Tetrapod Zoology

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Regular visitors will no doubt have noticed the failure of my promise to post a picture a day. Well, alas, I’m going to have to take a much more relaxed approach, as it has proved impossible to find time even for that. So, I might post a new picture every day on the blog, and I might not. My weekend was taken up with various social events, and since then there just hasn’t been the time to add new stuff… other than the sheep article of course. And what about my promise to, err, stick only to the things I’ve nearly finished writing but have yet to complete? Well, stuff that too. Today, continuing the theme initiated with Ten things you didn’t know about sloths, we’re going to embark on a quick tour of the fascinating, no-holds-barred, pedal-to-the-metal world of THE ARMADILLOS, concentrating in particular on some of the more remarkable fossil forms …although my original plan to write ten things about armadillos got whittled down to five for the usual reasons of space and time…

Armadillos are xenarthrans: part of the same clade of placental mammals as sloths and anteaters. They are, of course, best known for their armour. It is composed of interlocking polygonal dermal ossifications (termed scutes, ossicles or osteoderms) that form continuous pectoral and pelvic bucklers, separated in the middle by flexible bands (numbering from three to 13 depending on the species) formed by rectangular osteoderms. The bands allow the animal to twist and bend and, in some species, to roll into a ball for protection. Armadillos are supreme generalists and occur from rainforests to deserts, and everything in between. They are predominantly insectivorous, and some are specialised myrmecophages (ant- and/or termite-eaters). Others are omnivores. Powerful limbs equipped with large curved claws allow them to be good diggers and burrowers, and the fairy armadillos or pichiciegos Chlamyphorus [pictured above] are mole-like fossorial forms. The word armadillo means ‘little armoured one’ (not ‘little tank’ as I’ve read in a few places).

There are about 25 living armadillo species, so they are quite a speciose group. However, their diversity was greater in the past and we know of several armadillo clades, as well as many, many species, that are now entirely extinct. In fact a 1980 catalogue listed over 100 fossil species of armadillo. So, here we go… (oh, and, no offence intended to the informed readers to whom these things will not be ‘things you didn’t know’)…

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1. The biggest living armadillo is the Giant armadillo Priodontes maximus [shown in adjacent image: pic from here]. It can reach 1.5 m in total length and may weigh over 50 kg. This is huge. But it’s not so huge when we compare it with the biggest armadillos ever, the giant armadillos or pampatheres. Properly called pampatheriids (formerly chlamydotheriids), giant armadillos are best known from the Miocene and were still alive late in the Pleistocene (they may even have survived into the early Holocene in Brazil). Giant armadillos participated in the Great American Biotic Interchange and were present in North America during the Pliocene and Pleistocene. The biggest giant armadillo was Holmesina, a rhino-sized animal about 2 m long, 1 m tall at the shoulders, and with a skull about 30 cm long. I’ve been unable to find a precise mass estimate in the literature, but it would have weighed several hundred kg at least. How did these armadillos live? We’ll come back to that in a minute. Incidentally, the giant armadillo Pampatherium was one of the first fossil mammals to ever be described from South America, having been named in 1839… though back then it was known as Chlamytherium… which was a mistake and was changed in 1841 to Chlamydotherium… which proved to be preoccupied, hence the change in 1891 to Pampatherium. Incidentally, we are not talking about the glyptodonts: while armadillo-like, they are not true armadillos. But then, neither are pampatheres actually (read on).

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2. The Nine-banded armadillo Dasypus novemcinctus is slowly (or rapidly, take your pick) taking over the United States. Reported from Texas during the 1850s, by the 1920s it had spread to Louisiana. It got into Mississippi, Alabama and Oklahoma during the 1930s and during the 1940s expanded into Arkansas, Missouri and Kansas. By the 1970s it had been reported from Georgia, Tennessee, South Carolina, Colorado and Nebraska. The species has been present in Florida since an introduction made during WWI, and another in 1924. By the 1950s the animals were reportedly common throughout the state [map showing spread of armadillos borrowed from here]. Given their obligate production of quadruplets (read on), excellent swimming ability, general fearlessness and robust constitution, and ability to eat anything and thrive in diverse habitats, they are excellent colonists and would be difficult to eradicate (should anyone try). They may be bad news for ground-nesting birds. Besides humans, the Nine-banded armadillo is apparently the only mammal that carries leprosy, but this is apparently a good thing as they have been utilised in medical research. Why this species has spread so far so quickly is not entirely clear. Possibilities include the spread of poor-quality, predator-free habitat and progressive climatic amelioration (McBee & Baker 1982). Given that an extinct species of Dasypus, D. bellus, occurred across most of the same area during the Pleistocene, one might argue that armadillos are actually meant to be where they are now, and are merely reclaiming the area after a temporary absence.

