PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3536, 18 pp., 4 figures October 19, 2006

Paleogene Pseudoglyptodont Xenarthrans from Central Chile and Argentine Patagonia

1 2 3 MALCOLM C. MCKENNA, ANDRE´ R. WYSS, AND JOHN J. FLYNN

ABSTRACT Herein we describe a new, large-bodied species of Pseudoglyptodon, a close sloth ally, from volcaniclastic deposits of the Abanico (5 Coya-Machalı´) 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.

1 Division of Paleontology, American Museum of Natural History ([email protected]). 2 Corresponding Author, Department of Earth Science, University of California, Santa Barbara, CA 93106 ([email protected]). 3 Division of Paleontology, American Museum of Natural History ([email protected]).

Copyright E American Museum of Natural History 2006 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3536

INTRODUCTION topic dates to roughly 31.5 Ma (Wyss et al., 1993; Flynn et al., 2003)—early Oligocene South America continues to yield enlight- following the time scale of Swisher and ening paleontological surprises. Here we Prothero (1990). The skull preserves much of describe the first-known associated skull and the lower jaws and snout, but rearward from mandibles of Pseudoglyptodon Engelmann, the orbit the specimen is heavily damaged. 1987, from Eocene–Oligocene volcaniclastic Nonetheless, both petrosal bones are in sediments of the Abanico (5 Coya Machalı´) position (although ‘‘floating’’ in the hard Formation, Termas del Flaco, valley of the matrix), as are parts of the right zygomatic Tinguiririca River, central Chile. This is arch and mandibular condyle. All of the the first xenarthran from the Tinguiririca comparatively few teeth of the animal are Fauna (Wyss et al., 1994) to be described present, but the mandibles are clenched in detail. The two Chilean specimens are tightly to the skull. Separation of the mand- referred to a new, large-bodied species of ibles from the skull has not been attempted; Pseudoglyptodon, an aberrant early sloth instead, much of the dental pattern has relative, the type species of which, P. sallaen- been elucidated through computed tomo- sis, is based on a lower jaw from Branisa graphic (CT) scanning. The depositional Locality V-12, lower part of the Salla mechanism(s) accounting for the newly recog- Beds, Deseadan South American Land nized prevalence of mammal remains in Mammal ‘‘Age’’ (SALMA) of Salla, Bolivia post-Neocomian volcaniclastic strata of the (MacFadden et al., 1985). The name ‘‘Pseu- Andean Main Range remain(s) uncertain. doglyptodon’’ is intended to reflect the mor- Specimens described here may have been phology of the cheek teeth of these edentates, superficially resembling the cheek teeth of engulfed in a lahar or volcanic debris flow glyptodontids in their trilobate external and literally cooked to death, with the form, but lacking the central figure (an thinner parts of the skull and jaws reduced axial crest of osteodentine) typical of glypto- to cinders and only the more massive parts dontids. We also refer several teeth from remaining, more or less in their natural the Mustersan and Deseadan of Argentine positions. Postcranial elements were not re- Patagonia—previously interpreted as glyptate- covered, nor were any traces of osteoderms line glyptodontids—to Pseudoglyptodon. The that might have accompanied the skull. new Chilean species, P. chilensis, is similar Moreover, no obvious glyptodontid osteo- to P. sallaensis in many features but is derms are known from any of the localities about twice the size of the latter. A second in the Abanico Formation at Termas del specimen probably referable to P. chilensis Flaco, even though such durable elements is known from Termas del Flaco, but it would be expected to have withstood de- yields limited useful information. A third position. Well-preserved dasypodid osteo- specimen, referable on present evidence to derms occur in moderate abundance in P. chilensis, was described by Florentino strata near Termas del Flaco, but these Ameghino (1897) from the couches a` are unlikely to pertain to Pseudoglyptodon. Pyrotherium (Deseadan in current terminolo- This absence of glyptodontid osteoderms gy) of Patagonia, being placed in the poorly might be argued to reflect the general known early glyptodont species Glyptatelus scarcity of this taxon in these deposits (with tatusinus. only two specimens recovered) rather than The Chilean specimens described here are the taxon’s actual lack of osteoderms. We derived from concretionary nodules harvested would point out, however, that dasypodids, in place from volcaniclastic sediments of the which are known from equally few Abanico (5 Coya Machalı´) Formation of the dental remains in these strata, are nonetheless central Andean Main Range. The Tinguiririca fairly abundantly represented by osteo- Fauna forms the basis of the recently formal- derms—sometimes as large, articulated por- ized Tinguirirican SALMA (Flynn et al., tions of the carapace. In short, if P. chilensis 2003); the age of the fossiliferous strata in possessed obviously glyptodontid dermal ar- this area is constrained by 40Ar/39Ar radioiso- mor, it seems highly unlikely that these would 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 3 have gone undetected, given the extensive SYSTEMATICS collecting efforts undertaken in the area to date. XENARTHRA The dental pattern exhibited by PHYLLOPHAGA OWEN, 1842, Pseudoglyptodon chilensis sheds light on a va- AS MODIFIED BELOW riety of issues concerning xenarthran fossils and phylogeny. It is at once apparent that Pseudoglyptodon Engelmann, 1987: 217 the new Chilean animal is closely similar in most respects but size to Engelmann’s TAXONOMIC NOTE: Confusingly, different Pseudoglyptodon sallaensis from the De- taxonomic names are currently used to refer to seadan assemblage of Salla, Bolivia, and the same minimally inclusive clade encom- passing the xenarthran mammals com- to teeth once referred to two species of monly known as sloths: Tardigrada and the early glyptodont Glyptatelus Ameghino, Phyllophaga. Here we propose phylogenetic 1897, from the Mustersan and Deseadan of definitions (sensu de Queiroz and Gauthier, Argentina. Various features of the skull 1990) to remedy this ambiguity, tying each and mandible of Pseudoglyptodon are name to a different clade. We define Phyl- clearly slothlike, however, as Engelmann lophaga (a name coined by Owen, 1842, but (1987) first appreciated. The newly revealed generally disused until resurrected by occlusion of the caniniform teeth, wherein McKenna and Bell, 1997) as all xenarthrans the lower caniniform tooth occludes almost more closely related to Bradypus or Choloepus directly opposite the upper caniniform tooth, than to myrmecophagids or dasypodids. presages the ‘‘reversed occlusion’’ seen in Consistent with familiar, present-day usage, numerous sloths including Choloepus,and we tie the name Tardigrada to the crown the small number of cheek teeth recalls sloths clade. Thus, Tardigrada is defined as the most as well. recent common ancestor of Bradypus and The new material from Chile clarifies Choloepus plus all of its descendants. The somewhat the problem of glyptateline rela- distinction between these names is especially tionships by reinforcing the disassociation relevant to the current study because—as of the type osteoderms from the teeth dubi- detailed below—new specimens from Chile ously referred to this group by Ameghino argue that Pseudoglyptodon is not a member and accepted by various later commentators of Tardigrada (the crown clade), but (e.g., Hoffstetter, 1958: 573; Scillato-Yane´, rather that it represents its nearest known 1977: 250). We believe that the teeth described outgroup (and hence is a member of by Ameghino as pertaining to two species Phyllophaga). of Glyptatelus instead should be referred to TYPE SPECIES OF PSEUDOGLYPTODON: P. sal- Pseudoglyptodon, an aberrant animal with laensis Engelmann, 1987: 217. Holotype of P. tardigrade affinities now known from more sallaensis, PU 20552, collected from Branisa’s informative material than was available to locality V-12, lower Salla beds, Salla, Bolivia. Engelmann in 1987. Pseudoglyptodon may OTHER MATERIAL: Other instances of orig- have possessed osteoderms, of course, as inally described material or references to did many other xenarthrans (including oro- the presently described material are listed phodonts and mylodonts among sloths), below. but none is known as yet. The new cranial and dental material emphasizes the morpho- Glyptatelus tatusinus: Ameghino, 1897: 507, in logical diversity exhibited by sloths and part. The osteoderm, not the tooth, de- their closest allies as early as the Eocene/ scribed by Ameghino (1897: 507, 1902: 48) Oligocene transition. Although the relation- from the Deseadan of Argentine Patagonia ships of Pseudoglyptodon to sloths or other is selected here as the (lecto)type specimen xenarthrans remain less than ‘‘ironclad,’’ of G. tatusinus. We do this for the same the new information presented here adds reason as that given by Simpson (1948: 93) materially to the potential solution of this in selecting the lectotype of G. fractus. question. Association of Ameghino’s two syntypes 4 AMERICAN MUSEUM NOVITATES NO. 3536

