Paleontology Icon Paleontology

Fossil Friday: The Giant Armadillo Glyptodon and the Abrupt Origin of Xenarthrans

Günter Bechly
Photo: Gylptodon, by Wolfman SF via Wikimedia, GFDL and CC BY-SA 3.0.

This Fossil Friday we continue our series on the origins of the various modern placental mammal orders. Our subject today is the order Xenarthra, which is endemic to the New World and divided into two suborders, Cingulata (armadillos and their extinct relatives, pampatheres and glyptodonts) and Pilosa (sloths and anteaters). Both suborders include examples of the extinct Pleistocene megafauna of America. The suborder Pilosa includes the giant ground sloths like the genus Megatherium, and the suborder Cingulata includes the car-sized giant armadillos of the genus Glyptodon. A complete skeleton of Glyptodon asper from the Pleistocene of Argentina is featured at the top of this article. This specimen is on display at the Natural History Museum of Vienna. With an age of only 1.5 million years it is very far from being the oldest representative of this order. A recent review article by De Iuliis (2018) commented that:

These three clades and the differences between them reflect deep histories that reach back at least to the Paleocene and their fossil representation (of cingulates and sloths, but not vermilinguans) is exceptionally rich and diverse.

So, let’s have a closer look at this rich fossil record of xenarthrans. Gaudin & Croft (2015: fig. 2) provided an excellent chart of the stratigraphic distribution of the xenarthran fossil record with up-to-date chronology of the South American Land Mammal Ages (SALMA). They concluded that ”no unambiguous Paleocene fossil xenarthran remains are known.” So what are the oldest fossils of this order known to science?

Oldest Fossils of the Order

The more primitive suborder Cingulata is indeed well represented in the Paleogene fossil record from South America (Sedor et al. 2022). The earliest known cingulate and arguably oldest fossil representative of Xenarthra is Riostegotherium yanei described by Oliveira & Bergqvist (1998) from the Itaboraí Basin in the Rio de Janeiro State of Brazil. This material was already mentioned by Scillato-Yané (1976) under the incorrect name Prostegotherium. There is also at least one other undescribed armadillo-like species from this locality and age (Cifelli 1983Bergqvist et al. 20042019). A thorough revision of the material by Bergqvist et al. (2004) confirmed the identification of Riostegotherium as oldest xenarthran remains (also see Bergqvist et al. 2019).

Interestingly, Bergqvist et al. (2004) also observed that “shared similarities to palaeanodonts add support to the proposal that Palaeanodonta may have been ancestral to, or is the sister-taxon of Xenarthra”. Why is this interesting? Because the extinct Palaeanodonta a few years later turned out to be stem pangolins and both turned out to not be related to Xenarthra at all (e.g., Gaudin et al. 2009). This shows how the alleged connection between morphological similarity and phylogenetic relationship is rather a Darwinist myth that is upheld as convenient tool to promote the theory.

Anyway, there are also some problems with the dating of Riostegotherium: The deposits where it was found belong to the Itaboraian SALMA, which was was originally dated by Marshall (1985) to the middle Paleocene (63.6-61 mya), but this was indirectly inferred in the absence of radioisotopic or magnetostratigraphic datings. Bond et al. (1995) instead suggested a Paleocene/Eocene age of 60-57 mya, which was also accepted by Bergqvist et al. (20042019). Gelfo et al. (2009) provisionally re-dated the Itaboraian SALMA to an Early Eocene age of 55.5-53.5 mya (Lower Ypresian). The seminal work of Woodburne et al. (2014) moved the dating even a bit younger to the Middle Ypresian about 53-50 mya, contemporaneous with the Early Eocene Climatic Optimum (EECO). Similarly, Gaudin & Croft (2015) suggested an age of 54-52 mya in their stratigraphic chart. Nevertheless, Bergqvist et al. (2019) mentioned that “study in progress by the senior author challenges this latter interpretation, suggesting that at least part of the fissures was formed and filled during the late Paleocene.” Therefore they just gave a vague Paleocene/Eocene age. Apparently the study in progress is not yet published to this day. Therefore, it cannot yet be excluded that Riostegotherium might be of Late Paleocene age after all.

