Episode 153 – Armadillos

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Body armor is a rarity among mammals, and yet this particular group has made it work in modest modern species and gigantic ancient ones. This episode, we discuss the past and present of Armadillos.

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Armored Mammals

Armadillos are strange and fascinating mammals. They belong to a group called Xenarthra, whose other members – sloths and anteaters – are also strange and fascinating. Armadillos share their cousins’ simple teeth and powerful clawed forelimbs, and they are set apart by their most famous feature: the multi-sectioned armor that covers most of their bodies. This armor is made up of many tiny osteoderms (skin bones, as also seen in crocodilians, turtles, ankylosaurs, and more) that cover parts of their head, back, and tail.

Top left: Nine-banded armadillo. Image by birdphotos.com, CC BY 3.0
Top right: Pink fairy armadillo. Image by Cliff, CC BY 2.0
Bottom left: Giant armadillo. Image by Mamíferos de Colombia, CC BY-NC 2.0
Bottom right: Three-banded armadillo. Image by Ltshears, CC BY-SA 3.0
Armadillo bones! Note the short, robust forelimbs and simple peg-like teeth. Also that armor!
Top: Nine-banded armadillo skeleton. Image by Ellenm1, CC BY-NC 2.0
Bottom: Seven-banded armadillo skull. Image by Lukas Large, CC BY-SA 2.0
Three-banded armadillos are the only species with the habit of rolling into a ball, and what a defensive strategy it is!
Left image by Sandstein, CC BY 3.0. Right image by Polyoutis, CC BY-SA 4.0

The lineage of mammals that includes armadillos – the Cingulata – has been around for at least 60 million years or so, and for most of that time, they were restricted to the isolated continent of South America, along with the other xenarthrans. The fossil record of Cingulata includes numerous well-preserved skulls and skeletons, as well as lots of fossilized osteoderms. Ancient armadillos were quite diverse, including a variety of familiar-looking forms as well as oddities like the strange horned armadillos and the gigantic igloo-shaped glyptodonts.

Among the most unusual ancient armadillos (or armadillo cousins) are the Peltephilidae or “horned armadillos.” These are most well-known from the Miocene Epoch, and they sported a pair of small horns on their noses.
Left: Art of Peltephilus by Apokryltaros, CC BY-SA 3.0
Right: Sketch of Peltephilus skull from Internet Archive Book Images

Perhaps the most famous ancient armadillos are pampatheres and glyptodonts. Pampatheres had segmented armor like modern armadillos, while glyptodonts tended to have a single turtle-like shell of armor and sometimes spiky tail weapons. Both groups existed for tens of millions of years right up to the end of the Ice Age, both were groups of armored herbivores, and both grew quite large – the largest pampatheres would have weighed hundreds of kilograms, while the very largest glyptodonts were the size and weight of cars.

Top: The Pleistocene pampathere Holmesina. Image by MCDinosaurhunter, CC BY-SA 3.0
Bottom: The Pleistocene glyptodont Glyptodon. Image by Arent, CC BY-SA 3.0

Around three million years ago, a new connection between South and North America led to the Great American Biotic Interchange, during which many groups dispersed across the two previously-separated continents. After tens of millions of years of isolation, this event allowed armadillos to move into North America for the first time. For a few million years during the Ice Age of the Pleistocene Epoch, North America was home to its very own glyptodonts and pampatheres. Sadly, the big species vanished at the end of the Pleistocene, but modern armadillos persist in both South and North America.

Learn More

Remarkable Creatures (ancient giant armadillos), Twilight Beasts

The giant armadillos of the Americas

The Xenarthrans: Armadillos, Glyptodonts, Anteaters, and Sloths (technical, paywall)

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