Superorder Xenarthra

Composed of orders Cingulata and Pilosa

Distribution - Neotropics (and Cingulata invading N. America)

Position in the Eutherian phylogenetic tree (Murphy et al. 2001)

  1. General characteristics of these orders

    1. A tendency towards rigidity of the spine

      1. Xenarthran processes on vertebrae (especially lumbar)
      2. Fusion of vertebrae with pelvic girdle
      3. Fusion of cervical vertebrae

    2. Were once very diverse; some interesting ones:

      1. glyptodonts: had turtle-like shell; most completely armored of all vertebrates
        fossil skeleton
        artist's rendering
      2. Megalonyx : giant ground sloth
        fossil skeleton
        museum reconstruction
        artist's rendering
  1. Order Cingulata

    1. Characteristics
      1. Carapace
        • covers most of the body
        • made of dermal bone plates covered by epidermal scales
        • varies from a complete protective covering when animals roll into a ball, to a more loose fitting one that doesn't completely cover
        • attached to axial skeleton by muscles and ligaments (not in direct contact with the skeleton)
      2. Sparse hair
      3. Teeth
        • Lack incisors and canines
        • Teeth are cylindrical and rootless
      4. Most are terrestrial, some fossorial
      5. Well equipped for digging
      6. Eat insects and insect larvae, with occasional plant material, eggs, berries, etc.
    2. Family Dasypodidae (armadillos) - 8 genera, 20 species


  2. Order Pilosa
    1. General characteristics of Families Bradypodidae and Megalonichidae (sloths)
      1. Arboreal (have great difficulty moving on the ground) video
      2. Often move upside-down on the underside of branches
      3. Long-limbed, with forelimbs longer than hind
      4. Toes are fused ( syndactyly )
      5. Cervical vertebrae are variable in number (6-9)
      6. Teeth
              *Lack incisors and canines
              *Cylindrical, homodont, rootless teeth
      7. Rudimentary tail
      8. Long, coarse hair on which blue-green algae grows
      9. Herbivorous: eat buds, flowers, fruit
      10. Very, very low metabolic rate and poor temperature regulation
    2. Family Bradypodidae (3-toed sloths): 1 genus, 3 species
      skull
    3. Family Megalonychidae (2-toed sloths): 1 genus, 2 species
      skull

    4. General characteristics of Family Myrmecophagidae (anteaters)
      1. Very long, tubular rostrums, very small mouths
      2. Long, sticky tongue that moves rapidly
      3. No teeth
      4. Insectivorous
      5. Crush insects with thickened stomach (pyloric portion)
      6. Have large front claws for opening up termite mounds, tearing up rotting logs, etc.
    5. Family Myrmecophagidae - 3 genera, 4 species
      1. giant anteater
      2. tamandua
      3. silky pygmy anteater