Giant Tortoises Ruled Indian Ocean Islands Long Before Humans Surfaced, Finds Study
Looking at the evolution and spread of these animals, they found that Madagascar, Aldabra and Seychelles were home to three closely related species of giant tortoises. From these, two became extinct in the Middle Ages, a few centuries later, after Madagascar was colonised by humans.
Before humans, islands of the western Indian Ocean were mostly dwelled by giant tortoises, each weighing around 200 kilograms, reveals a report by Independent.
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This is based on research conducted by researchers from the Museum of Zoology in Dresden, Germany. Researchers looked at ancient DNA data from bones and museum specimens originating from Madagascar and neighbouring islands to look at the evolution and extinction of these creatures.
Looking at the evolution and spread of these animals, they found that Madagascar, Aldabra and Seychelles were home to three closely related species of giant tortoises. From these, two became extinct in the Middle Ages, a few centuries later, after Madagascar was colonised by humans.
According to the scientists, the species aren¡¯t related to five other species that lived on Mauritius, Reunion and Rodrigues. Around 200 years ago, the Madagascar giant tortoises also disappeared post the arrival of the first humans on the islands.
Study co-author Uwe Fritz from the Museum of Zoology explained, ¡°We often think that humans only started to wipe out species in recent times. But in reality, humans exploited local food resources and changed their environment early on. As a result, many large animal species disappeared all over the world, including most of the giant tortoise species in the western Indian Ocean.¡±
According to the researchers, the arrival of humans on the island caused a massive disturbance to the natural balance of species in the region. They offer examples of some tree samples on those islands that are currently under extinction threat since the giant tortoises disappeared.
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Dr Fritz added, ¡°This is due to the fact that the trees¡¯ seeds could only germinate once their hard shells had been partially digested by the tortoises after having been eaten. Since the disappearance of the tortoises, saplings have no longer been able to germinate. This shows that the loss of a species can trigger a fatal domino effect in the ecosystem.¡±
Looking at DNA from small pieces of bone samples, researchers could differentiate genetic material which suggests another extinct tortoise species -- Astrochelys rogerbouri-- was alive on Madagascar, which reached a ¡®carapace length¡¯ of around half a metre.
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