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 Fig. 1. AMNH 29483, mandibular fragment Mustersan (couches a` Astraponotus)of bearing one complete cheek tooth and part of Argentine Patagonia, were discussed by a second, collected by G.G. Simpson from Cerro Blanco, Chubut Province, Argentina. Identified by Simpson (1948: 93), who selected the Simpson (1948: 93) as ‘‘Glyptodont, incertae sedis, osteoderm as the (lecto)type specimen of perhaps Glyptatelus’’, this specimen is here trans- G. fractus. As with G. tatusinus, no associ- ferred to a new, but unnamed, species of ation of the osteoderm with the tooth is Pseudoglyptodon. Reproduced from Simpson evident. The (lecto)type osteoderm is that of (1948: 93, fig. 23). Scale, 23. an early glyptodont, but the referred tooth, like that of ‘‘G. tatusinus’’, is related to separate from the maxillae; lacrimal possibly Pseudoglyptodon sallaensis, the type species fused to maxilla; large lacrimal foramen; of Pseudoglyptodon. On present evidence zygomatic arch apparently deep, with weak this tooth is distinct from other recognized anterior attachment to skull; lower jaw mas- species of Pseudoglyptodon, but the scant sive, ventrally everted, with anterior ‘‘spout’’ material presently known does not yet and underlying large foramen, fused symphy- warrant recognition of a new species. The sis, low coronoid process, and mandibular most complete specimen of this unnamed condyle. species of Pseudoglyptodon (to which Ameghino’s referred specimen of G. fractus Pseudoglyptodon, unnamed species pertains as well) is AMNH 29483 (see below). REFERRED SPECIMENS: AMNH 29483 Undescribed glyptateline from Quebrada (fig. 1), a mandibular fragment bearing one Fiera, Mendoza Province, Argentina complete cheek tooth and part of a second, (Scillato-Yane´, 1988): This Deseadan taxon, discussed and figured by Simpson (1948: 93, represented by MLP 79-XIII-18-9, is known fig. 23) as ‘‘Glyptodont, incertae sedis, perhaps exclusively from osteoderms. Glyptatelus’’, and also in more general terms Pseudoglyptodon sp.: Wyss et al. (1990: fig. 4), by Hoffstetter (1958: 573, fig. 25). A cheek specimen SGO PV 2995. This specimen is tooth from the Mustersan (or later; see below) designated as the holotype of Pseudoglypto- of Patagonia referred by Ameghino (1902) don chilensis below. to Glyptatelus fractus is here referred to Pseudoglyptodon, pertaining to the same un- DIAGNOSIS OF PSEUDOGLYPTODON: Slothlike named species as AMNH 29483. xenarthran with a total of probably just LOCALITY INFORMATION: Cerro Blanco, four teeth in each tooth row; first teeth Chubut Province, Argentine Patagonia. caniniform and massive, lower one with Simpson (1948) provided no precise informa- triangular base, upper one with massive oval tion about the provenance of AMNH 29483, base; caniniforms followed by just three open- nor is the specimen mentioned in his un- rooted molariform cheek teeth, each trilobed published field notes. Nevertheless, the speci- and superficially glyptodontlike but without men’s label reads, ‘‘Musters Formation, F5 the central figure of glyptodont cheek teeth; beds, Cerro Blanco, Expedition ’30.’’ The skull short, with fused maxilla and premaxilla provenance of Ameghino’s specimen is un- and fused nasals although the latter are still certain. 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 5

