The western part of the Indian Ocean was inhabited by various species of giant tortoise till the first half of the 20th century. The Mascarene tortoises became extinct in the year 1795. However, the Madagascar- Seychelles giant tortoise, the Dipsochelys still survives. There are fragmentary remains of the Madagascan giant tortoises, dating back to even1,25,000 years.
History of evolution of the giant tortoise, Dipsochelys
Recent revisions in the research related to the evolutionary history of this particular species of giant tortoise have been made on the basis of additional evidence. Two alternative conclusions can be drawn from the researchers. It is possible that the genus, after evolving in Seychelles, colonized Madagascar which later served as the birthplace of several species of giant tortoises. Another probable situation is that the genus evolved in the islands of Madagascar and then started colonizing other nearby islands. In both of these two possible conclusions, Madagascar has a key role to play.
The Aldabran population’s source is indeed the Madagascar Islands because of its closeness to other island groups. For occasional colonization, a close origin population is extremely important- something that Madagascar was capable of providing. The giant tortoise species of Madagascar are distinctive as Albadra’s fossil remains are mostly of D. dussumieri or species that have several resemblances with the same. Some of the potential places from where this immigration came were Comoros, Madagascar, Seychelles and two other low-lying islands, namely, Comoledo and Astove. Mention should also be made of Farquhar in this respect.
In the past 150,000 years, recolonization events have taken place minimum three times. Each such colonization could have been made possible by just one female landing. Immigration was a significant contribution to the population of giant tortoise in the Aldabra group of islands.
The recent condition of the giant tortoises
Due to their contact with human beings, all species of giant tortoise have declined in the world. The first species to have disappeared is Comoros and giant tortoises of Madagascar in between 750 A.D. and 1000 A.D. In the year 1663, colonization of the Mascarenes took place. The last giant tortoise of the Cylindraspis species has been extinct in the year 1840. The wild populations of Seychelles persisted much longer and the Aldabran belong to the category of surviving giant tortoises at present.
In Seychelles, as many as 13,000 species of giant tortoises have been removed. In the year 1787, a survey was conducted which proved that minimum 10,000 tortoises were exported from their natural habitat to other parts of the world by the end of that year.
So, a very brief history of these islands’ colonization has seen the evolution and extinction of several species of giant tortoises. The history weaves the tale of the pensive stages of extinction of these ancient creatures that have inhabited the earth for centuries. It is high time that human beings take significant steps to reduce activities that threaten the elimination of giant tortoise species from the face of the earth.