Armadillo Empire, Part 2: Fairies, Tolypeutines, and Where Glyptodonts Go

Once more, it’s time to look at armadillos, both at their diversity and at some aspects of their evolutionary history…

Caption: the evolution of tiny burrowing forms (look for the fairy armadillo at lower left) and giant, heavily armoured, herbivorous forms (like the giant glyptodont Doedicurus) means that armadillos exhibit a really profound, and rarely commented on, variation in size. Images: James Dana, Hermann Burmeister; both in public domain.

If you read the previous article – which you really should have done by now, come on – you’ll have noticed my repeated emphasis of the fact that the mostly large, mostly herbivorous, entirely extinct glyptodonts (and a few related groups of large-bodied, armoured xenarthrans) are deeply nested within the armadillo radiation. They are armadillos, not a separate group. That’s quite the surprise relative to convention, because the ‘standard view’ – repeated in all classic and even some modern texts on fossil mammal diversity (e.g., Prothero 2017) – is that glyptodonts and armadillos share a long-ago ancestry, and that the two groups are close… not that one is nested within the other.

If you pay attention to discoveries relevant to the world of fossil mammals, you might have heard that the placing of glyptodonts within armadillos is a discovery we owe to molecular phylogenetics. In 2016, Frédéric Delsuc and colleagues published the results of a molecular analysis of armadillo phylogeny, incorporating palaeogenomic data from the Pleistocene-Holocene giant glyptodont Doedicurus (Delsuc et al. 2016). Their primary take-home was that glyptodonts “are not … a sister group [to armadillos], but a subfamily”, “firmly within the family tree of modern armadillos”, according to this article at BBC News. More recent molecular studies have provided additional support for this view (Brambilla et al. 2025).

Don’t get me wrong: none of the discussion or reporting surrounding this study has been technically wrong, nor notably misleading. But it’s certainly created the impression that glyptodonts were universally regarded as the ‘armadillo sister group’ prior to this gene-based work.

Caption: armadillo skulls are highly variable, and contain a ton of anatomical information that can be analysed within a phylogenetic context. If you do analyse this data and include sufficient taxa… what do you find? Not enough people have paid attention to the article shown at left (Gaudin & Wible 2006); read on. The skull diagrams here, from Gaudin & Wible (2006), are (clockwise from upper left) Dasypus, Tolypeutes, Proeutatus, Cabassous.

We need to push back on this a bit: the finding that glyptodonts are crown-armadillos, surrounded by extant lineages, doesn’t ‘belong’ to the world of molecular phylogenetics, and I say this based on statements made by palaeontologists interested in anatomy (and not working on palaeogenomics). George Engelmann (1978, 1985) was first to imply this, initially in his 1978 PhD thesis, since he argued that the extinct eutatines (conventionally regarded as euphractines, and hence close to the living hairy armadillos and kin: see the previous article) were closer to glyptodonts than to other armadillos… a discovery which implied paraphyly among ‘conventional’ armadillos.

Building on this work, Gaudin & Wible (2006) went further, and argued that craniodental data showed that glyptodonts (and the also extinct pampatheres) were closer to living euphractines than to both eutatines and the living long-nosed armadillos. In their 2011 study on the Late Oligocene tolypeutine Kuntinaru of Bolivia, Billet et al. (2011) reported similar findings.

Caption: an armadillo cladogram published by Tim Gaudin and John Wible in 2006, and emphasizing the fact that phylogenetic hypotheses whereby glyptodonts (and pampatheres and their kin) are nested within crown-armadillos are not ‘owned’ by molecular biologists. Anatomists discovered this first! Images: three-banded armadillo in the public domain (original here); Eutatus from Krmpotic et al. (2009); Macroeuphractus from Vizcaíno & De Iuliis (2003); Euphractus and glyptodont by Darren Naish.

I remember reading Gaudin & Wible (2006) when it was new and thinking it so heterodox that it surely couldn’t be right. I mean: we know that glyptodonts are the sister-group to living armadillos, right? Nope... glyptodonts have been considered nested within crown-armadillos since the 2000s. All of which means that it’s wrong to frame the nesting of glyptodonts within crown-armadillos as a surprising, molecular-led discovery.

Caption: I’ve mentioned a few times how pleased I am to own the museum-quality model of the Pliocene-Pleistocene-Holocene glyptodont Neosclerocalyptus shown here, created by Santiago Druetta in Córdoba, Argentina. Thanks to Rebecca Groom for printing and painting. At right, a Glyptodon clavipes skull photographed at the Oxford University Museum of Natural History. Note the massive jugal flange and deep and broad nose. Images: Darren Naish.