AGE: Mustersan, according to Simpson a massive, purplish brown, volcano-sedimen- (1948). The Mustersan, traditionally consid- tary horizon, near the apparent local base of ered medial Eocene in age, has recently been the formation. Owing to structural complex- suggested to be substantially younger, i.e., to ity, it has not been possible to establish the postdate 35–36 Ma (Kay et al., 1999). relative stratigraphic position of the fossilifer- DIAGNOSIS: Cheek-tooth wall of hard den- ous horizon within the approximately 2-km- tine thicker than in P. sallaensis and lobes less thick Abanico Formation. A second, sub- angular. Differs from P. chilensis in smaller stantially older fauna has been recovered from size (the lower tooth row being ,30% shorter volcaniclastic sediments of the Tinguiririca anteroposteriorly). Valley some 15 km west of those hosting COMMENT: These small Pseudoglyptodon P. chilensis (Flynn et al., 1991; Wyss et al., cheek teeth are evidence of little but the 1996), indicating that the Pseudoglytodon- presence of the taxon in Mustersan deposits, producing beds do not correspond to anything but this at least confirms other pre-Deseadan approaching the lowest stratigraphic levels records for early phyllophagans in South in the formation. Still further to the west America (Hoffstetter, 1958: 573). (,20 km), but still at the same latitude (35uS), thick exposures of the Abanico Formation Pseudoglyptodon chilensis, new species have yielded three stratigraphically super- posed fossil mammal faunas, the lowest of which also clearly predates the Tinguirirican Pseudoglyptodon sp.: Wyss et al. (1990: fig. 4). SALMA (Wyss et al., 2004). TYPE SPECIMEN: SGO PV 2995, damaged AGE: Tinguirirican SALMA. The diverse skull and mandibles with seemingly complete fauna co-occurring with Pseudoglyptodon at dentition. Termas del Flaco allows unambiguous corre- TYPE LOCALITY: The type and referred lation with the SALMA sequence. The ab- Chilean specimens are from the Tinguiririca sence of such diagnostic taxa as Pyrotherium, River valley (,35uS) in the Cordillera primates, mesotheres (which is problematic, Principal of the Central Andes, approximately because this group occurs in the Divisaderan), 7 km west of the Argentine border. They are Archaeohyrax, Plagiarthrus, hegetotheres, and derived from a steep set of exposures north of Morphippus (Marshall et al., 1983) indicates an unnamed pass (the latter of which is a pre-Deseadan age for this Chilean fauna. identified by its 2738 m elevation on the Co-occurrence of taxa known elsewhere only topographic sheet [Anonymous, 1985]), ap- from Mustersan and older deposits (notosty- proximately 3 km south of the summer resort lopids, notopithecines, and polydolopids) with town of Termas del Flaco. Pseudoglyptodon taxa previously known only from younger chilensis and its associated fauna occur in beds (a clade of notohippids diagnosed by 35–50u westward-dipping volcaniclastic depos- hypsodont incisors, interatheriine interatheres, its of various colors, dominantly brownish and rodents) identifies the fauna as represent- red, interbedded with volcanic flows and ing a biochronologic interval interposed be- tuffs (fig. 2). Prior to discovery of fossil tween the Deseadan and Mustersan SALMAs, mammals in the region (Novacek et al., the Tinguirirican (Flynn et al., 2003). In this 1989) these deposits were mapped as pertain- connection, the Pseudoglyptodon-containing ing to the Colimapu Formation of poorly fauna from Chile bears little resemblance constrained Aptian–Albian age (e.g., Klohn, to the problematic Divisaderan assemblage 1960). More recent detailed mapping and (known from a single locality some 250 km associated geochronologic studies (Wyss to the northeast, in western Argentina). et al., 1993; Charrier et al., 1996) indicate Whatever the still uncertain relative temporal that the mammal-producing unit pertains relationship of the faunas from Termas del to the Abanico Formation (5 Coya-Machalı´ Flaco and Divisadero Largo may be, the two Formation), a widespread and stratigraphi- are undoubtedly distinct. cally important unit in this region of the That the Tinguririca Fauna derives from Andes. Fossils occur most abundantly in a thick volcanic and volcaniclastic sequence is 6 AMERICAN MUSEUM NOVITATES NO. 3536

Fig. 2. View east of the fossiliferous outcrop (2–3 km south of Termas del Flaco, Chile, and immediately northwest of an unnamed pass of 2738 m elevation [Anonymous, 1985]) from which the two known specimens of Pseudoglyptodon chilensis were recovered. The view is roughly perpendicular to the strike of the 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 7

fortuitous from the standpoint of radioisoto- DESCRIPTION: Skull: The skull of pic dating. Multiple single-crystal laser fusion Pseudoglyptodon chilensis (fig. 3) is evidently 40Ar/39Ar dates (Wyss et al., 1993) and fewer short, as suggested by the small number of conventional 40K/40Ar analyses (Wyss et al., teeth, the position of the jaw articulation, and 1990) constrain the absolute age of the position in the matrix of the two petrosal Pseudoglyptodon chilensis. Dates from imme- bones. The distance between the front of the diately above the fossiliferous horizon indicate skull and the anterior edge of the orbit (as P. chilensis to be minimally ,31.5 Ma (early judged by the position of the lacrimal fora- Oligocene) in age (Flynn et al., 2003). Levels men) is truncated, a condition generally seen immediately below the fossiliferous horizon in sloths but even more marked in glypto- (but within the same stratigraphic unit) have donts. The little of the orbit that may be been dated (Flynn et al., 2003) at a locality discerned occurs not far above the roots of the producing a fauna indistinguishable from the upper cheek teeth, which, although almost one associated with P. chilensis, but this certainly hypselodont (no evidence of closed second locality has not yet produced P. roots is seen on the CT scans—which are chilensis itself. Present evidence suggests, frontal sections), are not highly elongate albeit indirectly, that the Tinguirirican prisms requiring a deep maxilla. Because all SALMA likely extends no further back in upper teeth appear to originate in the maxilla time than an additional 1–2 Ma (Flynn et al., and no suture is evident at the anterior end 2003), i.e., very near the Eo-Oligocene transi- of the maxillary wall of the rostrum, the tion. premaxilla was either lost postmortem or is REFERRED SPECIMENS: A second specimen completely fused to the maxilla in the speci- from Termas del Flaco, SGO PV 2999, men at hand. The two nasal bones are fused to consists of a badly damaged anterior end of each other but not to the maxilla. They extend a right mandibular ramus and part of the posteriorly to at least a position over the fused symphysis. Only alveoli and fragmen- posterior end of the first molariform upper tary tooth bases remain. One alveolus suggests cheek tooth, but damage obscures their full a trilobed cheek tooth like that of the type posterior extent and whether they widened in specimen of P. chilensis. Unfortunately, the the rear. The nasals are thus quite long and referred specimen from Termas del Flaco thin, contrasting with the short wide nasal provides little useful information. A judged to be typical—and ambiguously syna- Deseadan cheek tooth from Patagonia re- pomorphic—of tardigrades (Gaudin, 2004— ferred by Florentino Ameghino (1897: 507) to his character 100); foreshortened nasals are Glyptatelus tatusinus, not demonstrably asso- also typical of glyptodonts. In SGO PV 2995 ciated with the (lecto)type specimen and not the right nasal is ,5 mm wide at the midpoint a glyptodont in any case, may belong here of its preserved portion, while the element was as well. It provides limited information but is at least 30 mm long and quite likely reached less certainly conspecific with P. chilensis than twice that length originally. Striking features is SGO PV 2999. of the otherwise already bizarre dentition of DIAGNOSIS: Pseudoglyptodon chilensis dif- P. chilensis are the massive upper and lower fers from P. sallaensis and the unnamed ‘‘canines.’’ The oval, upper caniniform tooth species discussed above in the former’s much base is housed in a prominent bulge in the larger size, thinner cheek-tooth wall of hard maxillary bone on the side of the snout. The dentine, and more sharply angular cheek- snout is too damaged to provide information tooth lobes. about the anterior end of the palate, housing r west-dipping strata. Fossil mammal localities occur in the dark band of volcaniclastic sediments of the Abanico (5 Coya Machalı´) Formation in the mid-foreground (straddled by the top half of the circle). A cluster of tents in the circle gives a sense of scale. The light-colored strata in the middle distance are of the Ban˜os del Flaco Formation (Neocomian), with the snow-covered rocks in the distance belonging to the Rı´o Damas Formation (Kimmeridgian). The horizon approximates the border with Argentina. 8 AMERICAN MUSEUM NOVITATES NO. 3536

