New research using a novel technique to recover ancient DNA reveals that the evolutionary history of glyptodonts—huge, armored mammals that went extinct in the Americas at the end of the last ice age—is unexpectedly brief.
The work, published this week in the journal Current Biology by an international team of researchers, confirms that glyptodonts likely originated less than 35 million years ago from ancestors within lineages leading directly to one of the modern armadillo families.
Numerous species of glyptodonts lived in dense forests, open grasslands, and a variety of other ecosystems, occupying a range that stretched from what is now the southern part of the United States to the Patagonia region of South America.
“Although their disappearance has been blamed on human depredation as well as climate change, some species persisted into the early part of the modern epoch, long after the disappearance of mammoths and saber-toothed cats," said Ross D.E. MacPhee, an author on the study and curator in the Museum's Department of Mammalogy. "Like the loss of giant ground sloths, mastodons, and dozens of other remarkable mammalian species, the precise cause of the New World megafaunal extinctions remains uncertain.”
Although scientists including Charles Darwin collected partial remains of glyptodonts in the early 19th century, at first nobody knew what kind of mammal they represented. It was eventually accepted that glyptodonts must be related in some way to armadillos, the only other New World mammals to develop a protective bony shell. However, because of the many physical differences between these two groups, most paleontologists have held the view that they must have separated very early in their evolutionary history.
To try and clarify this poorly understood history, researchers Frédéric Delsuc of the French National Center for Scientific Research at the University of Montpellier and Hendrik Poinar of McMaster University worked alongside MacPhee to learn what genetic information on these ancient armored animals could reveal.
As is often the case in ancient DNA investigations, fossil genomic material is poorly preserved, and only one sample worked—a carapace fragment of an undetermined species of Doedicurus, a gigantic glyptodont that lived until about 10,000 years ago. Using a novel approach to recover genetic information from ancient specimens, the team successfully assembled the complete mitochondrial genome of Doedicurus and compared it to that of all modern xenarthrans, a group of mammals including armadillos, sloths, and anteaters.
The researchers found that instead of representing a very early, independent branch of armored xenarthrans, glyptodonts likely had a much later origin, from ancestors within lineages leading to the modern armadillo family Chlamyphoridae.
More surprising still, the study finds that the closest relatives of glyptodonts—some species of which may have weighed 2 tons or more—include not only the giant armadillo (Priodontes maximus), which can weigh up to 25 pounds, but also the 4-ounce pink fairy armadillo, or pichiciego (Chlamyphorus truncatus).
“Contrary to what is generally assumed about the distinctiveness of glyptodonts, our analyses indicate that they originated only some 35 million years ago, well within the armadillo radiation,” Delsuc said. “Taxonomically, they should be regarded as no more than another subfamily of armadillos, which we can call Glyptodontinae.”