If you missed the Pleistocene in the Americas, you never got to see all the fantastic megafauna we once had here: mastodons, sabre tooth cats, giant sloths, hippo-rhino-looking Toxodons...and 3,000-pound armored beasts called Glyptodonts. Now a new DNA analysis reveals that Glyptodonts are extinct cousins of present-day armadillos. Except these creatures were the size of small cars and could smash you with their spiky, clubbed tails.

At least, some species of Glyptodont could smash you—others did not have clubbed tails, though all of them would have looked to our modern eyes like freakishly outsized armadillos. What's interesting is that these creatures evolved to their massive sizes in a relatively short time. The researchers, who published their findings in Current Biology, say the last common ancestor of Glyptodonts and today's armadillos was a 175-pound animal who toddled around South America about 35 million years ago.

Since that evolutionary divergence, some Glyptodonts, such as the massive Doedicurus (the one with the clubbed tail), grew to 1.5 tons in weight. They finally went extinct about 10,000 years ago.

One of the researchers, Frédéric Delsuc, said in a release that Glyptodonts are probably "a subfamily of gigantic armadillos" that went extinct. Unlike most armadillos during the Pleistocene, as well as today, Glyptodonts did not have articulated carapaces fashioned out of segments. Instead, they had what the researchers describe as a "dome-shaped, tightly-fused carapace." Basically, their bodies were covered with giant, solid shields rather than plate armor.

"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," Delsuc said. In other words, these creatures were so big that there were unique evolutionary pressures at play when it came to the structure of their carapaces. With a body that heavy, being covered in jointed segments might have been a losing proposition. A solid shield would have been more structurally sound.

Current Biology, 2016. DOI: 10.1016/j.cub.2016.01.039