Peltephilus, the horned armadillo, alas, is not an armadillo

Peltephilus ferox is yet another armadillo-mimic. Close to armadillos… but not one.

Figure 1. Peltephilus skull, manus and pes. Note the lack of a palate exposure of the premaxilla, with the canines moving to an anteromedial position formerly occupied by incisors. Otherwise there are 3 premolars and 3 molars present, the standard pattern for sister taxa. Real armadillos have long, narrow rostra with an elongate premaxilla and 7 cone-shaped identical teeth none of which extend below the orbit.  Two species / specimens are shown here.

Figure 1. Peltephilus skull, manus and pes. Note the lack of a palate exposure of the premaxilla, with the canines moving to an anteromedial position formerly occupied by incisors. Otherwise there are 3 premolars and 3 molars present, the standard pattern for sister taxa. Real armadillos have long, narrow rostra with an elongate premaxilla and 7 cone-shaped identical teeth none of which extend below the orbit.  Two species / specimens are shown here. Line art is from Vizcaino and Farina 1997,

In the LRT
Peltephilus (Fig. 1) nests between Glyptotherium (not an armadillo) and Bradypus (a sloth) – but that’s not even the big story (see below) with this highly derived, armored herbivore.

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

Figure 2. Skull of the armadillo Dasypus from Digimorph.org, used with permission. and select bones colorized. Real armadillos have long, narrow rostra with an elongate premaxilla and 7 cone-shaped identical teeth none of which extend below the orbit.

According to
Wkiipedia, “Peltephilus ferox (Ameghino 1887‭; 1.5 m long) the horned armadillo, is an extinct species of dog-sized, armadillo xenarthran mammal which first inhabited Argentina during the Oligocene epoch, and became extinct in the Miocene epoch. Notably, the scutes on its head were so developed that they formed horns protecting its eyes. Aside from the horned gophers of North America, it is the only known fossorial horned mammal. Although it had traditionally been perceived as a carnivore because of its large, triangular-shaped teeth, Vizcaino and Farina argued in 1997 that Peltephilus was a herbivore.”

Figure 3. Subset of the large reptile tree showing the nesting of Barylambda with Orycteropus and Xenarthra.

Figure 3. Subset of the large reptile tree showing the nesting of Peltephilus between Glyptotherium and Bradypus.

Postcranially
Peltephilus had transverse bands of ossified armor along the back. It had short legs and large claws, ideal for digging or ripping open ant colonies.

The teeth are the story here
The seven teeth (x4) of Peltephilus formed a complete arcade. They were all similar in shape. Apparently (based on the above data), like the similarly short-faced Bradypus, the reduced premaxilla did not extend to the palate. No edentates have premaxillary teeth. In Bradypus the lost premaxilla leaves a space between the anterior maxillae. By contrast, in Peltephilus the maxillae join in medial contact. With that medial migration the canine teeth also migrate medially, taking the place of the absent incisors. The remaining 3 premolars and 3 molars comprise the remainder of the arcade with the molars remaining ventral to the laterally expanded jugals, as in sister taxa.

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

Figure 42. Bradypus skull from Digimorph.org, used with permission, colors added to select bones.

Phylogenetic bracketing
confirms the hypothesis of Vizcaino and Farina 1997 that Peltephilus was also an herbivore, not a vicious carnivore as Ameghino 1894 envisioned. Vizcaino and Farina list the following differences with Dasypodidae (Dasypus). Note how many traits here are shared with Bradypus and Glyptotherium [marked with a green dot ]

  1. Short and broad rostrum
  2. Wide nasal (narial) openings 
  3. Short jaw 
  4. Completely fused and expanded mandibular symphysis  
  5. Low condyle  
  6. Teeth with chisel-like occlusal surfaces  
  7. U-shaped tooth row  
  8. Horn-bearing cephalic (head) shield

References
Ameghino F 1894. Enumeration Synoptique des especes de mammiferes fossiles des formations Eocenes de Patagonie. Boletin de la Academia Nacional de Ciencias en Cordoba (Republica Argentina) 13:259-452
Ameghino F 1897. Mamiferos Cretaceos de la Argentina. Segunda contribucion al conocimiento de la fauna mastologica de las capas con restos de Pyrotherium. – Boletin Instituto Geografico Argentino 18:406-521.
Vizcaino SF and  Farina RA 1997. Diet and locomotion of the armadillo Peltephilus: a new view. Lethaia, 30, 79-86.

wiki/Peltephilus

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