Fig. 3. Lateral view of the holotype of Pseudoglyptodon chilensis, SGO PV 2995. Visible near the base the coronoid process, appressed against the ventrolateral margin the mandibular ramus, is a thin fragment of bone interpreted as a remnant the descending process of the jugal. Wedges of the anterior and posterior parts of the base of the lower caniniform are visible immediately linguad of the upper caniniform, reflecting the unusual side-to-side occlusion of these enlarged anterior teeth. for the organ of Jacobson, septomaxillary the coronoid process, and outboard of the last bone if any, or other anterior structures. The upper and lower cheek teeth. This element narial opening was large, but apparently little (obviously not part of the mandible) sits at flared. Details of the orbit are lacking due to a considerable distance from broken base of damage, but the orbit was probably not large. the anterior root of the zyomatic arch. An apparent lacrimal bone occurs on the right Nevertheless, if this element is in anything side, where it appears to be fused to the close to its life position, it can only represent maxilla. Its large lacrimal foramen lies anteri- a distal portion of an elongated ventral or to the orbital rim. The anterior end of process of the jugal. The leading edge of a possibly deep, posteroventrally descending this element is seemingly smooth and un- wing of the anterior part of the zygomatic arch broken, its orientation consistent with that arises between the lacrimal foramen and the expected for a descending process of the jugal, anterior end of the second of the three as seen in many sloths. The possibility that molariform upper cheek teeth. Although the this element represents a displaced element maxillary part of the arch does not appear to from the skull roof or orbit cannot be have been especially strong (judged from its completely excluded, however. If this element broken cross section), there is circumstantial is indeed a portion of the zygomatic arch, it evidence of a strong descending process of the resembles much more the condition seen in jugal. A thin, triangular fragment of bone is tardigrades than in glyptodontids (wherein the appressed against the dorsoexterior border of descending process is much more anteriorly the right mandibular ramus near the base of situated). 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 9

The zygomatic arch was probably not occurs near the midpoint of the third lower continuous with the squamosal, but evidence molariform tooth; this, coupled with the slow is weak. We have not seen the infraorbital rate of climb of the ascending process, results foramen, but it may be obscured by breakage in the cheek teeth being exposed in lateral view and unremoved matrix. No traces of the (i.e., not covered by the ascending process), frontals remain, unless one of several frag- save for the posterior third of the last lower ments of bone above the right lacrimal teeth and the posteroventral corner of last foramen represents the anterolateral corner upper teeth. Importantly, there is no evidence of the right frontal. The parietals, squamosals, of an external opening of the posterior occipitals, alisphenoids, basisphenoid, basioc- mandibular canal near the horizontal–ascend- cipital, vomer, pterygoids, and certainly any ing ramus junction. Although the inferior possible mesethmoid are all now absent, but portion of the horizontal ramus is broken on the rear of the palate, presumably involving the right side of SGO PV 2995, enough is the palatine bones, extends to the rear past preserved to demonstrate that no such fora- and around the posterior lobe of the last upper men was present. The occurrence of a foramen molariform cheek tooth, forming an indented in this region uniquely characterizes tardi- torus of sorts that may incorporate a part of grades among xenarthrans (Gaudin, 2004). the palatine as well as the maxilla. The palate Owing to the shelf of bone lateral to the is unusually narrow between the cheek-tooth third lower molariform mentioned previously, rows (best seen on CT scan images). At the the ascending process occupies a plane sub- gumline the two upper tooth rows are nearly stantially lateral to the cheek-tooth row. The parallel centrally but diverge slightly anterior- ascending process appears to be small, un- ly (particularly from the first molariform excavated either laterally or medially, evident- tooth forward) as well as posteriorly (partic- ly not projecting upward or rearward very far. ularly m3). Breakage of the dorsal, posterior, and ventral The lower jaw is massive, especially in the borders of the process, however, obscures its symphyseal area, which is fused but shows original size and shape. A small, detached traces of the suture on SGO PV 2995 but not knob of bone floating in the matrix near the on SGO PV 2999. The horizontal rami bulge posteroventral corner of the preserved part of laterally beginning below the second molari- the ascending ramus may be a remnant of the form tooth, extending and becoming more right mandibular condyle. If so, the condyle is pronounced posteriorly. This results in a ,5- positioned low, near the plane of occlusion, mm-wide shelflike area lateral to the third just in front of and lateral to the right petrosal. molariform tooth. The anterior end of the jaw This contrasts with the primitive condition supports a short upturned ‘‘spout,’’ below seen in most sloths (except mylodontids and which lie one large and several smaller mental Choloepus) and dasypodids (glyptodontids foramina on each ramus. Immediately behind included), wherein the condyle is positioned the ‘‘spout’’ is the massive base of the lower well dorsal to the tooth row (Gaudin, 2004). caniniform tooth, which is followed by the Nothing can be said of the posteroventral three molariform lower cheek teeth (which are parts of the mandible. A trace of a robust set off from each other by short diastemata). hyoid bone may possibly be represented by The lower cheek-tooth rows diverge poste- a bone fragment in the matrix at the appro- riorly, especially deep within the alveoli. priate position anterior to the right petrosal However, their occlusal surfaces meet those and medial to the presumptive mandibular of the upper cheek-tooth row with less condyle. posterior divergence. Dentition: The significance of SGO PV 2995 The ascending process of the mandible was revealed on the outcrop when its melon- arises from the side of the horizontal ramus sized encasing nodule was delicately cleaved lateral to the last lower molariform cheek with a sledge hammer; just the surface of the tooth, slanting up at an angle of about 135u to anterior end of the left mandible was visible the plane of occlusion. The junction of the initially. Mechanical preparation revealed the ascending and horizontal rami of the mandible labial faces of the teeth. Because the mandibles 10 AMERICAN MUSEUM NOVITATES NO. 3536 are tightly clenched, however, it has not been Nevertheless, as with other xenarthrans, until possible to disengage the upper and lower detailed embryological work is carried out, the dentitions. Computerized tomography was homology of these teeth remains uncertain. used to more fully elucidate the dental It seems plausible, however, that either the morphology of SGO PV 2995. Twenty CT upper or the lower caniniform tooth in cross sections, taken as parallel to the occlusal Pseudoglyptodon is not a true canine, because plane as possible (CT scan nos. 563-11 the occlusion of these teeth, as in sloths, differs through 563-30) were generated by Scientific from that seen in other mammals. This Measurement Systems, Inc., (Austin, Texas) conclusion assumes that an anterior premolar using a 420-kV 3-mA X-ray source. This stack can be more readily transformed into a canine of slices ranges from the bases of the lower imposter, than the position of true canines can cheek teeth to above the roots of the upper be shifted anteriorly or posteriorly relative to molariform cheek teeth. Distance in the x the opposing tooth. Regardless of whether direction is 128.8 mm (i.e., preserved skull phyllophagan ‘‘canines’’ are C1/p1, C1/c1, or length), and distance in the y direction is some other permutation, tardigrades are 61.8 mm (i.e., preserved skull width). Each unique among xenarthrans in having upper slice is 0.25 mm thick. Separation of the slices tooth rows extend anterior to the lower tooth is 2.5 mm. The following description is based rows. On the damaged left side of SGO PV largely on this CT imagery. It must be 2995 the lower caniniform appears to occlude cautioned that although the CT scans roughly behind the upper, but on the better preserved parallel the occlusal plane, because the vertical right side the upper and lower caniniforms sit axes of the high-crowned teeth are not side by side. Thus, the upper and lower tooth consistently normal to this plane, the tooth rows of Pseudoglyptodon terminate at nearly outlines seen on the scans are distorted by the the same level anteriorly. Pseudoglyptodon is progressively more oblique angle at which therefore alone among xenarthrans in this they were sectioned (fig. 4). This is particular- regard, bearing an apomorphic resemblance to ly true for sections taken the greatest distance the condition seen in tardigrades (where the from the occlusal plane, especially for the upper tooth row extends anterior to the posterior postcanines, whose apparent bucco- lower). Some artiodactyls convert an anterior lingual dimensions are exaggerated near the lower premolar into a caniniform tooth that tooth bases owing to canted and slightly occludes behind the upper canine, but the bowed vertical axes of these teeth. resemblance to sloths is not as close as that The number of teeth in Pseudoglyptodon is seen in Pseudoglyptodon. unusual, probably just four above and four The lower caniniform tooth of Pseudo- below on each side, all fairly closely spaced glyptodon occludes with the sloping postero- with only short gaps between them. A more medial wear facet of the upper caniniform substantial gap behind the upper caniniform tooth, much as in Choloepus except that, in tooth on the specimen’s left side is likely Pseudoglyptodon, the lower tooth is more artifactual, as a large crack disrupts the medially placed relative to the upper. The specimen in this region. Additionally, the occlusal relationship of these teeth is best degree to which the upper and lower left exhibited on the right side of SGO PV 2995 caniniforms are compressed into each other (fig. 3), because postmortem deformation has anteroposteriorly suggests a small degree of damaged the left pair of caniniforms. On the postmortem distortion in this region of the right side, the upper and lower caniniforms specimen. It is uncertain whether teeth oc- sit in a more normal orientation, directly side curred anterior of the upper caniniforms, by side, the medial surface of the upper tooth because that region of the rostrum is missing. occluding against the lateral side of the lower. The caniniform teeth of Pseudoglyptodon Judged from the CT scans, the tip of the may or may not be true canines. Grasse´ (1955) lower caniniform tooth was not accommodat- regarded the anterior teeth in sloths to ed by an excavation in the palate. The three represent the true canine of the upper tooth molariform cheek teeth following the canini- row and the first premolar of the lower. form tooth on both the upper and lower tooth 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 11

