Pseudoglyptodon Engelmann, 1987: 217

McKENNA, MALCOLM C., WYSS, ANDRÉ R. & FLYNN, JOHN J., 2006, Paleogene Pseudoglyptodont Xenarthrans from Central Chile and Argentine Patagonia, American Museum Novitates 3536 (1), pp. 1-20 : 3-4

Pseudoglyptodon Engelmann, 1987: 217

TAXONOMIC NOTE: Confusingly, different taxonomic names are currently used to refer to the same minimally inclusive clade encompassing the xenarthran mammals commonly known as sloths: Tardigrada and Phyllophaga. Here we propose phylogenetic definitions (sensu de Queiroz and Gauthier, 1990) to remedy this ambiguity, tying each name to a different clade. We define Phyllophaga (a name coined by Owen, 1842, but generally disused until resurrected by McKenna and Bell, 1997) as all xenarthrans more closely related to Bradypus or Choloepus than to myrmecophagids or dasypodids. Consistent with familiar, present-day usage, we tie the name Tardigrada to the crown clade. Thus, Tardigrada is defined as the most recent common ancestor of Bradypus and Choloepus plus all of its descendants. The distinction between these names is especially relevant to the current study because—as detailed below—new specimens from Chile argue that Pseudoglyptodon is not a member of Tardigrada (the crown clade), but rather that it represents its nearest known outgroup (and hence is a member of Phyllophaga).

TYPE SPECIES OF PSEUDOGLYPTODON : P. sallaensis Engelmann, 1987: 217 . Holotype of P. sallaensis, PU 20552, collected from Branisa’s locality V-12, lower Salla beds, Salla, Bolivia.

OTHER MATERIAL: Other instances of originally described material or references to the presently described material are listed below.

Glyptatelus tatusinus: Ameghino, 1897: 507 , in part. The osteoderm, not the tooth, described by Ameghino (1897: 507, 1902: 48) from the Deseadan of Argentine Patagonia is selected here as the (lecto)type specimen of G. tatusinus . We do this for the same reason as that given by Simpson (1948: 93) in selecting the lectotype of G. fractus . Association of Ameghino’s two syntypes of G. tatusinus is unproven and unlikely, although possible. The tooth referred to G. tatusinus by Ameghino (1897) is clearly related to Pseudoglyptodon and on present evidence refers to that taxon, whatever the relationships of Pseudoglyptodon to other xenarthrans might be. Glyptatelus was made the type of the Glyptatelinae by Castellanos (1932).

Glyptatelus fractus: Ameghino, 1902: 51 or 49, in part. The osteoderm and tooth described by Ameghino, said to be from the Mustersan (couches à Astraponotus ) of Argentine Patagonia, were discussed by Simpson (1948: 93), who selected the osteoderm as the (lecto) type specimen of G. fractus . As with G. tatusinus , no association of the osteoderm with the tooth is evident. The (lecto) type osteoderm is that of an early glyptodont, but the referred tooth, like that of ‘‘ G. tatusinus ’’, is related to Pseudoglyptodon sallaensis , the type species of Pseudoglyptodon . On present evidence this tooth is distinct from other recognized species of Pseudoglyptodon , but the scant material presently known does not yet warrant recognition of a new species. The most complete specimen of this unnamed species of Pseudoglyptodon (to which Ameghino’s referred specimen of G. fractus pertains as well) is AMNH 29483 (see below).

Undescribed glyptateline from Quebrada Fiera, Mendoza Province, Argentina (Scillato-Yane´, 1988): This Deseadan taxon, represented by MLP 79 -XIII-18-9, is known exclusively from osteoderms .

Pseudoglyptodon sp. : Wyss et al. (1990: fig. 4 ), specimen SGO PV 2995. This specimen is designated as the holotype of Pseudoglyptodon chilensis below.

DIAGNOSIS OF PSEUDOGLYPTODON: Slothlike xenarthran with a total of probably just four teeth in each tooth row; first teeth caniniform and massive, lower one with triangular base, upper one with massive oval base; caniniforms followed by just three openrooted molariform cheek teeth, each trilobed and superficially glyptodontlike but without the central figure of glyptodont cheek teeth; skull short, with fused maxilla and premaxilla and fused nasals although the latter are still separate from the maxillae; lacrimal possibly fused to maxilla; large lacrimal foramen; zygomatic arch apparently deep, with weak anterior attachment to skull; lower jaw massive, ventrally everted, with anterior ‘‘spout’’ and underlying large foramen, fused symphysis, low coronoid process, and mandibular condyle.

Figures

Fig. 4. CT scans of the holotype of Pseudoglyptodon chilensis, SGO PV 2995, revealing aspects of this taxon’s dental morphology (dorsal plane). Upper scan, no. 563.18, showing molariform 2 and molariform 3 near the gumline. Lower scan, no. 563.24, illustrating cross sections of the upper canine roots and the upper postcanine dentition, also above the gumline. ‘‘M’’ and ‘‘m’’ signify upper and lower molariform teeth, respectively, as the true positions of these teeth are unknown.