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3. The Nine-banded armadillo is, clearly, the best known and most studied armadillo, but it is only one of six extant long-nosed armadillo (Dasypus) species. All long-nosed armadillos are particularly interesting from the point of view of reproductive biology in that they exhibit obligate polyembryony: females produce a single fertilized egg that then divides into four embryos, all of which are (of course) genetically identical. While suspected as early as 1909, obligate polyembryony was not really confirmed until the 1990s (Prodöhl et al. 1996, Loughry et al. 1998). Long-nosed armadillos are the only vertebrates that exhibit polyembryony every time they reproduce. They also delay implantation of embryos, with the 5 months between June/July and November/December being the usual period. However, exceptional cases are on record where implantation has been delayed for an amazing three years (although I’m sure I recall reading of a much longer delay somewhere – more like 12 years, though I can no longer locate this in the literature!).

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4. Several groups of fossil armadillos, including giant armadillos and eutatines, appear to have been specialised herbivores. Actually, whether giant armadillos and eutatines are really armadillos or not is a subject of minor debate, as some experts have argued that – within the armoured xenarthran clade Cingulata – both are more closely related to glyptodonts than to armadillos. Anyway, jaw and tooth morphology shows that giant armadillos were grazing herbivores: the palaeoenvironments and cranial morphology of the different species indicate that some ate fibrous plants growing in dry habitats, while others ate softer vegetation in wetter habitats (De Iuliis et al. 2000, Scillato-Yané et al. 2005, Vizcaíno et al. 1998) [adjacent image shows skull of giant armadillo Holmesina]. Eutatines, best known from the Oligocene, Miocene and Pliocene of Argentina, were shown by Vizcaíno & Bargo (1998) to exhibit jaw and tooth morphology, and a reconstructed muscular anatomy, strongly indicating a herbivorous diet consisting of leaves, buds and perhaps grasses. Perhaps most bizarrely, the absence of anterior incisiform teeth and of any evidence for a flexible snout or lips led these authors to suggest that Eutatus, the largest eutatine (it was about equal in size to the living Giant armadillo), may have used a long and flexible tongue as a food-gathering organ.

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5. While some living armadillos are omnivores and incorporate quite a lot of vertebrate prey in their diet (as much as 30% of the summer diet of Chaetophractus is made up of small vertebrates), none of the living species are dedicated carnivores. It used to be thought that the peltephilines of Eocene, Oligocene and Miocene Argentina and Bolivia were cursorial carnivores or scavengers, although the reasons for this were always shockingly poor. These highly unusual armadillos are notable for their short, wide snout, enlarged, tall cranium and horns [skull of Peltephilus shown in adjacent image]. Yes, horns (making them convergently similar to mylagaulid rodents). A recent reanalysis showed that peltephilines are likely to have been fossorial animals, eating tubers and other hard subterranean vegetation (Vizcaíno & Fariña 1997). The good news however is that at least one extinct armadillo really was a horrible rapacious predator: Vizcaíno & De Iuliis (2003) showed that Macroeuphractus from Miocene and Pliocene Argentina and Bolivia, well known for its large size (c. 100 kg) and big, conical caniniform teeth, was well suited for carnivory. Given that Macroeuphractus was a euphractine – a close relative of the living Chaetophractus, Euphractus and Zaedyus – its carnivorous habits can perhaps be regarded as ‘an extreme position in the carnivorous-omnivorous feeding behaviour of euphractines’ (Vizcaíno & De Iuliis 2003, p. 123). In other words, it perhaps wasn’t so exceptional among the group. But its large size meant that it could do things that other euphractines couldn’t, or can’t. A fairly horrific reconstruction of a hungry toothy Macroeuphractus tunnelling its way into the den of a group of happy little cute hare-like rodents decorates p. 135 of Vizcaíno and De Iuliis’ paper.

