Armadillos are most closely related to anteaters and sloths, a trio that together forms the mammalian order Xenarthra. This grouping is not based on superficial resemblance; molecular studies consistently confirm that these three lineages share a common ancestor that lived tens of millions of years ago in South America. The family tree gets stranger the further back you go, connecting armadillos to elephants and aardvarks through deep evolutionary history, and forward to some of the largest armored animals that ever walked the Earth.
Anteaters and Sloths Are the Closest Living Relatives
If you lined up an armadillo, a giant anteater, and a two-toed sloth, you would be forgiven for thinking they have nothing in common. One wears bony armor, one has a long sticky tongue and shaggy fur, and one hangs upside down from branches. Yet DNA analysis places all three firmly in Xenarthra, one of the four major branches of placental mammals. Within this order, armadillos occupy their own subgroup called Cingulata, while anteaters and sloths together form a sister group called Pilosa.
Multiple independent genetic studies have confirmed this arrangement. An analysis combining nuclear and mitochondrial DNA sequences found strong support for the monophyly of Xenarthra and for the grouping of anteaters and sloths into Pilosa, with armadillos as the outgroup.1PubMed Central. The evolution of armadillos, anteaters and sloths depicted by nuclear and mitochondrial phylogenies: implications for the status of the enigmatic fossil Eurotamandua A separate study using retroposed elements, pieces of DNA that insert themselves into the genome at random and are nearly impossible to reverse, arrived at the same conclusion with near-perfect statistical support.2Molecular Biology and Evolution. Retroposed Elements and Their Flanking Regions Resolve the Evolutionary History of Xenarthran Mammals (Armadillos, Anteaters, and Sloths)
In plain terms, this means anteaters and sloths are more closely related to each other than either is to armadillos. But all three are far more closely related to one another than any of them is to, say, a mouse, a dog, or a human. Think of it as two siblings (anteaters and sloths) sharing a parent with a cousin (armadillos), all part of the same extended family that split from every other placental mammal very early on.
The Deeper Connection to Elephants and Aardvarks
Zooming out from Xenarthra, the next surprise is who armadillos are related to at the grand scale of mammalian evolution. Genome-scale studies consistently place Xenarthra as the sister group to Afrotheria, a clade of African-origin mammals that includes elephants, manatees, hyraxes, aardvarks, tenrecs, and elephant shrews. Together, Xenarthra and Afrotheria form a superorder called Atlantogenata, a name that nods to the Atlantic Ocean, which separated the continents where these two groups evolved.
This relationship was established through analyses of millions of nucleotide sites and confirmed using multiple independent lines of evidence, including retroposon insertions that serve as essentially irreversible genetic markers. A genome-wide nucleotide analysis recovered the Atlantogenata grouping with full statistical support and rejected alternative arrangements in which either Xenarthra or Afrotheria branched off alone at the base of the placental tree.3PubMed Central. The Interrelationships of Placental Mammals and the Limits of Phylogenetic Inference Another study using genomic insertions and deletions found support specifically for Atlantogenata over two competing hypotheses, and identified retroposon insertions backing this grouping with none supporting the alternatives.4PubMed Central. Using genomic data to unravel the root of the placental mammal phylogeny
The practical meaning is that armadillos are more closely related to elephants than they are to any member of Boreoeutheria, the superorder that contains rodents, bats, primates, carnivores, and most of the mammals people encounter daily. The split between Atlantogenata and Boreoeutheria represents one of the earliest forks in placental mammal evolution, likely happening when the southern continents were drifting apart from the northern ones.
Glyptodonts Were Giant Armadillos, Not Just Cousins
Among the most spectacular extinct relatives of armadillos are the glyptodonts, tank-like herbivores that roamed South America until roughly 10,000 years ago. Some species, like Doedicurus, were the size of a small car and carried a rigid dome of fused bony plates along with a spiked tail club. For a long time, scientists debated whether glyptodonts were a separate lineage that merely resembled armadillos or whether they were genuine members of the armadillo family tree.
Ancient DNA settled the question. Researchers successfully extracted and sequenced the complete mitochondrial genome of Doedicurus, and the results were unambiguous: glyptodonts are deeply nested within the armadillo crown group, not sitting alongside it as a sister lineage. Specifically, glyptodonts fall within the family Chlamyphoridae as a distinct subfamily, Glyptodontinae.5Current Biology. Mitochondrial Genomes Suggest that Extinct Glyptodonts Are Deeply Nested in the Tree of Extant Armadillos An independent molecular study went further, finding that the closest living relatives of glyptodonts are the tiny fairy armadillos of Argentina, animals that weigh barely 100 grams compared to the glyptodont’s estimated 1,500 kilograms or more.6PubMed. Ancient DNA from the extinct South American giant glyptodont Doedicurus sp. (Xenarthra: Glyptodontidae) reveals that glyptodonts evolved from Eocene armadillos
This is a genuinely remarkable finding. Imagine discovering that the largest land tortoise that ever lived was not just in the same order as a particular thumbnail-sized species, but was its closest relative. That is roughly the scale of the size disparity between glyptodonts and fairy armadillos. It also means that the heavily armored body plan armadillos are famous for is even more ancient and more variable than it appears today: the same basic blueprint produced animals ranging from pocket-sized burrowers to megafaunal giants.
