Herein we describe a new, large-bodied species of Pseudoglyptodon, a close sloth ally, from volcaniclastic deposits of the Abanico ( =  Coya-Machalí) Formation of the central Chilean Andean Main Range. This species, P. chilensis, is a rare element of the Tinguiririca Fauna, on which the recently formalized Tinguirirican South American Land Mammal “Age” is founded, being known from just two specimens. The holotype of P. chilensis, a partial skull and largely complete mandibles (preserving seemingly complete upper and lower dentitions), is by far the best-preserved specimen referable to Pseudoglyptodon known. As such, this material permits a more refined phylogenetic placement of this enigmatic xenarthran than has been possible previously, with Pseudoglyptodon representing the proximal outgroup to the clade including the most recent common ancestor of Choelepus and Bradypus, plus all its descendants (i.e., crown clade sloths).

A fragmentary specimen from Argentina is removed from Glyptatelus and referred to Pseudoglyptodon. Although this specimen is distinct from P. chilensis and other previously recognized species of Pseudoglyptodon, it offers too meager a basis for formally establishing a new name.

Finally, phylogenetic definitions of the names Phyllophaga and Tardigrada are proposed. Historically these terms have been used largely interchangeably, but here we advocate linking the latter to the crown clade.