And on that, I say goodbye.

PS – happy Gigantoraptor day! If I had the time I would definitely write a post about it. An oviraptorosaur the size of a tyrannosaur. Swoon.

Refs – -

De Iuliis, G., Bargo, M. S. & Vizcaíno, S. F. 2000. Variation in skull morphology and mastication in the fossil giant armadillos Pampatherium spp. and allied genera (Mammalia: Xenarthra: Pampatheriidae), with comments on the systematics and distribution. Journal of Vertebrate Paleontology 20, 743-754.

Loughry, W. J., Prodöhl, P. A., McDonough, C. M. & Avise, J. C. 1998. Polyembryony in armadillos. American Scientist 86, 274-279.

McBee, K. & Baker, R. J. 1982. Dasypus novemcinctus. Mammalian Species 162, 1-9.

Prodöhl, P. A., Loughry, W. J., McDonough, C. M., Nelson, W. S. & Avise, J. C. 1996. Molecular documentation of polyembryony and the micro-spatial dispersion of clonal sibships in the nine- banded armadillo, Dasypus novemcinctus. Proceedings of the Royal Society of London B 263, 1643-1649.

Redford, K. H. & Wetzel, R. M. 1985. Euphractus sexcinctus. Mammalian Species 252, 1-4.

Scillato-Yané, G. J., Carlini, A. A., Tonni, E. P. & Noriega, J. I. 2005. Paleobiogeography of the late Pleistocene pampatheres of South America. Journal of South American Earth Sciences 20, 131-138.

Vizcaíno S.F. & Bargo, M. S. 1998. The masticatory apparatus of the armadillo Eutatus (Mammalia, Cingulata) and some allied genera: paleobiology and evolution. Paleobiology 24, 371-383.

- . & De Iuliis, G. 2003. Evidence for advanced carnivory in fossil armadillos (Mammalia: Xenarthra: Dasypodidae). Paleobiology 29, 123-138.

- ., De Iuliis G. & Bargo M.S. 1998. Skull shape, masticatory apparatus, and diet of Vassallia and Holmesina (Mammalia: Xenarthra: Pampatheriidae): when anatomy constrains destiny. Journal of Mammalian Evolution 5, 291-322.

- . & Fariña, R. A. 1997. Diet and locomotion of the armadillo Peltephilus: a new view. Lethaia 30, 79-86.

Comments

  1. #1 JW Tan
    June 13, 2007

    I seem to recall that fairy armadillos were once upon a time popular pets in the US. But I cannot confirm this even with a cursory Google search. Can anyone shed any light?

    They certainly have a high enough cute factor.

  2. #2 JW Tan
    June 13, 2007

    Another question – why are glyptodonts not true armadillos then? I think the NHM (in London) labels the glyptodont fossil in the main hall as an armadillo…

  3. #3 Sordes
    June 13, 2007

    Cool stuff (although I actually knew several of the points…), this creatures are nearly rivaling sloths in bizarrity. I made a rough estimation for the weight of Holmesina, based on a 33cm long skull compared with those of 19cm from a living giant armadillo, both from Scullsunlimited. I suppose both had a similar anatomy, even if Holmesina was probably like many other large animals a bit bulkier. I came to a weight of about 260kg, when I used the 50kg for a giant armadillo as base. I don´t know if a giant armadillo with a 19cm long skull weighs already 50kg, but I suppose a weight between 200 and 300kg seems probable for Holmesina.

  4. #4 coturnix
    June 13, 2007

    #6 – Armadillo is the model animal for the study of the structure, biomechanics and evolution of the mammalian penis. PZ has described some of that work, and the researcher, Diane Kelly, is a prolific and excellent blogger as well.