Prior to the discovery of Riostegotherium, the oldest xenarthrans were astegotheriine armadillos from the Barrancan subage of the Casamayoran SALMA of Argentina, which was believed to be about 7 million years younger (Scillato-Yané 1976). According to Kay et al. (1999) “the Casamayoran SALMA was at least 18–20 m.y. younger than previously assumed”. Therefore, Dunn et al. (2013) and Ciancio et al. (2016) dated the Barrancan to a Middle Eocene (Lutetian-Bartonian) age of 41.7-39.0 mya, which was basically confirmed by Woodburne et al. (2014) with an estimate of 42-38.5 mya (also see Gaudin & Croft 2015).

Remains of the astegotheriine armadillos Stegosimpsonia sp. and Astegotherium dichotomus were recovered from Cañadón Vaca in Patagonia. The respective layers date to the older Vacan subage (as opposed to the younger Barrancan subage) of the Casamayoran SALMA from the early Middle Eocene about 46-44 mya (Cifelli 1985Gaudin & Croft 2015Ciancio et al. 20182019).

The extinct armadillo taxa Peltephilidae and Astegotheriini are also known from the Riochican SALMA of Patagonia (Simpson 1948, McKenna & Bell 1997, Oliveira & Bergqvist 1998Gelfo et al. 2010). The Riochican SALMA is interspersed between the older Itaboraian SALMA and the younger Casamayoran SALMA. It had been dated to a Late Paleocene age of 57-55.5 mya by Bond et al. (1995), but was later re-dated to be only about 49-48.5 mya (Ypresian, Early Eocene) according to Woodburne et al. (2014), and to 51-49.5 by Gaudin & Croft (2015).

Armadillo remains of Pucatherium parvum and Noatherium emilioi have recently been described from the lower Lumbrera Formation in Northwestern Argentina (Fernicola et al. 2021), which the latter authors re-dated to the Early Eocene Climatic Optimum (Ypresian). This is older than previously believed, so that these armadillos could be contemporaneous with Riostegotherium if the re-dating of the Itaburaian by Woodburne et al. (2014) is correct (see above).

Considerable Scientific Controversy

Another recent discovery is a xenarthran metacarpal bone from the Late Eocene of Seymour Island in Antarctica (Davis et al. 2020). It was found in the Cucullaea I Allomember (TELM4) of the La Meseta Formation. The age of this formation is a matter of considerable scientific controversy, which I will discuss in great detail in a forthcoming technical paper on the waiting time problem in the origin of whales (Bechly et al. in prep.). Here it must be sufficient to note that an Early Eocene (Ypresian) age of 52-48 mya seems most likely and represents the consensus of most experts based on different lines of evidence (strontium isotopes, magnetostratigraphy, eustatic lowstands, dinoflagellate and mammalian biostratigraphy), while some dissenters are considering a younger Middle Eocene (Bartonian) age of about 40 mya mainly based on some dinoflagellate cysts.