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. rows are anteroposteriorly elongate and tri- really a root in the usual sense) that extends lobed, being about as high as they are long. It high into the maxilla. At its dorsal extremity cannot be established whether any of the teeth the base of the upper caniniform tooth opens is deciduous, or had replaced a precursor. widely rather than closing to a blunt tip. CT The upper caniniform tooth is enormous sections of the unworn parts of the tooth are and is supported by a large oval base (not narrower at the front than the rear, and the 12 AMERICAN MUSEUM NOVITATES NO. 3536 labial wall of the tooth is relatively convex, The first of the three upper molariform whereas the lingual wall is flatter. A rather flat cheek teeth is the smallest of the upper transverse wear facet has been created by postcaniniform series and is the narrowest action with the lower caniniform tooth, from transversely. Its anterior lobe is flattened and the recurved anterior tip of the upper canini- oriented normal to the tooth’s anteroposterior form tooth diagonally upward until the facet axis deep within the alveolus. Near the occlusal reaches the broad rear of the tooth’s base at surface the flat anterior surface faces more the gum line. linguad. The isthmus between the anterior and The lower caniniform tooth differs in shape medial lobes is narrower than in the two more from its upper counterpart. CT scans show that posterior upper cheek teeth. The medial lobe is its massive open base is wide in front and nearly blunter and projects less than those of the flat on the anterior face within the alveolus. It succeeding teeth, and the posterior wall of the then narrows, followed by a narrower rear- posterior lobe is more flattened. The indenta- projecting lobe. The cross sections within the tions demarcating the lobes of the molariform alveolus thus have a ‘‘pinched,’’ triangular teeth are less pronounced on the lingual walls of shape. Near the gum line, the broad anterior the teeth than they are labially. Both the face of the lower caniniform tooth becomes anterior and posterior labial lobes diverge from more rounded, and the posterior lobe becomes one another strongly, in contrast to those of the even narrower. Above the gum line, the anterior succeeding teeth. face is transversely worn by the action of the The second of the molariform upper cheek upper caniniform tooth. The diagonal (antero- teeth is more symmetric about its medial lobes ventral–posterodorsal) slope of the transverse than the first, although the labial reentrant wear facet is guaranteed by the initial wear that between the anterior and medial lobes seems would have occurred when these curiously to have a small secondary fold high above the shaped teeth first made contact. present occlusal surface (at least on the As with the caniniforms, the homologies of specimen’s right side). The anterior wall of the molariform teeth in Pseudoglyptodon are the anterior lobe and the posterior wall of the uncertain. All three molariform cheek teeth in posterior lobe are gently convex. The medial both the upper and lower dentition have lobe is smaller and less acute than that of essentially the same trilobed external shape the third molariform tooth. As on the first of glyptodont teeth, in outline reminiscent of molariform tooth, the anterior and posterior a bat in flight seen from directly below. The lobes of the second diverge labially more than long axes of these teeth parallel the long axis lingually, contrasting with the orientation of of the tooth row. As in glyptodontids, the the lobes of the posterior tooth. crowns of these teeth are worn nearly flat The third (and last) upper molariform cheek except for the anterolabial lobe of the right tooth is the largest of the upper series. The third lower molariform cheek tooth, which anterior wall of its anterior lobe is gently projects somewhat between the second and convex and is not subdivided by an anterior third upper molariform cheek teeth labially in indentation, as is its lower counterpart. The a manner reminiscent of the anterior ends of posterior lobe is broad, with a flattened, the crowns of rear lower molariform cheek posterolabially facing wall that is indented teeth of Orophodon and Octodontotherium slightly on the animal’s left tooth but not on (Hoffstetter, 1958: fig. 42). The various the right one. Both the anterior and posterior molariform cheek teeth change slightly in lobes are more acute labially than lingually, shape with wear, as seen in their various cross but the prominent medial lobe is acute both sections, but they do not change significantly lingually and labially, forming the widest part in dimensions throughout the various levels of of the tooth. Breakage of the maxilla posterior each tooth. The base of each molariform to the last left molariform reveals that this cheek tooth is open, as in most tooth-bearing tooth is implanted such that its vertical axis xenarthrans. Unlike glyptodont molariform slopes labially from top to bottom. cheek teeth, there is no central figure in the The symphysis of SGO PV 2995 is well dentine of teeth of Pseudoglyptodon. enough preserved that the presence of any 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 13 lower teeth anterior of the caniniforms seems than labially. The medial lobe is smaller and, unlikely. Confoundingly, SGO PV 2999 ex- like the other lobes, more pronounced lingual- hibits the broken stubs of two small teeth ly than labially. floating in matrix above the symphyseal The third molariform, the largest lower region. Both consist of little more than cheek tooth, is distinguished by a very large broken, ovoid cross sections 2–3 mm in di- and transverse anterior lobe that is markedly ameter. Nevertheless, these tooth remnants indented anteriorly, resulting in a large, are positioned symmetrically (one on either rounded lingual sublobe and a smaller, some- side of the symphysis, and about 1 cm apart what more acute labial one. The medial lobe is from one another), so it must be assumed that also very large, transverse, and acute on both they are preserved in life position. What are sides of the tooth, but it is especially promi- these teeth? Two explanations seem credible. nent lingually. The posterior lobe is somewhat The bone–matrix interface on SGO PV 2999 asymmetrically placed, lying mainly postero- is indistinct anteriorly, making it difficult to labially, somewhat the mirror image of the determine what these teeth were originally anterior lobe of the first molariform tooth. As attached to. Nevertheless, there is a distinct in the other lower molariform cheek teeth, it is rim of bone immediately lateral of the right more acute labially than lingually. Breakage of tooth—this rim is clearly the medial margin of the dentary posterior to molariform 3 on the an alveolous for an enlarged anterior lower left side of SGO PV 2995 shows this tooth to tooth, probably the caniniform. The medial be inclined lingually. It also shows clearly that position of this tooth relative to the mandib- the root of this tooth is quite short compared ular alveolus suggests that both tooth rem- with the second molariform of P. sallensis.In nants are likely the tips of the upper canini- the latter, the second molariform reaches the forms (which were clenched), the remainder of base of the mandible, and the tooth is nearly the upper dentition having been broken away. 3 cm high (i.e., the height is triple the length). Alternatively (but less likely), these tooth In the Chilean form the molariforms are remnants could represent small anterior teeth subequal in height and width. of the lower dentition, elements which simply Petrosals: Although both petrosals are pre- are not preserved in SGO PV 2995. served (indeed, they constitute nearly the The first lower molariform is the smallest entirety of the preserved portion of the skull cheek tooth, and has the narrowest isthmuses posterior to the upper dentition), neither between lobes. The anterior lobe lies mainly reveals much anatomical or phylogenetically anterolabial to its isthmus, with the result that informative data. The left petrosal consists of there is little or no anteroposterior curvature a badly damaged, featureless lump. The right of the lingual wall of the tooth anterior to the petrosal preserves perfectly ordinary-looking medial lobe. The medial lobe projects slightly oval and round windows, and an unremark- labially, but forms a larger and more acute able promontorium. projection on the lingual side, limiting the anterior end of a deep reentrant behind it. The PSEUDOGLYPTODON posterior lobe is more symmetrical than the PHYLOGENETICS offset anterior one, and it is slightly indented at the rear. It is the widest and most massive Is Pseudoglyptodon a sloth? This of course lobe. depends on one’s definition of ‘‘sloth’’. The second lower molariform tooth is larger Pseudoglyptodon clearly falls phylogenetically than the first and bears a large posterola- outside the minimally inclusive clade of which bially–anterolingually oriented anterior lobe, Bradypus and Choloepus are a part, i.e., it is the anterolabial wall of which is nearly flat. the nearest outgroup to what has traditionally The lingual part of the lobe is larger and less been termed sloths. Is it preferable to amend acute than the labial part. The posterior lobe the definition of ‘‘sloth’’ such that it is is even larger than the anterior one but is applicable to Pseudoglyptodon as well, or oriented somewhat posterolingually–anterola- should a different name be defined for the bially. It too is larger and less acute lingually minimally inclusive clade of xenarthrans of 14 AMERICAN MUSEUM NOVITATES NO. 3536 which Pseudoglyptodon is a member? As Pliocene of western Brazil (Santos et al., mentioned earlier, the recognition of two 1993), may hint that this pattern was primitive new species of Pseudoglyptodon herein pre- for sloths. This had been suggested earlier sents an excellent opportunity to rectify a long- by incomplete orophodont dentitions contain- standing nomenclatural problem, the existence ing several sequential bilobed teeth. Thus, of two names (Tardigrada and Phyllophaga) the cheek-tooth outline exhibited by that have been employed nearly interchange- Pseudoglyptodon may represent: (1) a still ably in xenarthran systematics in reference to more primitive condition (wherein sloths the same group. We have opted to attach the may have been characterized ancestrally by former to the crown clade, using the name trilobed cheek teeth behind simpler canini- Phyllophaga to refer to all xenarthrans more forms); (2) an autapomorphic modification to closely related to sloths (Tardigrada) than to three lobes from the bilobed condition seen anteaters or armadillos. Following this usage, in some early, Octodontobradys-like oropho- we are confident that Pseudoglyptodon is donts; or (3) a completely independent deri- a member of the Phyllophaga, but it is almost vation from an unlobed ancestral condition. certainly not a tardigrade. Beyond the unusual outline of the cheek A number of features argue for the out- teeth in Pseudoglyptodon, the departure of this group placement of Pseudoglyptodon relative taxon’s dental formula (4/4) from the pattern to Tardigrada. In common with tardigrades, typical of tardigrades (5/4) should also be Pseudoglyptodon apomorphically possesses emphasized. Pseudoglyptodon retains fully a short, deep skull and robust mandibles. functional caniniforms, meaning that the re- Anteriorly the mandibles of Pseudoglyptodon duction of the upper dental count was likely bear a spoutlike structure and a large foramen achieved through the loss of the first or the like that of tardigrades. There is no posterior last molariform. Thus, it seems inescapable opening of the mandibular canal in that this and potentially other aspects of Pseudoglyptodon’s dental anatomy do not Pseudoglyptodon, contrasting with the condi- typify phyllophagans ancestrally (nor any tion in tardigrades. There are likely only four other group of xenarthrans to which this upper and four lower teeth on each side in taxon is potentially related). Given the Pseudoglyptodon, of which the most anterior early age of Pseudoglyptodon, its high are caniniform. This represents a reduction of degree of aberrant dental specialization is the dental formula from the five upper teeth/ unexpected. four lower teeth considered ancestral for In a superb recent assessment of tardigrade tardigrades (Gaudin, 2004). The enlarged relationships, Gaudin (2004) identified 22 caniniform teeth of Pseudoglyptodon occlude nonauditory cranial features as unambiguous- in a manner approaching the condition seen ly diagnostic of the group. Of these, currently in some tardigrades; in sloths having canini- available specimens of Pseudoglyptodon per- form teeth, the upper one occludes anterior mit scoring of only the following (using to the lower one (the reverse of the situation Gaudin’s character/character state numbering seen in most mammals). By contrast, in scheme). Gaudin’s analysis did not include Pseudoglyptodon the caniniforms occlude glyptodonts, however, so we caution that nearly side by side. The cheek teeth of several of these features are not unique among Pseudoglyptodon are hypselodont and tri- xenarthrans. lobed, reminiscent of glyptodont teeth in these respects, but lacking the central dentine figure 37(3): Depth of mandible .22.5%, #25% of of glyptodontids. In our estimation, the closest approach to the dental pattern of maximum mandibular length. This number Pseudoglyptodon among tardigrades is seen is difficult to estimate in Pseudoglyptodon in various mylodonts, a group generally due to breakage, but the maximum man- recognized as having diverged early in the dibular length is ,10 cm. The mandible history of sloths. Among these, orophodontids of P. chilensis is 2.5 cm deep at a minimum, may be singled out. The bilobed cheek teeth of and probably approached 3 cm in life. Thus, Octodontobradys puruensis from the Mio- mandibular depth in Pseudoglyptodon meets 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 15