On the need for an expanded taxonomy of armadillos. I have one final thing to say on the phylogenetic position of glyptodonts, and it concerns taxonomy. In those phylogenetic schemes where glyptodonts are the sister-group to other armadillos, they’ve traditionally been given their own ‘higher order’ name, this variously being Glyptodontia, Glyptodontoidea or Glyptodonta (McKenna & Bell 1997, Vizcaíno & Bargo 1998, Gaudin & Wible 2006).

But the discovery that glyptodonts belong within crown-armadillos – and, specifically, are surrounded by euphractines and tolypeutines (Delsuc et al. 2016) – has led to the implication that they should be absorbed into Chlamyphoridae (see the discussion in this Tet Zoo article), a group formulated as if it’s a Linnaean ‘family’. How inclusive or otherwise a ‘family-level’ clade should be is wholly subjective, and there might well be some specialist workers entirely happy with the idea that all the lineages concerned (eutatines, euphractines, glyptodonts, pampatheres, fairy armadillos and tolypeutines) should indeed be lumped into a super-inclusive Chlamyphoridae.

Caption: a molecular armadillo phylogeny as published by Delsuc et al. (2016). The phylogeny is broadly consistent with other studies and other data (though don’t go thinking that all phylogenetic studies on armadillos are in agreement — oh ho ho!), but the issue I have with what’s shown here is the taxonomy… should we really be including all those lineages within a super-inclusive Chlamyphoridae? Image: Delsuc et al. (2016).

But I’m not happy with it. I think that glyptodonts are absolutely ‘distinct enough’ (and diverse enough, and geologically old enough) to warrant ‘higher-order’ taxonomic distinction, and I think it’s helpful to have them differentiated from pampatheres (Pampatheriidae) and from the clade that includes fairy armadillos and tolypeutines. Those last two could be united within Chlamyphoridae. If the extinct eutatines and the extant euphractines are outside the glyptodont + chlamyphorid clade, they need ‘higher-order’ names too, so here’s a push to have us recognise Eutatidae and Euphractidae…. if the phylogenetic hypotheses I’m using here as a framework remain robust.

Fairy armadillos or Pichiceigos. Arguably the most specialized and unusual armadillos are the fairy armadillos, generally regarded these days as a clade (Chlamyphorinae) that shares a Late Eocene or Oligocene ancestor with tolypeutines (e.g., Billet et al. 2011, Delsuc et al. 2012, 2016, Gibb et al. 2016). Anatomical evidence previously suggested that fairy armadillos belong with euphractines – this group was termed Euphracta by Engelmann (1978, 1985) – since all are alike in the bony anatomy of the ear region, most memorably in possessing an elongate and tubular external auditory meatus (Gaudin & Wible 2006). Some modern phylogenetic work still finds this result (Herrera et al. 2017).

Caption: a Pink fairy armadillo taxiderm specimen and mounted skeleton, both on display at the Grant Museum of Zoology, London. It should be obvious that there’s a whole lot of weird going on here. Just about everything in the skeleton is remarkable. Check out how the rounded shield at the rear looks fused to the pelvis, the strongly reduced tail and the giant foreclaws. As for the skull… I have no idea what’s going on with those two rounded bosses that look like horns. Rad. Images: Darren Naish.

There are two extant fairy armadillo species: the Pink fairy armadillo Chlamyphorus truncatus of central Argentina, and the Greater or Chacoan fairy armadillo Chaetophractus retusus of Bolivia, Paraguay and northern Argentina. The second species has sometimes been included in Chlamyphorus and the generic name Burmeisteria Gray, 1865 has also been used for it; the two extant species belong to lineages that  appear to have been separate since the Oligocene, so distinct generic status is appropriate (Delsuc et al. 2012). These animals are tiny, some adults of C. truncatus being only just over 8 cm in head and body length. They inhabit dry grasslands and sandy plains and are rapid burrowers that apparently use the subcircular armour plate covering the rear end as a shield or plug to block their burrow (Nowak 1999).

Caption: it turns out that the two fairy armadillo lineages are highly distinct, more so anatomically than most non-specialists realize (Greater or Chacoan fairy armadillo illustrations at right, from Hermann Burmeister’s description of the holotype). And molecular phylogenetics shows that they’ve been distinct for around 17 million years, as shown by the phylogeny (from Delsuc et al. 2012) at left. Images: Delsuc et al. 2012; public domain.