  5. #5 Ed Yong
    June 13, 2007

    6. Oi loike armadillos! Crunchy on the outside, chewy on the inside – armadillos!

    (This will be entirely lost on anyone who wasn’t in Britain in the mid-90s – to such people, I assure you I am not insane).

  6. #6 Hai~Ren
    June 13, 2007

    I do find it odd that for all the reconstructions of glyptodonts out there, I have yet to see one of a pampathere.

    Oh, and nothing about Eocursor? Bah, theropods get all the attention…… =P

  7. #7 Zac
    June 13, 2007

    Weird Southern U.S. Fact: in some state fairs people can participate in armadillo races. The armadillos run to a pile of manure that contains worms.

  8. #8 Diego
    June 13, 2007

    As a Floridian, born and bred, I appreciate these silly little critters. Armadillos are quite fascinating.

  9. #9 Nick Gardner
    June 13, 2007

    Delightful post on armadillos, my meager knowledge of them has gained a little from it. However, shameful to make mention of _Gigantoraptor_ and ignore the more infinitely important new ornithischian described by Butler et al. Silly theropods. ;)

  10. #10 Cameron
    June 13, 2007

    The Macmillan Illustrated Encyclopedia of Dinosaurs and Perhistoric Animals oddly (to me) portrayed Peltephilus as a 20 foot/6 meter long monsterous fairy armadillo-like critter. I found a small version of their illustration here:

    http://www.dcpaleo.org/Research/SAMammals/SAMammalsFrontXenarthra.gif

    As I have not heard anything about this armadillo getting up to Megatherium-level sizes, would I be correct in assuming something’s a bit wrong here?

    I’ve heard that those nine-banded invaders recently crossed the Ohio/Missouri River (apparently a considerable barrier) and have now invaded my native-ish Illinois. These instances of wildly expanding animal ranges really are quite fascinating…to me.

  11. #11 Noni Mausa
    June 13, 2007

    I believe Sanderson mentioned the fairy armadillos in an early book, stating they could dig faster than a man with a shovel trying to dig them up.

    As far as them ever being pets,I never heard mention of that. Yes, they are small and fluffy and somewhat pink, but on the other hand they are insectivores and therefore probably quite toothy (as are hedgehogs and shrews) and therefore maybe not something you would like to cuddle.

    Noni

  12. #12 Warren Beattie
    June 14, 2007

    P.A. Prodöhl? If it’s the same guy, he was one of my genetics lecturers in Belfast. I knew about armadillo polyembrony, but I didn’t know he was involved in its confirmation. Neat.

    And please stop telling us about (relatively) obscure extinct mammals. It’s pulling too much of my interest away from dinosaurs. Thankyoo.

  13. #13 Alan Kellogg
    June 14, 2007

    Noni Maura,

    Hedgehogs are really rather cool and calm little beasts. Once they learn to trust you (and you, them) they can be handled quite readily.

    There was an occasion on Late Night With David Letterman when Jack Hannah brought out a pair of rare hedgehogs. The two men talked about the animals, and while they did so the pair proceeded to mate right on Dave’s desk. A behavior in that particular species that had never been witnessed in captivity before. When an animal is that relaxed in the presence of humans…

  14. #14 Alan Kellogg
    June 14, 2007

    Oops. Just remembered, it was a pair of rare armadillos that had nookie on David Letterman’s desk. Still, both armadilloes and hedgehogs are placid little beasts once they get to know you. Long as you don’t act predatory they don’t see you as a predator.

  15. #15 johannes
    June 14, 2007

    > The Macmillan Illustrated Encyclopedia of Dinosaurs and Prehistoric
    > Animals oddly (to me) portrayed Peltephilus as a 20 foot/6 meter
    > long monsterous fairy armadillo-like critter.

    So the english edition had this too? I have always thought that this was just a misspelling in the german edition. It is actually a pity that such faults appear in an – otherwise quite good – book aimed principally at laypersons and children, wich is in most cases the only reference available to an average reader, who has no other sources to compare it to and takes the truth of its content for granted. The Macmillan Encyclopedia was (and is) quite popular and is in many cases the only book on extinct animals in a household. I wonder how many children grew up in the certain knowledge that there once was a gigantic, horned, predatory armadillo in South America?