Two Families of Living Armadillos
Most people think of armadillos as a single group, but living armadillos are split into two families that diverged from each other roughly 45 million years ago. That split is ancient enough that some researchers have argued it deserves the same taxonomic weight given to the divide between, say, dogs and bears. The two families are Dasypodidae, which includes the long-nosed armadillos like the familiar nine-banded armadillo, and Chlamyphoridae, which encompasses a broader range including fairy armadillos, three-banded armadillos, giant armadillos, and the six-banded armadillo.
A mitogenomic study estimated that the first split within armadillos, separating the long-nosed armadillos (Dasypodinae) from all other subfamilies, occurred around 45 million years ago. Given this remarkably ancient divergence, the authors proposed formally recognizing the two-family classification.7Molecular Biology and Evolution. Shotgun Mitogenomics Provides a Reference Phylogenetic Framework and Timescale for Living Xenarthrans Within Chlamyphoridae, fairy armadillos (subfamily Chlamyphorinae) are closely allied with tolypeutine armadillos, which include the three-banded armadillos and the giant armadillo.2Molecular Biology and Evolution. Retroposed Elements and Their Flanking Regions Resolve the Evolutionary History of Xenarthran Mammals (Armadillos, Anteaters, and Sloths)
The fairy armadillos themselves are among the most enigmatic mammals alive. The pink fairy armadillo of central Argentina is almost entirely subterranean, and so rarely seen that basic aspects of its biology remain poorly understood. Molecular phylogenetics revealed that the two fairy armadillo species form a single lineage whose burrowing lifestyle probably evolved in response to the drying of South American environments during the Oligocene, around 32 million years ago.8PubMed. Molecular phylogenetics unveils the ancient evolutionary origins of the enigmatic fairy armadillos
Why Armadillos Are Not Related to Pangolins
One of the most persistent misconceptions about armadillos is that they must be related to pangolins, the scaly anteaters of Africa and Asia. Both animals are covered in tough, overlapping structures. Both curl up for protection. Both eat insects. The resemblance is striking enough that historical naturalists sometimes classified them together. But genetically, armadillos and pangolins are about as distantly related as two placental mammals can be.
Pangolins belong to the order Pholidota, which falls within the superorder Laurasiatheria, placing them closer to carnivores (cats, dogs, bears) than to any xenarthran. The armor itself evolved independently. Armadillo shells are made of bony plates called osteoderms, true bone that forms within the skin through a process similar to how skull bones develop.9PubMed. Osteoderm morphology and development in the nine-banded armadillo, Dasypus novemcinctus (Mammalia, Xenarthra, Cingulata) Pangolin scales, by contrast, are made of keratin, the same protein that makes up human fingernails and rhino horns. The two structures have completely different developmental origins and tissue compositions.
Genomic research has documented that distantly related mammals with similar skin coverings share certain convergent changes in their DNA, suggesting that evolution sometimes arrives at similar-looking solutions through partly overlapping genetic pathways.10SpringerLink / Science China Life Sciences. Genome-wide signatures of mammalian skin covering evolution But convergent evolution is the key phrase: the armor of armadillos and the scales of pangolins are analogous structures, not inherited from a shared armored ancestor.
What Makes Xenarthrans a Real Group
Given how different armadillos, anteaters, and sloths look from each other, it is fair to wonder what originally tipped off anatomists that they belong together. The name Xenarthra itself provides a clue. It comes from Greek words meaning “strange joints” and refers to a set of extra bony articulations between the vertebrae in the lower back, structures found in all xenarthrans and in no other living mammals. These extra joints are thought to stiffen the spine, which is useful for the powerful digging that characterizes armadillos and many of their relatives.11PubMed. Vertebral bending mechanics and xenarthrous morphology in the nine-banded armadillo (Dasypus novemcinctus)
Osteoderms, the bony skin plates, are another shared feature with deep roots in xenarthran evolution, though they are best developed in armadillos and their extinct relatives. Even some extinct sloths had osteoderms. A comparative study found that the extinct mylodontid ground sloths had simple, isolated bony skin nodules and proposed that this condition is likely the ancestral state for Xenarthra as a whole. The highly organized, interlocking osteoderm patterns seen in armadillos and glyptodonts are more derived versions of this same basic feature.12PubMed. Comparative anatomy and histology of xenarthran osteoderms
Xenarthrans also share other unusual traits: reduced or absent teeth (anteaters have lost them entirely, armadillos have simple peg-like teeth without enamel, and sloths have a reduced set), low metabolic rates compared to most placental mammals, and unusually low and variable body temperatures. These features are not just random quirks; they reflect a shared evolutionary trajectory shaped by millions of years of isolation on the South American landmass.