or exceeds the primitive sloth condition, Mylodon. Nevertheless, the dental formula potentially matching the most extreme seen in Pseudoglyptodon (4 uppers, 4 lowers) deepening seen among tardigrades, e.g., closely approaches that typical of tardi- Acratocnus, Megatherium, and Octomy- grades ancestrally. lodon (Gaudin, 2004). Glyptodont mand- 7(1): Hypsodont cheek teeth. Pseudoglyptodon ibles are also deep, which is interpreted here is clearly high crowned, and moreover is as homoplasy. hypselodont. P. chilensis shows that early 61(1): Fused mandibular symphysis. Fusion members of Pseudoglyptodon are substan- of the symphysis in Pseudoglyptodon argues tially less hypsodont than the slightly that this feature is diagnostic of Phyllophaga. younger P. sallaensis. Glyptodonts also A fused symphysis occurs also in glypto- have hypso- and hypselodont cheek teeth, donts, presumably homoplastically. presumably independently derived. 74(1): Posterior external opening of mandib- 9(2): Modified orthodentine core of teeth, ular canal. Absent in Pseudoglyptodon. large, typically well vascularized. Although 85(3): Length of snout (preorbital length the degree of vascularization has not measured to tip of nasal) ,25%, $15% of been assessed in Pseudoglyptodon, the basonasal length. In Pseudoglyptodon the teeth are nonetheless quite large for a xenar- basonasal length is ,12 cm. The preorbital thran. length is less securely known given 11(2): Outer layer of cementum forms thick breakage of the anterior rostral region in layer around outside of teeth. There is no SGO PV 2995; we estimate it to be between obvious evidence of cementum on the teeth 3 and 4 cm. Although there is considerable in Pseudoglyptodon. variability in the length of the snout in 18(1): Upper tooth row extends anterior to tardigrades, the condition in Pseudo- lower. This condition is just barely met in glyptodon clearly more closely resembles Pseudoglyptodon, judging from the less the rostral form typically seen in that group distorted right side of SGO PV 2995. than it does the form in cingulates (except 20(1): Wear surface on C1/c1 oblique. glyptodonts) or myrmecophagids. 36(6): Trilobate m3. Among xenarthrans, 142(2): Lacrimal foramen large, diameter Pseudoglyptodon is remotely comparable $2.5%, ,3% of basonasal length (BNL). only to glyptodonts in this respect. The diameter of the lacrimal foramen in 100(0): Length and width of nasals. Pseudoglyptodon is ,3 mm, i.e., roughly Tardigrades are typified (ambiguously) by 2.5% of BNL. short wide nasals, the ratio of maximum 145(2): Jugal with large ascending and des- length to width measured at midpoint ,3. cending processes. Although the ascending In Pseudoglyptodon this ratio is .6, prob- process is not preserved in Pseudoglyptodon, ably approaching 12, being difficult to this taxon appears to have been marked by estimate due to anterior and posterior a strong descending process. damage to the nasals. Slightly less In addition, there are a number of derived elongated nasals (length:width ratio .4) features seen in Pseudoglyptodon that are uniquely (and apomorphically) typifies optimized as ambiguously synapomorphic Scelidotheriinae among tardigrades. Pseu- for Tardigrada by Gaudin (2004, his node 6). doglyptodon is quite unusual in this respect, probably reflecting the condition marking 2(2): Dental formula: 5 upper teeth, 4 lower pilosans primitively. Glyptodonts are also teeth. Pseudoglyptodon should actually be characterized by short wide nasals. scored with Gaudin’s character state 3 (i.e., 153(1): Descending process of jugal present 4 uppers, 4 lowers), a condition occurring and hooking posteriorly. The bone frag- elsewhere among xenarthrans only in ment floating in isolation just lateral to the 16 AMERICAN MUSEUM NOVITATES NO. 3536

