The extinct giant tortoise was the “mammoth” of Madagascar 1,000 years ago
At least a millennium ago, a giant tortoise crept across Madagascar, grazing on plants on board—a bountiful diet that made it rewarding for mammoths and other herbivores. A new study finds that this previously unknown giant tortoise, like the mammoth, is now extinct.
Scientists discovered this species while studying fuzzy turtles that live in Madagascar and other islands in the western Indian Ocean. After stumbling across a single tibia (lower leg bone) of an extinct turtle, they analyzed the nucleus and mitochondria. DNA They determined that the animal was a newly discovered species, and named it after it Astrocheles rogburyAccording to the study, published Jan. 11 in the journal Science advances (Opens in a new tab). The turtle species name honors the late Roger Burr (1947-2020), French herpetologist and expert on giant tortoises of the western Indian Ocean.
It is unclear when the newly discovered species became extinct, but the studied specimen appears to be about 1,000 years old. “As we get better and better technology, we are able to provide different types of data that often change our perspective,” said a co-author of the study. Karen Sammonds (Opens in a new tab), an associate professor in the Department of Biological Sciences at Northern Illinois University, told Live Science. “It’s really exciting to discover a new member of the community.”
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The volcanic islands and atolls across the western Indian Ocean were teeming with giant tortoises. Weighing in at up to 600 pounds (272 kilograms), these massive megafauna have greatly impacted their ecosystems, if only through their voracious appetites. Today, 100,000 giant tortoises still live on Aldabra – a green atoll northwest of Madagascar – consuming 26 million pounds (11.8 million kg) of plant matter each year.
Most of the species native to that region are now extinct due to human activities, and paleontologists still struggle to piece together the story of these ancient turtles. But analysis of the ancient DNA of these giants offers a way forward, which in turn sheds light on prehistoric island life.
“If we want to know what these island ecosystems were originally like, we need to include giant tortoises — large, extinct members of the ecosystem that took on a role often occupied by large grazing mammals,” Sammonds said. “And in order to understand the key role they played, we need to understand how many turtles are out there, where they lived, and how they got there.”
By the time explorers began collecting giant tortoise fossils in the 17th century, the giant tortoise’s indigenous population of Madagascar had long since disappeared–likely victims of colonization by the Indo-Malays 1,000 years ago–and their relatives swarmed the Mascarene archipelago and the Granite Seychelles. . They live on lost time. European sailors harvested turtles for food and “turtle oil,” and all but those in remote Aldabra were gone by the 19th century.
The difficult task of reconstructing their history falls to modern paleontologists. “The tortoise remains are remarkably fragmentary, and I’m a real challenge to figure out what a tortoise looks like from part of a shell,” said Sammonds. Scientists have also struggled to make sense of the fossil record distorted by the turtle trade. Did a particular specimen found at Mascarene originate there, or was its carcass dumped by a ship from the Granitic Seychelles?
“In the end, a lot of these fossils just sat in a closet, unused and unconsidered,” said Sammonds. But recent technological advances in ancient DNA analysis have given Sammonds and colleagues a glimpse inside the turtle’s black box. evolutionary History. “It’s exciting that we now have this technology and can use ancient DNA to put these broken fossil pieces to good use.”
For the study, Sammonds and his colleagues produced nearly complete mitochondrial genomes from several turtle fossils, some of which were hundreds of years old. By combining these sequences with previous data on the tortoise’s pedigree Radiocarbonthe team was able to describe how giant tortoises migrated to many islands of the Indian Ocean.
For example, the extinct Mascarene lineage Cylindraspis appears to have left Africa in the late Eocene, more than 33 million years ago, and settled the now-sunken volcanic region of Reunion. From there, the species spread around the local islands, leading to the divergence of five species of Mascarene tortoise between 4 million and 27 million years ago.
Samonds hopes that future paleontological studies will follow the example of the current work and benefit from incorporating ancient DNA analyzes into more traditional methodologies.
“Including ancient DNA allowed us to examine how many species of turtles there are and what their relationships are with one another,” said Sammonds. “It also helped us estimate the indigenous diversity of turtles on these islands.” “We couldn’t have explored these topics before.”