The earliest fossil record for the suborder Pilosa is Pseudoglyptodon from the Priabonian-Bartonian (37.8 mya) of Argentina (Gaudin & Croft 2015). Within Pilosa there are two major subgroups: sloths (Folivora) and anteaters (Vermilingua). Ameghino (1895) described an astragalus of Proplatyarthrus longipes from the early Late Eocene (Mustersan SALMA), which could be the oldest folivoran, but unfortunately this specimen seems to be lost according to Pujos et al. (2021). The oldest other alleged sloth remains were from the Middle Eocene of Antarctica (Vizcaíano & Scillato-Yané 1995), but were disputed and considered to be an undetermined mammal by MacPhee & Reguero (2010)Pseudoglyptodon sallaensiswas described by Engelmann (1987), based on a mandible fragment from the Oligocene Salla Beds (Deseadan SALMA) of Bolivia, which also yielded other armadillo fossils (Billet et al. 2011). As already mentioned before, Pseudoglyptodon is commonly considered to be the oldest folivoran, but its possibly not a sloth in the strict sense (Pujos & De Iuliis 2007). Due to its peculiar characteristics and fragmentary preservation it remains enigmatic (Pujos & De Iuliis 2007Pujos et al. 2021). Engelmann (1987) gave an age of 25-28 mya, which agrees with modern datings of the Deseadan SALMA to 29.4-24.2 mya (Dunn et al. 2013). McKenna et al. (2006) described new material of Pseudoglyptodon from the Late Eocene-Early Oligocene (Tinguirirican SALMA, 33.6-31.3 mya, Dunn et al. 2013) of Chile and the Late Eocene of Cerro Blanco in Argentina (Mustersan SALMA), and recognized this genus as the sister group of all other sloths. Nevertheless, Varela et al. (2019) commented: “However, as Pseudoglyptodon presents many convergences with cingulates, we cannot rule out its position to be an artifact of our limited knowledge of this taxon.” The Mustersan SALMA was traditionally considered to be of Middle Eocene age, then considered to be postdating 35-36 mya (Kay et al. 1999); but ultimately recognized as early Late Eocene with an age estimates of 38.2-38 mya (Dunn et al. 2013), and 37.9-36.5 mya (Woodburne et al. 2014Gaudin & Croft 2015). Consequently, the Argentine material of Pseudoglyptodon indeed represents the oldest known fossil pilosans and likely the oldest sloths as well.

Some other very early fossil remains that are unequivocally referable to sloths are a Megalonychidae from the Early Oligocene (ca. 35 mya) of Puerto Rico (MacPhee & Iturralde Vinent 1995) and Patagonia (Carlini & Scillato-Yané_2004).

What About Anteaters?

The oldest fossil record of anteaters is an undescribed vermilinguan from the Early Miocene Colhuehuapian SALMA (20 mya) of Patagonia (Carlini et al. 1992, Gaudin & Branham 1998, Gaudin & Croft 2015). This implies a 30 million year ghost lineage of undocumented existence (Delsuc et al. 2001). The oldest described vermilinguan is Protamandua rothi from the Early to Middle Miocene Santacruzian of Patagonia (Ameghino 1904, Hirschfeld 1976Patterson et al. 1992Gaudin & Branham 1998). According to Gaudin & Croft (2015) it is about 18 million years old, but PaleoDB gives a range of 17.5-11.608 mya. We see that in most cases even the most modern radiometric methods provided quite different and fuzzy datings of the fossil outcrops. This does not mean that all the datings are completely wrong, but it shows that we should not place too much confidence in the current consensus concerning precise dates and possible evolutionary scenarios that are based upon them.

This also holds for so-called molecular clock datings, which place the origin of armadillos around the K/Pg boundary (Delsuc et al. 20012004Presslee et al. 2019). For Darwinists this would necessarily require an even earlier origin for the order Xernarthra in the Late Cretaceous. Too bad, this is of course strongly contradicted by the fossil record and the total absence of any Cretaceous crown group placental mammals. Should we dare to consider the possibility that something is wrong with the Darwinist assumptions? Heaven forbid!

An Abrupt Appearance

Anyway, we can conclude from the discussion above that the order Xenarthra appeared abruptly in the Lower Eocene about 53 million years ago, only 3 million years after the oldest fossils of our own order Primates, which we discussed last week. Carlini & Scillato-Yané (2004) made a revealing admission:

The absence of most major groups of Xenarthra in South American mammal-bearing sediments of Late Cretaceous and Early Paleocene age is the greatest enigma in the study of this Superorder.

I totally agree and can only note that this of course only emphasizes the abruptness of their appearance in the fossil record.

Xenarthra is one of the four major clades of placental mammals recognized in modern phylogenetic systematics. The three others are AfrotheriaEuarchontoglires, and Laurasiatheria. Next Fossil Friday we will look at a member of the African mammal clade Afrotheria, i.e., the aardvark order Tubulidentata and its fossil relatives.