base of the coronoid process in SGO PV it was, given the trilobate cheek teeth of 2995 (see description) indicates that a des- glyptodontids, are such teeth primitive for cending process with this orientation was dasypodids and/or xenarthrans as a whole, likely present in Pseudoglyptodon. with subsequent loss several times indepen- dently? Given the poorly resolved phylogenet- ic placement of glyptodontids relative to other CONCLUSIONS cingulates, the possible transformation history of the dentition in early xenarthrans is New material referable to Pseudoglyptodon currently not readily optimized. Unless glyp- from the Andean Main Range of Chile offers todontids can convincingly be shown to di- tantalizing new evidence about character verge basal to all other cingulates, the trilobed evolution in the early history of Phyllophaga. cheek teeth in Pseudoglyptodon are likely The Chilean taxon exhibits several diagnostic convergent upon those in glyptodontids features previously seen only in sloths; never- (which lack the reduced number of teeth theless, its retention of at least one primitive characterizing phyllophagans). Thus, it is also attribute argues for its divergence prior to the possible that simple ovoid teeth characterized appearance of the common ancestor that gave phyllophagans (and tardigrades) ancestrally, rise to Bradypus and Choloepus plus all its with Pseudoglyptodon, orophodonts, and glyp- descendants. SGO PV 2995, the holotype of P. todontids each developing more complex chilensis, is regrettable for all the phylogenet- cheek teeth independently. ically important information it might have Finally, in view of the many derived revealed were it not for the violent, and likely resemblances between Pseudoglyptodon and hot, conditions prevailing during the skull’s glypodonts, a word about the possible re- volcanically associated deposition. The thinner lationship of these two groups is in order. areas of the specimen (most of the back end of Might Pseudoglyptodon be an early-diverging, the skull and basicranium, posteroventral re- peculiarly specialized glyptodont, rather than gion of the mandible, and zygomatic arch) were a phyllophagan? It is conceivable, after all, likely incinerated during burial. that the resemblances noted between Pseudo- The remains of pseudoglyptodontids are glyptodon and glyptodonts reflect a unique extremely rare: of the hundreds of mammal common ancestry—in which case there is specimens collected at Tinguiririca, only two either a great deal of convergence between are referable to Pseudoglyptodon. Further- this glyptodontoid clade and tardigrades, or more, we have recovered no specimens refer- the unusual features common to Pseudo- able to the group from the dozens of other glyptodon, glyptodontids, and tardigrades Cenozoic mammal localities recently uncov- represent ancestral conditions for Xenarthra. ered across a ,500-km-long swath of the Acceptance of an exclusive Pseudoglyptodon– Andean Main Range. Given the scarcity of glyptodont relationship would imply that reported specimens, the group was uncommon Pseudoglyptodon diverged from other mem- in higher (Patagonia, Argentina) and lower bers of the clade prior to the origin of the (Salla, Bolivia) latitudes as well. central dentine figure, and potentially before Pseudoglyptodontids complicate what the appearance of osteoderms (assuming would otherwise be a fairly straightforward Pseudoglyptodon truly lacked them). While picture of dental evolution in the early di- intriguing, pending a clearer understanding versification of xenarthrans (teeth reduced to of the phylogenetic placement of glyptodonts simple, peglike structures in early xenarthrans, relative to other cingulates, we regard this with the number of these primitively simple alternative as currently less viable than teeth greatly reduced in phyllophagans). the hypothesized tardigrade affinities of Inasmuch as the nearest known outgroup to Pseudoglyptodon favored above. tardigrades is characterized by trilobed cheek teeth, a number of more complex scenarios ABBREVIATIONS must now be entertained. Was, as Engelmann (1987) suggested, the ancestral tardigrade AMNH American Museum of Natural dentition marked by lobate postcanines? If History 2006 MCKENNA ET AL.: PALEOGENE PSEUDOGLYPTODONT XENARTHRANS 17

