Thousands of years ago, a now-extinct animal called a glyptodont lived among ground sloths and saber-toothed cats, possessing the appearance of a massive armadillo. In fact, one of the largest species, Doedicurus, weighed up to a ton and had a spikey, club-shaped tail. Now, a new study by McMaster University and the CNRS reveals the reason for their armadillo resemblance: they were armadillos.
"Glyptodonts in fact represent an extinct lineage that likely originated about 35 million years ago within the armadillo radiation," Hendrik Poinar, co-author of the study, said in a press release.
The team arrived at its conclusion by reconstructing the family tree of these ancient animals using their mitochondrial genome, which was created using small DNA fragments obtained from bits of their bony, protective carapace.
"Glyptodonts should probably be considered a subfamily of gigantic armadillos," added additional co-author Frédéric Delsuc. "We speculate that the peculiar structure of their unarticulated carapace might have evolved as a response to the functional constraint imposed by the size increase they experienced over time."
After computationally reconstructing ancestral DNA sequences based on known modern glyptodont sequences seen in living relatives, the team used RNA baits in order to fish the Doedicurus mitochondrial DNA out of an extract that was made up of other kinds of DNA from various sources.
The results showed that glyptodonts lie within the armadillo grown group, making up a unique subfamily, Glyptodontinae, within the Chlamyphoridae family that is represented today by the dwarf pink fairy armadillo and the giant armadillo. The molecular data suggests that glyptodonts diverged from armadillos in the fossil record no earlier than 25 million years ago.
The team also found that the glyptodonts' increase in size over time was extremely impressive, with records showing that they evolved from medium-sized forms weighing around 80 kilograms to true megafauna in the Pleistocene, reaching a whopping 2,000 kilograms before they vanished at the end of the last ice age.
The findings were published in the Feb. 22 issue of Current Biology.
