Glyptodonts: Armored sloths, not giant armadillos.

Today three taxa were added
to the large reptile tree (now 720 taxa, subset Fig. 1):

  1. Bradypus (three-toed sloth)
  2. Dasypus (armadillo)
  3. Glyptotherium (glyptodont)

Wikipedia reports, “Glyptodonts are an extinct subfamily of large, heavily armored armadillos. Unfortunately, Glyptotherium the glyptodont nests with Bradypus, the sloth in the large reptile tree – and, as you’ll see… for good reason.

Figure 1. Mammals with a few edentates added. Here glyptodonts nest with sloths, rather than armadillos, contra traditional studies.

Figure 1. Mammals with a few xenarthans added. Here glyptodonts nest with sloths, rather than armadillos, contra traditional studies.

Bradypus is the long-legged arboreal tree-hanging sloth
with fewer toes. Just imagine where the short-legged ground sloth will nest. This hypothesis of edentate relationships runs counter to tradition, but one look at the skulls (Figs. 1, 2) and you’ll wonder why this hasn’t been noticed before.

Figure 2. Bradypus skull from Digimorph.org, used with permission, colors added to select bones.

Figure 2. Bradypus skull from Digimorph.org, used with permission, colors added to select bones. Compare to the glyptodont skull in figure 3. Darker images bring out lighter details.

Both the sloth and the glyptodont
have deep, narrow, flat-topped skulls with a deep ventral process of the jugal and a very short rostrum. These traits, along with a long list of others, split armadillos + aardvarks from sloths + glyptodonts.

Figure 3. Glyptodon skull with select bones colorized. Compare to the sloth in figure 2 and the armadillo in figure 4.

Figure 3. Glyptodon skull with select bones colorized. Compare to the sloth in figure 2 and the armadillo in figure 4.

Here armadillos nest with
aardvarks, like Orycteropus, a clade that was once accepted under the clade Xenartha. According to Wikipedia, xenarthans have extra vertebral articulations, the lowest metabolic rates among therians, the ischium and sacrum are fused and males have internal testicles. Pangolins were once considered xenarthans, but here nest with basal primates.

Figure 4. Skull of the armadillo Dasypus from Digimorph.org, used with permission. and select bones colorized.

Figure 4. Skull of the armadillo Dasypus from Digimorph.org, used with permission. and select bones colorized.

 

Note the nesting of 
whales (Maiacetus) + tenrecs (Hemicentetes), another clade without external testicles. As a scientist, I’m pleased to discover these interrelationships, but a little surprised that no one has seen this before. If you that has happened already, I will be glad to promote those papers here.

Placental mammals
are showing a basal split between carnivores and other insectivore / herbivore placentals (eutherians).