The glyptodont – an armoured mammal that was roughly the same size and weight of a Volkswagen Beetle and that lived during the Pleistocene epoch (1.8 million years ago to 11,700 years ago) – appears to be closely related to the modern armadillo, based on a new genetic analysis.
Glyptodonts lived on Earth for millions years, but eventually went extinct about 10,000 years ago, during the last glacial period (also known as the Ice Age). Until now, researchers have not been sure how to fit the glyptodont into the armadillo family tree. Glyptodonts are part of the mammal group Xenarthra that includes: extinct pampatheres, extinct ground sloths, tree sloths, anteaters, and armadillos.
The animals had squat limbs and rounded shells, which were made of more than one thousand 2.5 cm-thick bony plates known as osteoderms. They are thought to have originated in South America; fossilised remains were found in Argentina, Brazil, Uruguay, and more. G. clavipes – a species of Glyptodon – had the largest range in Brazil. Glyptodonts measured almost eleven feet in lengths (about 3.3 m) and five feet in height (1.5 m). Their tails – which the animals could swing powerfully – were also covered in bony rings.
Hendrik Poinar, an evolutionary geneticist and physical anthropologist and director of the Ancient DNA Centre at McMaster University in Hamilton, Ontario, said that the new findings shed some light on the familial relations of glyptodonts with the other mammals from the Xenarthra group.
In the new study – published on Monday (Feb. 22) in the online journal Current Biology – the researchers conducted genetic analysis and found that the glyptodonts are in fact close relative of armadillos.
According to Poinar, they have originated about 35 million years ago and represent an extinct lineage within the diversification of armadillos. To collect glyptodont specimens, Poinar worked along with an international team of scientists.
Poinar and fellow scientists used DNA extraction techniques on the bony shell of a 12,000-year-old Doedicurus (found in Argentina) – which is the largest glyptodont specimen found so far. The scientists extracted and sequenced the mitochondrial DNA – which is passed down to the offspring through the maternal line – and then compared it with the mitochondrial DNA of mammals from the Xenarthra group that are alive today.
Examining ancient DNA can help shed some light on the phylogenetic position of extinct mammals. The phylogenetic position (on the phylogenetic tree) shows the evolutionary relationships among various biological species, according to Poinar. However, the most difficult part of the process is to obtain usable DNA from fossilized specimens, he added. For the new study, Poinar and the other scientists used a technical trick to get the DNA fragment and then reconstruct the mitochondrial genome.
Moreover, the scientists also found that there was a common ancestor shared by both modern armadillos and glyptodonts, which weighed about thirteen pounds (six kilograms) – a lot less than glyptodonts weighed. Based on fossil records, glyptodonts first weighed about 176 pounds (eighthly kilograms), but then eventually evolved into animals that weighed as much as 4,400 pounds (about 2000 kg or two tons), scientists said.
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