  16. #16 Greg Popwell
    June 14, 2007

    Having been born and raised in central Alabama I can attest to the migration/invasion of the 9 banded armadillo. Don’t recall seeing them as a kid but now they are everywhere. They rival the Virginia opossum in the large number of roadkills.

  17. #17 Noni Mausa
    June 14, 2007

    Thanks, Alan, for your firsthand info about hedgehogs. The only ones I have met are other people’s pets, and they seemed quite reserved (probably because I am used to labrador retrievers — not reserved by anyone’s standards.)

    Speaking of animals moving north — in the past 10 to 15 years we have had possums showing up in Minnesota, when as kids in the 60s we always thought of them as animals of the deep south, persimmon country. Pesky beasts, getting into our garbage.

    I found a jettisoned baby one summer, still hairless and eyeless, and managed to double his size on an eyedropper before he died overnight in his shoebox. I’ve often wondered what I would have done if he had lived. Maybe I would have found him as charming as a hedgehog?

    Noni

  18. #18 Alexander Vargas
    June 14, 2007

    interesting about the horned aramadillos and rodents… I remember an article on the developmnt of atavism by brian hall wer ehe mentions that evrry now and then, rabbits are born with 6 or 7 rather large horns on their head… he even cites a peper looking that up
    C’mon Darrren, don’t disappoint me, you MUST know something more than I about that!!!
    I’ve never been sure that is true but those extinct horned rodents…

  19. #19 Alan Kellogg
    June 15, 2007

    Nomi,

    Keep in mind that the Virginia Opossum is a stupid beast. And it’s not the cute stupidity of the Tasmanian Devil, it is a mean stupidity.

    When it comes to keeping a wild animal as a pet, don’t. If you must, learn how to behave as a true superior. Don’t challenge, assert. A true superior doesn’t need to keep pushing those lower ranked. That causes resentment and leads to the impression that one can be challenged and challenged profitably. Interact, socialize with the animal and let it participate in your life. And support your pet when your kids abuse it.

    BTW, there is no such thing as a domestic rat. All pet rats are wild animals, it’s just that the rat (all species) is such a placid animal outside of a stressful situation that they not only tolerate handling, they actually come to anticipate it and to solicit the contact. Not only that, but rats love to be tickled.

    Which raises a question. As anybody tried tickling another animals? Besides rats, and the great apes that is.

  20. #20 Anthony Docimo
    June 15, 2007

    Mr. Naish: Post what you want, when you want to. We’re just glad you’re talking to us all.

  21. #21 TheBrummell
    June 15, 2007

    Weird Southern U.S. Fact: in some state fairs people can participate in armadillo races. The armadillos run to a pile of manure that contains worms.

    By participate, do you mean some humans attempt to outrun the armadillos on the way to the dungpile and the tasty, tasty worms? I’m pretty sure I could take the little buggers, no problem.

  22. #22 QrazyQat
    June 15, 2007

    Speaking of animals moving north — in the past 10 to 15 years we have had possums showing up in Minnesota, when as kids in the 60s we always thought of them as animals of the deep south, persimmon country.

    I lived in SE Minnesota as a kid (Rochester, Olmsted county) and we had possums there at that time. (late 50s/early 60s).

    In northern Arkansas (middle of the state right up by the Missouri border), where we went for vacation for many years, possums have turned up in the past 20 years and are commonly killed on the roads. I wonder about one thing; when I was a kid there we saw green anoles, which I see listed as being found only in the southern part of the state. But as an adult I never see an anole up there, just collared lizards. Difference in climate? More people, fewer anoles? Related in some way (same cause) as the armadillo expansion? Coincidence?

  23. #23 David Marjanovi?
    June 16, 2007

    Not only that, but rats love to be tickled.

    Not only that! When tickled, they laugh.

    It’s just ultrasound, so nobody noticed till a few years ago.