P.S.: I have already discussed the misidentified alleged European anteater Eurotamandua from the Eocene Messel Pit in a previous Fossil Friday article (Bechly 2022).


  • Ameghino F 1895. Premiere contribution a la connaissance de la faune mammalogique des couches a PyrotheriumBoletín del Instituto Geográfico Argentino 15, 1–60.
  • Ameghino F 1904. Nuevas especies de mamíferos, cretáceos y terciarios de la República Argentina. Anales de la Sociedad Científica Argentina 56, 3–142.
  • Bechly G 2022. Fossil Friday: Eurotamandua — Anteater or Not Even Close? Evolution News October 14, 2022.
  • Bergqvist LP, Abrantes ÉAL & Avilla LdS 2004. The Xenarthra (Mammalia) of São José de Itaboraí Basin (upper Paleocene, Itaboraian), Río de Janeiro, Brazil. Geodiversitas 26(2), 323–337.
  • Bergqvist LP, Pereira PVLGdC, Machado AS, Castro MCD, Melki LB & Lopes RT 2019. Osteoderm microstructure of Riostegotherium yanei, the oldest Xenarthra. Anais Da Academia Brasileira de Ciências 91(Suppl. 2):e20181290, 1–21. DOI:
  • Billet G, Hautier L, de Muizon C & Valentin X 2011. Oldest cingulate skulls provide congruence between morphological and molecular scenarios of armadillo evolution. Proceedings of the Royal Society B 278(1719), 2791–2797. DOI:
  • Bond M, Carlini AA, Goin FJ, Legarreta L, Ortiz-Jaureguizar E, Pascual R & Uliana MA 1995. Episodes in South American land mammal evolution and sedimentation: testing their apparent concurrence in a Paleocene succession from central Patagonia. Actas VI Congreso Argentino de Paleontología y Bioestratigrafía, Trelew, Argentina, pp. 47–58.
  • Carlini AA & Scillato-Yané GJ 2004. The oldest Megalonychidae (Xenarthra: Tardigrada); Phylogenetic relationships and an emended diagnosis of the family.    Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen 233(3), 423–443 DOI:
  • Carlini AA, Scillato-Yané GJ, Vizcaíno SF & Dozo MT 1992. Un singular Myrmecophagidae (Xenarthra, Vermilingua) de Edad Colhuehuapense (Oligoceno Tardio-Mioceno Temprano) de Patagonia, Argentina. Ameghiniana 29, 176.
  • Ciancio MR, Herrera C, Aramayo A, Payrola P & Babot J 2016. Diversity of cingulate xenarthrans in the middle–late Eocene of Northwestern Argentina. Acta Palaeontologica Polonica 61(3), 575–590. DOI:
  • Ciancio MR, Salgado Ahumada JS & Carlini AA 2018. Los Dasypodidae (Mammalia, Xenarthra) del Eoceno medio (Edad Mamífero) Casamayorense de Patagonia. Reunión de Comunicaciones de la Asociación Paleontológica Argentina, Perto Madryn, 2018, p. 53. DOI:
  • Ciancio MR, Krmpotic CM, Scarano AC & Epele MB 2019. Internal Morphology of Osteoderms of Extinct Armadillos and Its Relationship with Environmental Conditions. Journal of Mammalian Evolution 26, 71–83. DOI:
  • Cifelli RL 1983. Eutherian tarsals from the late Paleocene of Brazil. American Museum Novitates 2761, 1–31.
  • Cifelli RL 1985. Biostratigraphy of the Casamayoran, Early Eocene, of Patagonia. American Museum Novitates 2820, 1–26.
  • Davis SN, Torres CR, Musser GM, Proffitt JV, Crouch NMA, Lundelius EL, Lamanna MC & Clarke JA 2020. New mammalian and avian records from the late Eocene La Meseta and Submeseta formations of Seymour Island, Antarctica. PeerJ 8:e8268, 1–27. DOI:
