Once upon a time in South America, when giant ground sloths and saber-toothed cats roamed the land, another visually striking creature was plodding around: the glyptodont. This fearsome, armadillo-like animal weighed around as much as a tonne, and wielded a powerful, club-shaped, spiky tale. A new study published in the journal Current Biology has finally pinpointed where this strange beast lies on the evolutionary tree.
Based on fossil evidence, these lumbering, extinct creatures first evolved during the Eocene epoch, somewhere between 56 and 34 million years ago. They had a tortoise-like body armor, comprised of layered bony deposits within their skin; although they weren’t able to withdraw their heads for protection, they were adorned with a bony cap of armored skin on top of their skull.
This family was comprised of several genera, including the Glyptodon, which was roughly the size and mass of a Volkswagen Beetle. Although it was clear that these herbivorous animals belonged to the superorder Xenarthra, a group of mammals that includes anteaters, tree sloths and armadillos, researchers were unsure of where they fitted in here – or precisely when they evolved.
This new study, spearheaded by researchers at McMaster University in Canada and the National Center for Scientific Research in France, aimed to definitively solve this conundrum. They decided to look for the DNA of one of the largest glyptodonts, the Doedicurus, within its living relatives. This particular family member, which weighed around 1.36 tonnes (1.5 tons), was one of the last to become extinct, right at the end of the last ice age 12,000 years ago.
A fossil of a Glyptodon asper, located in the Natural History Museum of Vienna, Austria. Arent/Wikimedia Commons; CC BY-SA 3.0
By comparing the DNA extracted from a Doedicurus fossil bone to the DNA assemblages of every living Xenarthra member, the team was able to reconstruct its genetic history. As the researchers suspected, Doedicurus wasn't just related to armadillos – it belonged to the same evolutionary group, making them bonafide, ancient, giant armadillos.
They were also able to date when the family first appeared. “Glyptodonts in fact represent an extinct lineage that likely originated about 35 million years ago within the armadillo radiation,” said Hendrik Poinar, a professor of physical anthropology at McMaster University in Canada and co-author of the study, in a statement.
This date corroborates with the best fossil evidence: The remains of the oldest glyptodont family member, the Glyptatelus, was previously estimated to be 36-38 million years of age.
This study also reveals how dramatically the size of the glyptodonts changed over evolutionary time. The last common ancestor of the glyptodonts and the modern armadillo weighed in at around a measly six kilograms (13.3 pounds). Some of the last surviving members weighed at least 2,000 kilograms (4,410 pounds), about as much as an Indian rhinoceros. This means that they experienced an increase in mass of about 333 percent until they became extinct.
It was clear that these animals had a particularly peculiar evolutionary history. If rapid climate change and human activity hadn’t wiped them from the planet, who knows what bizarre, bombastic beasts these huge, herbivorous and ultimately heavy creatures would have continued to evolve into?