  24. #24 John Scanlon
    June 18, 2007

    I wondered if it was the same book on my shelf, and checked: in Australia it was the Collins Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. Peltephilus is illustrated as a horned fairy armadillo on p. 207 (’20 ft/6 m long’ on 209).

  25. #25 Darren Naish
    June 18, 2007

    It’s the same in the British edition too: life restoration on p. 207 and 6 m length given on p. 209. Alas poor Steve Holden (the artist): he evidently wasn’t given any useful source material. Bit surprised to see Savage making an error of this magnitude (he wrote the mammal text in the volume).

  26. #26 P Terry Hunt
    June 18, 2007

    In my experience, both 1st-hand as a former science textbook Desk Editor for a well-known Publisher (clue: ‘On the Origin of Species . . .’ was one of theirs), and 2nd-hand from the testimony of other writers (e.g. David Langford), it’s not uncommon for at least some if not all of a book’s illustrations and their captions to be sourced and written, sometimes at the last minute (production-wise), by publishing staff rather than the main writer(s), and without the latter’s approval or knowledge.

    Possibly the desk or production editor of this Macmillan / Collins volume, having failed to find (and/or obtain repro rights for) a really authentic illo of said beastie, filled the hole in his/her page proof at the last minute with whatever came to hand that wasn’t glaringly inappropriate. Without having the inside dope, it would be presumptious to blame Messrs Savage or Holden.

    On a general note: keep them coming, Darren! Hope to see you in Woolfardisworthy in August, if not before.

  27. #27 Bob Jase
    June 18, 2007

    Re: possums as southerners

    That’s what they were considered fifty-odd years ago when I was a kid growing up here in Connecticut. It was a rare thing to see one back in the late sixties, now they’re almost as common as feral cats even in the cities.

    Re: possums as mean stupid

    I disagree. They LOOK mean but I’ve never had any problems handling wild ones, I don’t even bother with wearing gloves. Note that I don’t dispute the stupid part.

    Re: rats

    Great pets! Get just one so you’re their only social contact and they’re (usually) friendly and playful although males aren’t as active as females.

    re: armadillos

    Yes, they’re the subject of the blog but unfortunately I’ve never had the chance to handle one or even see a live one.

  28. #28 Tommy Tyrberg
    June 19, 2007

    As for that crunchy/chewy bit armadillo meat is not bad. I ate some in Venezuela once and it was quite OK.

  29. #29 Dr Vector
    June 20, 2007

    do you mean some humans attempt to outrun the armadillos on the way to the dungpile and the tasty, tasty worms? I’m pretty sure I could take the little buggers, no problem.

    :-) I’d pay money to see that. Right up there with Gran’ma Ben and the Great Cow Race.

    However, my money would be on the armadillos. When I was growing up in rural Oklahoma those things would occasionally come along and tear up our yards. You could go to sleep with a pristine lawn and wake up with the Ho Chi Minh Trail. One time some neighbors who lived about a mile away called. A big armadillo had torn a hole in their flower bed and was doing his darnedest to dig under their front porch. Dad and I went over to see what we could do. While Dad tried to convince our elderly neighbor not to load his shotgun while it was pointed at people, I tried pulling the armadillo out by the tail. That was an exercise in complete futility. If either of us was moving the other, he was dragging me.

    Eventually the armadillo must have intuited the level of adversity he was facing, and he backed out of the hole and took off across the yard. I had been mentally preparing for that move. I was going to jump on him and try to catch him. I didn’t really have a plan for what I’d do with him after, but I caught a lot of stuff that way when I was a kid. But it didn’t really matter, because the armadillo just sort of vanished. Rarely in my life have I seen an animal move so fast. I think a fast dog could probably have kept up, but not a cat and certainly not a human.

    I have heard that the northward expansion of the nine-banded armadillo in the US has been facilitated by the ubiquitous metal culverts that you find in farm country, which give the armadillos someplace to shelter during cold weather. Anybody know anything about that?

  30. #30 Monado, FCD
    March 20, 2010

    I once read that the relatively hairless (nine-banded?) armadillos will burrow info, and under, a cow carcase and happily live with its food until it runs out of edible bits. Has anyone else heard of that?