Megatherium Altiplanicum N

Home , Megatheriidae

The smallest and most ancient representative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), from the Pliocene of the Bolivian Altiplano

Pierre-Antoine SAINT-ANDRÉ Laboratoire de Paléontologie, Muséum national d’Histoire naturelle, 8 rue Buffon, F-75231 Paris cedex 05 (France)

Gerardo DE IULIIS Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario, M5S 3G5 (Canada) Faculty of Community Services and Health Sciences, George Brown College, 200 King Street East, Toronto, Ontario, M5A 1J5 (Canada) [email protected]

Saint-André P.-A. & De Iuliis G. 2001. — The smallest and most ancient representative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), from the Pliocene of the Bolivian Altiplano. Geodiversitas 23 (4) : 625-645.

ABSTRACT A new species of Megatherium Cuvier, 1796, M. altiplanicum n. sp., from the Montehermosan (Pliocene) of the north central Altiplano of Bolivia is described. It represents the earliest and smallest species of its genus and is the sister species of Megatherium americanum Cuvier, 1796 based on the following synapomorphies: very deep horizontal ramus of the dentary, prominent torsion of the femoral diaphysis, relatively concave medial and lateral femoral margins, and reduced patellar trochlea. The premaxillae are derived in being fused to each other and the maxilla, and relatively robust, features shared with M. americanum and M. tarijense Gervais & Ameghino, 1880, but those of M. americanum are more robust and quadrangular. In size, the new species resembles Eremotherium sefvei De Iuliis & Saint-André, 1997, but in the latter the femoral diaphysis is moderately twisted, the femoral margins are more nearly rectilinear, and the patellar trochlea unreduced. The presence of the new species in the Montehermosan suggests that the genus Megatherium had emerged by the beginning of the Pliocene, and that the most recent common KEY WORDS ancestor of the clade (including also M. americanum and M. tarijense), Xenarthra, Megatheriidae, predates the Pliocene. Megatherium was apparently adapted to a temperate Megatherium, climate, as opposed to the more tropical range occupied by Eremotherium Pliocene, Spillmann, 1948. The discovery of the new species possibly indicates broad Bolivia, Montehermosan, ecological similarity between the Pliocene Altiplano and the Argentinian new species. lowlands, and that the clade may have originated on the Altiplano.

GEODIVERSITAS • 2001 • 23 (4) © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. www.mnhn.fr/publication/ 625 Saint-André P.-A. & De Iuliis G.

RÉSUMÉ Le plus petit et le plus ancien représentant du genre Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), du Pliocène de l’Altiplano bolivien. Une nouvelle espèce de Megatherium Cuvier, 1796, M. altiplanicum n. sp., datant du Montehermoséen (Pliocène) et venant du centre-nord de l’Altiplano de Bolivie est décrite ci-après. Cette espèce représente la plus ancienne et la plus petite des espèces de son genre et, selon les caractères synapomorphiques sui- vants, serait l’espèce sœur de Megatherium americanum Cuvier, 1796 : un rameau mandibulaire horizontal très profond, une diaphyse fémorale présen- tant une torsion proéminante, des marges fémorales médianes et latérales relati- vement concaves et un trochléaire patellin réduit. La fusion des prémaxillaires entre eux et avec la maxillaire, indicatif d’un caractère dérivé, ainsi que la robus- tesse relative de ceux-ci, sont caractéristiques également de M. americanum et de M. tarijense Gervais & Ameghino, 1880, bien que les prémaxillaires de M. americanum soient plus robustes et quadrangulaires. Cette nouvelle espèce ressemble à Eremotherium sefvei De Iuliis & Saint-André, 1997 en taille mais ce dernier a une diaphyse fémorale modérément tordue, des marges fémorales presque rectilignes et un trochléaire patellin qui n’est pas réduit. La présence de cette nouvelle espèce datant du Montehermoséen suggère que le genre Megatherium émergea dès la début du Pliocène et que l’ancêtre commun le plus MOTS CLÉS récent de ce clade (incluant M. americanum et M. tarijense) précède le Pliocène. Xenarthra, Apparemment, Megatherium était adapté à un climat tempéré, contrairement à Megatheriidae, Megatherium, Eremotherium Spillmann, 1948 qui lui, se retrouve en régions plus tropicales. Pliocène, La découverte de cette nouvelle espèce indique la possibilité de similarités éco- Bolivie, Montehermoséen, logiques entre l’Altiplano du Pliocène et les basses terres de l’Argentine et que le nouvelle espèce. clade est peut-être originaire de l’Altiplano.

INTRODUCTION and, with a femur 390 mm in length, smaller in size than other species traditionally assigned to The genus Megatherium is known mainly from Megatherium. Other remains from Pomata (Bolivia) the giant ground sloth M. americanum described were assigned to this species. Hoffstetter (1986) by Cuvier (1796). M. gallardoi Ameghino & believed that it was possibly ancestral to Kraglievich, 1921 is a second large species, but is Megatherium. poorly known. Other species of the genus, such The new species Megatherium altiplanicum n. sp. as M. medinae Philippi, 1893, M. istilarti is based on remains from Ayo Ayo-Viscachani and Kraglievich, 1925 and M. tarijense Gervais & Pomata. It is the smallest and earliest species of its Ameghino, 1880 (see Boule & Thévenin 1920), genus. This combination of size and age reflects are smaller, although still large mammals. All the increase of body size over time, which is one of these species are of Pleistocene age. The discovery the more important evolutionary trends among of a small species of Megatherium from the megatheriines. The medial length of the femur is Pliocene of the Bolivian Altiplano is important comparable to that of Eremotherium sefvei De phylogenetically and paleoecologically. Iuliis & Saint-André, 1997, a small species from In discussing the Ayo Ayo (Bolivia) fauna, the Bolivian Pleistocene. However, the lateral Hoffstetter et al. (1971) reported the discovery femoral length is shorter than the medial, whereas from Pliocene beds of a megatheriine species that this condition is reversed in E. sefvei. These species is more similar to Megatherium than to the in- are clearly distinguished on the forms of the tertropical genus Eremotherium Spillmann, 1948 femoral diaphysis and the patellar trochlea

