'auua. 