Indeed, they’ve converged on the ‘mole’ ecotype that evolved at least four times elsewhere within mammals (marsupial moles, golden moles, true moles, palaenodonts). They have reduced eyes, enlarged claws on their forelimbs, a silky pelt, a strongly reduced and mostly immobile tail, and a streamlined and flexible armour covering that includes the aforementioned posterior plate. Little is known of their ecology or behaviour for the obvious reason that they’re rarely seen alive. A lot more could be said about them but this will do for now. A few years ago, there was a non-serious effort to get them renamed ‘battle hamsters’ but it didn’t go anywhere… which is good, because it sure wouldn’t be helpful to have a group of xenarthans with the word ‘hamster’ in the name.

Remaining tolypeutine armadillos. Molecular studies find remaining tolypeutines to be a clade, with the remarkable Giant armadillo Priodontes maximus being the sister-taxon to the three-banded armadillos (Tolypeutes) and the naked-tailed armadillos (Cabassous). All three genera are united by some authors within Priodontini (Delsuc et al. 2003). Priodontes is a superstar armadillo, well known for its comparatively large size: it reaches 30 kg at least (note that all those mentions of specimens exceeding 60 kg are apparently based on overweight captive individuals). It’s also notable for its amazing hand claws and digging prowess, it probably being the most proficient and specialized digger among armadillos after the fairy armadillos (Vizcaino et al. 1999, Vizcaino & Milne 2002). The good news is that I’ve written about this species before (albeit at Tet Zoo ver 2): go here for that article.

Caption: this, obviously, is an illustration from a children’s book (specifically, Peter Spier’s 1971 Gobble Growl Grunt). I include it to emphasize the fact that the semi-bipedal tendencies and ‘claw-supported walking’ abilities of certain armadillos are widely known, and long have been, yet rarely mentioned outside of specialized literature. Image: (c) Peter Spier.

Three-banded armadillos are very special in being the only armadillos that can properly ‘enroll’ to form a sphere. The two species – Tolypeutes tricinctus of Brazil and the more widespread T. matacus – possess shell-like anterior and posterior carapacial segments that allow the limbs, head and tail to be tucked within. So effective, tight and rapid-action is this defence that they can even hop a short distance off the ground before snapping the shell shut before hitting the ground.

Like some other tolypeutines, their forelimb claws are so long and big relative to the rest of the hand that they’re ‘claw walkers’. Three-banded armadillos don’t excavate burrows but will use shelters constructed by other animals, like anteaters [UPDATE: see comments. It’s now know that they can dig their own burrows too]. They’re mostly denizens of grasslands and marshes; ants, termites and beetle larvae form most of their diet but they also eat fruit (Nowak 1999).

Caption: how, exactly, do three-banded armadillos enroll? It might be that their vertebral anatomy isn’t tremendously unusual relative to that of other xenarthrans but that the intricate, interlocking joints of the dermal skeleton are the key innovation here. Maybe I should have checked before writing this. This photo was taken at the Museum of Osteology, Oklahoma, USA. Image: Mathew Wedel, SV-POW!, original here.

Caption: three-banded armadillos are very unusual little animals. They’re partly cute, but also partly quite disturbing. Features to look for include the intricate sculpting of the scutes, the scaliness of the ears, and the massive length of the foreclaws. Images: T. tricinctus at left by ChrisStubbs, CC BY-SA 3.0 (original here); T. matacus at right by Hedwig Storch, CC BY-SA 3.0 (original here).

Finally, naked-tailed armadillos are among the most obscure armadillos of all. They superficially resemble Priodontes but are mostly 30-40 cm in head and body length (the tail adds an extra 9-20 cm) and generally weigh between 3 and 6 kg. They’re short-snouted, have relatively big ears, and possess 10-13 mobile bands across the middle of the body. As suggested by the common name, they’re unique in having a mostly unarmoured tail. It’s long and slender and decorated with a reduced number of small, widely spaced scales.

Naked-tailed armadillos – four extant species are recognized – are among the most generalized of armadillos, variously occurring in lowlands and uplands, grassland, and riverside woodland and marsh, and they’re good at burrowing and swimming as well as running. They appear to mostly rely on ants and termites.

Caption: there aren’t many good photos of naked-tailed armadillos in the wild. This is a Southern naked-tailed armadillo Cabassous unicinctus, a species that occurs across most of Brazil and in adjacent countries across northern continental South America. Image: Ben P, CC BY 4.0 (original here).

And that’s where we’ll end things. This is absolutely not a through look at fossil armadillos, since there are several fascinating taxa – interesting anatomically and in phylogenetic position – that I’ve deliberately ignored here. So, we have to come back to these animals in time. The main function of this article was to show how glyptodonts (and other big armadillos known only as fossils) fit within armadillo phylogeny and diversity as a whole. When we revisit these animals – which we will do, reasonably soon – it will be to discuss glyptodonts alone…

For previous Tet Zoo articles on armadillos and othr xenarthrans, see…

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