  • De Iuliis G 2018. Recent progress and future prospects in fossil xenarthran studies, with emphasis on current methodology in sloth taxonomy. Journal of Mammalian Evolution 25, 449–458. DOI:
  • Delsuc F, Catzeflis FM, Stanhope MJ & Douzery EJP 2001. The evolution of armadillos, anteaters and sloths depicted by nuclear and mitochondrial phylogenies: implications for the status of the enigmatic fossil EurotamanduaProceedings of the Royal Society B 268(1476), 1605–1615. DOI:
  • Delsuc F, Vizcaíno SF & Douzery EJP 2004. Influence of Tertiary paleoenvironmental changes on the diversification of South American mammals: a relaxed molecular clock study within xenarthrans. BMC Evolutionary Biology 4:11, 1–13. DOI:
  • Dunn ER, Madden RH, Kohn MJ, Schmitz MD, Strömberg CAE, Carlini AA, Ré GH & Crowley J 2013. A new chronology for middle Eocene–early Miocene South American Land Mammal Ages. GSA Bulletin 125(3-4), 539–555. DOI:
  • Engelmann GF 1987. A new Deseadan sloth (Mammalia: Xenarthra) from Salla, Bolivia, and its implications for the primitive condition of the dentition in Edentates. Journal of Vertebrate Paleontology 7(2), 217–223. DOI:
  • Fernicola JC, Zimicz AN, Chornogubsky L, Ducea M, Cruz LE, Bond M, Arnal M, Cárdenas M & Fernández M 2021. The Early Eocene Climatic Optimum at the Lower Section of the Lumbrera Formation (Ypresian, Salta Province, Northwestern Argentina): Origin and Early Diversification of the Cingulata. Journal of Mammalian Evolution 28(3), 621–633. DOI:
  • Gaudin TJ & Branham DG 1998. The phylogeny of the Myrmecophagidae (Mammalia, Xenarthra, Vermilingua) and relationship of Eurotamandua to the Vermilingua. Journal of Mammalian Evolution 5(3), 237–265. DOI:
  • Gaudin TJ & Croft DA 2015. Paleogene Xenarthra and the evolution of South American mammals. Journal of Mammalogy 96(4), 622–634. DOI:
  • Gaudin TJ, Emry RJ & Wible JR 2009. The Phylogeny of Living and Extinct Pangolins (Mammalia, Pholidota) and Associated Taxa: A Morphology Based Analysis. Journal of Mammalian Evolution 16(4), 235–305. DOI:
  • Gelfo JN, Goin FJ, Woodburne MA & Muizon C DE 2009. Biochronological relationships of the earliest South American Paleogene mammalian faunas. Palaeontology 52(1), 251–269. DOI:
  • Gelfo JN, Chornogbusky L, López GM, Goin FJ & Ciancio MR 2010. Biochronological relationships of the mammal fauna from the Paleogene of Las Violetas, Chubut Province, Argentina. p. 61 in: Ballent S, Artabe A & Tortello F (eds.). Abstracts of X Congreso Argentino de Paleontología y Bioestratigrafía y VII Congreso Latinoamericano de Paleontología. Universidad Nacional de La Plata, Buenos Aires.
  • Hirschfeld SE 1976. A New Fossil Anteater (Edentata, Mammalia) from Colombia, S.A. and Evolution of the Vermilingua. Journal of Paleontology 50(3), 419–432.
  • Kay RF, Madden RH, Vucetich MG, Carlini AA, Mazzoni MM, Ré GH, Heizler M & Sandeman H 1999. Revised geochronology of the Casamayoran South American Land Mammal Age: Climatic and biotic implications. PNAS 96(23), 13235–13240. DOI:
  • MacPhee RD & Iturralde-Vinent MA 1995. Origin of the Greater Antillean land mammal fauna, 1: new Tertiary fossils from Cuba and Puerto Rico. American Museum Novitates 3141, 1–31.