MLP Museo de La Plata Anonymous 1985. Termas del Flaco Quadrangle, PU Princeton University 1 : 50,000 topographic sheet. Instituto SGO PV Museo Nacional de Historia Natural, Geogra´phico Militar de Chile 3445–7015. Santiago, Chile, vertebrate paleontol- Castellanos, A. 1932. Nuevos ge´neros de glypto- ogy collections dontes en relacio´n con su filogenia. Physis (Revista de la Sociedad Argentina de Ciencias ACKNOWLEDGMENTS Naturales) 11: 92–100. Charrier, R., A.R. Wyss, J.J. Flynn, C.C. Swisher III, M.A. Norell, F. Zapatta, M.C. McKenna, We thank the National Geographic Society and M.J. Novacek. 1996. New evidence for late for support of the initial field season, the Mesozoic–early Cenozoic evolution of the National Science Foundation, and the Eppley Chilean Andes in the upper Tinguiririca Foundation. Reynaldo Charrier freely shared Valley (35uS), central Chile. Journal of South his geologic expertise and has enthusiastically American Earth Sciences 9(5/6): 393–422. embraced mammal fossils for deciphering de Queiroz, K., and J. Gauthier. 1990. Phylogeny as Andean geochronology. We thank the reverse a central principle in taxonomy: phylogenetic fault in the upper reaches of the Rı´o definitions of taxon names. Systematic Zoology Tinguiririca, for without it there would be no 39: 307–322. Engelmann, G.F. 1987. A new Deseadan sloth Termas del Flaco, without which there would (Mammalia: Xenarthra) from Salla, Bolivia, have been no economic rationale for a road so and its implications for the primitive condition deep into the Andean Main Range, without of the dentition in edentates. Journal of which the paleontological riches of the Vertebrate Paleontology 7(2): 217–223, figs. 1, 2. Abanico Formation might not have come to Flynn, J.J., M.A. Norell, C.C. Swisher III, and A.R. light for another century. Our work has had Wyss. 1991. Pre-Deseadan, post-Mustersan the long-term backing of the Museo Nacional mammals from central Chile: an update. de Historia Natural and the Consejo de Journal of Vertebrate Paleontology 11 Monumentos Nacionales, Santiago, Chile. (suppl. to 3): 29A. Daniel Frassinetti and Marı´a Eliana Ramı´rez Flynn, J.J., A.R. Wyss, D.A. Croft, and R. Charrier. 2003. The Tinguiririca fauna, Chile: have been pivotal in this regard. Gasto´n biochronology, biogeography, paleoecology, Mancilla provided access to land producing and a new earliest Oligocene South American part of the Tinguiririca Fauna. Susan Bell Land Mammal ‘Age’. Palaeogeography, Pa- provided invaluable assistance with locality laeoclimatology, Palaeoecology 195: 229–259. and specimen data. Chester Tarka produced Gaudin, T.J. 2004. Phylogenetic relationships among the photograph making up figure 3. Timothy sloths (Mammalia, Xenarthra, Tardigrada): the Rowe was generous beyond the call of duty in craniodental evidence. Zoological Journal of the facilitating the CT scanning, without which Linnean Society 140(2): 255–305. ´ our description would be far less complete. Grasse´, P.-P. 1955. Ordre des Edente´s. In P.-P. The comments of George Engelmann and Grasse´ (editor), Traite´ de Zoologie, vol. 17, Mammife`res: 1182–1266. Paris: Masson. those of a highly insightful anonymous re- Hoffstetter, R. 1958. Xenarthra. In J. Piveteau viewer improved the manuscript substantially. (director), Traite´ de Pale´ontologie, tome VI, vol. 2: 535–636, figs. 1–64. Paris: Masson. REFERENCES Kay, R.F., R.H. Madden, M.G. Vucetich, A.A. Carlini, M.M. Mazzoni, G.H. Re, M. Heizler, Ameghino, F. 1897. Mammife`res cre´tace´s de and H. Sandeman. 1999. Revised geochronol- l’Argentine. (Deuxie`me contribution a` la con- ogy of the Casamayoran South American Land naissance de la faune mammalogique des Mammal Age: climatic and biotic implications. couches a` Pyrotherium.) Boletı´n del Instituto Proceedings of the National Academy of Geogra´fico Argentino, Buenos Aires, 18: Sciences (U.S.) 96(23): 13235–13240. 406–429, 431–521 (also issued as separate, 117 Klohn, C. 1960. Geologı´a de la Cordillera de los pp.). Andes de Chile Central; provincias de Ameghino, F. 1902. Notices pre´liminaires sur des Santiago, O’Higgins, Colchagua y Curico´. mammife`res nouveaux des terrains cre´tace´s de Instituto de Investigaciones Geole´ogicas. Patagonie. Boletin de la Academia Nacional de Boletı´n 8: 1–95. Ciencias de Co´rdoba 17: 5–70 (3–68 in the MacFadden, B.J., K.E. Campbell, Jr., R.L. Cifelli, separates), 3 unnumbered text figures. O. Siles, N.M. Johnson, C.W. Naeser, and P.K. 18 AMERICAN MUSEUM NOVITATES NO. 3536

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