South America as the Cradle of Xenarthran Evolution
The story of xenarthran origins is inseparable from the geological history of South America. After the breakup of the supercontinent Gondwana, South America spent most of the last 60 million years as an island continent, connected to neither North America nor Africa. During this long isolation, xenarthrans diversified spectacularly. They produced giant ground sloths the size of elephants, armored glyptodonts, a dizzying variety of armadillos, and multiple lineages of anteaters.
Molecular clock studies have linked key diversification events within Xenarthra to major climate shifts and tectonic changes on the continent. A relaxed molecular clock analysis found that independent xenarthran lineages appear to have diversified at roughly the same times, suggesting that shared environmental pressures like the uplift of the Andes or shifts in global temperature were driving speciation across the group simultaneously.13PubMed Central. Influence of Tertiary paleoenvironmental changes on the diversification of South American mammals: a relaxed molecular clock study within xenarthrans
The fossil record for the earliest xenarthrans remains frustratingly thin. No unambiguous xenarthran fossils have been found from the Paleocene, and Eocene remains consist almost entirely of isolated armadillo osteoderms and postcranial bones of uncertain placement.14Journal of Mammalogy. Paleogene Xenarthra and the evolution of South American mammals The earliest definitive xenarthran material thus comes from around 55 to 50 million years ago, but molecular estimates suggest the group itself may be older than that, originating somewhere in the late Cretaceous or earliest Paleocene. This gap between the molecular estimates and the fossil evidence is a common frustration in mammalian paleontology, especially for groups whose early members were small and lived in environments where fossilization was unlikely.
When the Isthmus of Panama formed roughly 3 million years ago, connecting North and South America, xenarthrans were among the groups that migrated northward in what is called the Great American Biotic Interchange. The nine-banded armadillo is the most successful modern example, having spread as far north as the central United States and continuing to expand its range.
Unexpected Physiology
The low metabolic rate shared by xenarthrans has some surprising consequences. While most people associate hibernation with bears or ground squirrels, at least one armadillo species is a genuine hibernator. The pichi, a small armadillo from Patagonia, enters extended torpor bouts during winter that last about 75 hours each, with its body temperature dropping to around 15°C. Between hibernation bouts, it rewarms to about 29°C before entering torpor again. Outside the hibernation season, it also uses shorter bouts of daily torpor lasting four to six hours.15PubMed Central. Hibernation and daily torpor in an armadillo, the pichi (Zaedyus pichiy)
This makes the pichi the only armadillo confirmed to be a true hibernator, and it underscores how xenarthran physiology departs from what most people expect of a tropical mammalian group. The low and variable body temperatures seen across xenarthrans are likely an ancestral trait rather than a recent adaptation, one that connects to the group’s early evolution on a continent where ecological conditions have swung dramatically over geological time.
The nine-banded armadillo has its own physiological claim to fame: it is one of the few non-human animals that can naturally harbor the bacterium that causes leprosy. This susceptibility is linked to the armadillo’s unusually low body temperature, which provides an environment where the slow-growing pathogen can thrive. While this is a quirk of one species rather than a xenarthran-wide trait, it has made the nine-banded armadillo an important animal in biomedical research, giving it a role in science that extends well beyond evolutionary biology.
How Modern Armadillo Diversity Compares to the Past
Today there are around 20 recognized species of armadillo, ranging from the pink fairy armadillo at roughly 12 centimeters long to the giant armadillo, which can exceed a meter in body length and weigh over 30 kilograms. That seems like decent variety until you consider what the fossil record reveals. During the Pleistocene, South America was home to dozens of armadillo species plus the entire glyptodont radiation, ground sloths in multiple families, and several distinct lineages of anteaters. Modern xenarthrans represent a small surviving fraction of what was once a far more diverse group.
The extinction of the megafauna at the end of the Pleistocene hit xenarthrans especially hard. Glyptodonts, giant ground sloths, and the largest armadillo species all vanished. What remains today are predominantly small to medium-bodied species. The giant armadillo is the largest living xenarthran, and it is modest compared to even mid-sized glyptodonts. The anteater lineage is down to four species, and sloths are represented by just six species in two genera, which are not even each other’s closest relatives among sloths (living two-toed and three-toed sloths evolved their tree-dwelling habits independently from different ground sloth ancestors).
This means that when you look at a nine-banded armadillo shuffling across a suburban lawn, you are seeing one twig of a once-enormous evolutionary bush. Its closest relatives include a tiny pink burrower it has never met, a two-ton armored giant that went extinct a few thousand years ago, a sloth hanging from a cecropia tree in Costa Rica, and a giant anteater striding across the Brazilian cerrado. And further back, its evolutionary cousins include elephants roaming the African savanna and manatees drifting through Florida’s springs. Few mammals carry such an unexpectedly sprawling family tree.