  • MacPhee RDE & Reguero MA 2010. Reinterpretation of a Middle Eocene Record of Tardigrada (Pilosa, Xenarthra, Mammalia) from La Meseta Formation, Seymour Island, West Antarctica. American Museum Novitates 3689, 1–21. DOI:
  • Marshall LG 1985. Geochronology and Land-Mammal Biochronology of the Transamerican Faunal Interchange. p p. 49–85 in: Stehli FG & Webb SD (eds). The Great American Biotic Interchange. Topics in Geobiology vol 4. Springer, New York (NY), xvii+532 pp. DOI:
  • McKenna MC & Bell SK 1997. Classification of mammals above the species level. Colombia University Press, New York, 631 pp.
  • McKenna MC, Wyss AR & Flynn LL 2006. Paleogene pseudoglyptodont xenarthrans from central Chile and Argentine Patagonia. American Museum Novitates 3536, 1–18.
  • Oliveira ÉV & Bergqvist LP 1998. A new Paleocene armadillo (Mammalia, Dasypodoidea) from the Itaboraí Basin, Brazil. pp. 35–40 in: Casadío S (ed.). Paleógeno de América del Sur y de la Península Antártica. Asociación Paleontológica Argentina, Publicación Especial 5.
  • Patterson B, Segall W, Turnbull WD & Gaudin TJ 1992. The ear region in xenarthrans (= Edentata, Mammalia). Part II. Pilosa (sloths, anteaters), palaeanodonts, and a miscellany. Fieldiana Geology ns 24, 1–79. DOI:
  • Presslee S, Slater GJ, Pujos F et al. 2019. Palaeoproteomics resolves sloth relationships. Nature Ecology & Evolution 3(7), 1121–1130. DOI:
  • Pujos F & De Iuliis G 2007. Late Oligocene Megatherioidea Fauna (Mammalia: Xenarthra) from Salla-Luribay (Bolivia): new data on basal sloth radiation and Cingulata-Phyllophaga split. Journal of Vertebrate Paleontology 27(1), 132–144. DOI:[132:LOMFMX]2.0.CO;2
  • Pujos F, Ciancio MR, Forasiepi AM, Pujos M, Candela AM, Vera B, Reguero MA, Combina AM & Cerdeño E 2021. The late Oligocene xenarthran fauna of Quebrada Fiera (Mendoza, Argentina) and its implications for sloth origins and the diversity of Palaeogene cingulates. Papers in Palaeontology 7(3), 1613–1656. DOI:
  • Scillato-Yané GJ 1976. Sobre un Dasypodidae (Mammalia, Xenarthra) de Edad Riochiquense (Paleoceno superior) de Itaboraí (Brasil). Anais Academia Brasileira de Ciências 48, 527–530.
  • Sedor FA, Klimeck TBF, Dias EV, Oliveira EV, Ciancio MR, Vieira KTP, Fernandes LA & Angulo RJ 2022. The Eocene armadillo Utaetus buccatus (Euphractinae) in the Guabirotuba Formation (Curitiba Basin) and carapace morphological implications. Journal of South American Earth Sciences 114:103694. DOI:
  • Simpson GG 1948. The beginning of the age of mammals in South America. Part 1. Introduction. Systematics: Marsupialia, Edentata, Condylarthra, Litopterna, and Notioprogonia. Bulletin of the American Museum of Natural History 91, 1–232.
  • Varela L, Tambusso PS, McDonald HG & Farina RA 2019. Phylogeny, macroevolutionary trends and historical biogeography of sloths: insights from a Bayesian morphological clock analysis. Systematic Biology 68(2), 204–218. DOI:
  • Vizcaíano SF & Scillato-Yané GJ 1995. An Eocene tardigrade (Mammalia, Xenarthra) from Seymour Island, West Antarctica. Antarctic Science 7(4), 407–408. DOI:
  • Woodburne MO, Goin FJ, Raigemborn MS, Heizler M, Gelfo JN & Oliveira EV 2014. Revised timing of the South American early Paleogene land mammal ages. Journal of South American Earth Sciences 54, 109–119. DOI: