Red: anteater, yellow: armadillo, blue: sloth, orange: both anteater and armadillo, green: both armadillo and sloth, purple: anteater, armadillo and sloth
Xenarthrans share several characteristics that are not present in other placental mammals, which suggest that Xenarthrans descend from subterranean diggers. The name Xenarthra derives from the two ancient Greek words ξένος (xénos), meaning "strange, unusual", and ἄρθρον (árthron), meaning "joint",[4][5] and refers to their vertebral joints, which have extra articulations that are unlike other mammals. The ischium of the pelvis is also fused to the sacrum of the spine.[6] Xenarthran limb bones are typically robust, with large processes for muscle attachment. Relative to their body size, living xenarthrans are extremely strong.[7] Their limb bone structures are unusual. They have single-color vision. The teeth of Xenarthrans are unique. Xenarthrans are also often considered to be among the most primitive of placental mammals. Females show no clear distinction between the uterus and vagina, and males have testicles inside the body, which are located between the bladder and the rectum.[8] Xenarthrans have the lowest metabolic rates among therians.[9][10]
Xenarthran forms and lifestyles include:
Armadillos: Mostly small and some larger omnivores and insectivores with flexible banded body armor
Glyptodonts: Large herbivores with a rigid semi-spherical carapace
Pampatheres: Large herbivores (and possibly omnivores) with banded body armor
Anteaters: Small to large specialized feeders on social insects
Tree sloths: Medium-sized folivores specialized for life hanging upside-down in trees
Ground sloths: Medium to very large ground-living herbivores (and possibly omnivores)
Aquatic sloths: Thalassocnus, a medium-sized herbivore, is the only known aquatic sloth
^Vizcaíno, Sergio F.; Loughry, W. J., eds. (2008). The biology of the Xenarthra. Gainesville: University Press of Florida. ISBN978-0-8130-3718-9. OCLC741613153.
^Webb, S. David (2001). "Chapter 10: Mammalia 2: Xenarthrans". In Hulbert, Richard C. (ed.). The Fossil Vertebrates of Florida. University Press of Florida. p. 176. ISBN0-8130-1822-6.
^Kleisner, K; Ivell, R; Flegr, J (2010). "The evolutionary history of testicular externalization and the origin of the scrotum". Journal of Biosciences. 35 (1): 27–37. doi:10.1007/s12038-010-0005-7. PMID20413907. S2CID11962872.