626 GEODIVERSITAS • 2001 • 23 (4) The smallest and most ancient Megatherium (Tardigrada, Megatheriidae)

(cf. infra). M. altiplanicum n. sp. is considerably smaller than the supposed Montehermosan species

M. gaudryi Moreno, 1888 from the Monte Lake Titicaca Hermoso region of Buenos Aires Province, Argentina. Its systematic position with respect to La Paz several other poorly known taxa, such as PERU Promegatherium Ameghino, 1883 and M. anti- quum Ameghino, 1885 is unclear. Better collections 1 BOLIVIA 2 Cochabamba of these taxa, with precise stratigraphic controls, are required before such questions may be addressed. Oruro

CHILE 3 ABBREVIATIONS Lake Poopó IFEA Institut français d’Études andines, Lima; FMNH Field Museum of Natural History, Chicago; MACN Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires; VENEZUELA MLP Museo de La Plata, La Plata; COLOMBIA MNHN Muséum national d’Histoire naturelle, EQUADOR

PERU Paris (MNHN is followed by AYO or BOLIVIA

POM, denoting that the specimen is BRAZIL from Ayo Ayo or Pomata, respectively); MNHN BOL Museo Nacional de Historia Natural, PARAGUAY La Paz; ROM Royal Ontario Museum, Toronto; CHILE

URUGUAY M upper molariform; ARGENTINA m lower molariform.

FIG. 1. — Map showing the geographical positions of the Ayo Ayo-Viscachani and Pomata localities yielding remains of SYSTEMATICS Megatherium altiplanicum n. sp. 1, Ayo Ayo; 2, Viscachani; 3, Pomata. Infraorder TARDIGRADA Latham & Davies in Forster, 1795 TYPE STRATA. — The Ayo Ayo-Viscachani fossiliferous locality (Fig. 1) lies in the upper part of the Umala Family MEGATHERIIDAE Gray, 1821 Formation. Subfamily MEGATHERIINAE Gray, 1821 ETYMOLOGY.— altiplanicum: neoformed Latin adjec- Genus Megatherium Cuvier, 1796 tive (altiplanicus, -a, -um) meaning “relative to the Megatherium altiplanicum n. sp. Altiplano, from the Altiplano”, commemorating that the holotype and referred specimens derive from the HYPODIGM. — Holotype (MNHN AYO 101); this Bolivian Altiplano. specimen preserves the palate, including both alveolar REFERRED SPECIMENS. — From Ayo Ayo: series, the maxillae anteriorly to the anterior root of the Departamento La Paz, 17°05’S, 68°00’W: distal end zygomatic arch; the horizontal ramus, angular process of a left femur (MNHN AYO 105); right cuneiform and part of the condyle of the left dentary; fragments of (MNHN AYO 150); left radius (MNHN AYO 203); the horizontal and ascending rami, with parts of the premaxillae of a juvenile individual (MNHN AYO coronoid process and condyle, of the left dentary; the 230); proximal half of a right ulna (MNHN BOL V atlas; two consecutive thoracic vertebrae and the neural 3304); right navicular (MNHN BOL V 3312). arch of the next thoracic vertebra; the neural arches of From Viscachani: Departamento La Paz, approximate- three lumbar vertebrae; four consecutive caudal verte- ly 17°09’S, 68°50’W: distal part of a left humerus brae; the proximal part of the right ulna; the left femur. (MNHN BOL V 3338). TYPE LOCALITY. — The type specimen was recovered From Pomata: Departamento Oruro, 18°20’S, from near Ayo Ayo, Departamento La Paz, 17°05’S, 67°55’W: atlas (MNHN POM 57); posterior part of a 68°00’W, a village on the Altiplano. The fossiliferous right dentary, including angular process and condyle locality is approximately 1 km south of Ayo Ayo. (MNHN BOL V 3294).

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Years South American North Central Epochs (Ma) Land Mammal Age Altiplano

Lujanian 0.5 Pleistocene Ensenadan 1.5 Ulloma Fm 1.6 Marplatan

2.5 Chapadmalalan Pliocene 2.8 Toba Ayo Ayo B

Umala Fm Montehermosan 5.3 A 5.4 Toba 76 6 Pomata Fm

Huayquerian Miocene

Rosa Pata Fm 12 Group Tortora

Chasicoan

FIG. 2. — Diagram showing chronostratigraphy of South American Land Mammal Ages and position of the Pomata (A), and Ayo Ayo- Viscachani (B) localities (modified after Marshall & Sempéré 1991).

Fossils in MNHN were collected by Robert the head and distal condyles, lateral margin forming a Hoffstetter in 1976. The type specimen was recovered sigmoid curve, and patellar trochlea reduced to the from an area sufficiently restricted in size to permit its lateral half of the distal end of the femur, but appar- attribution to a single individual. Fossils in MNHN ently not to the degree as occurs in M. americanum. BOL were collected during collaborative field seasons between this institution and IFEA. GEOLOGY DIAGNOSIS. — Much smaller than M. americanum, The Umala Formation is bounded by the Toba and smaller also than M. medinae and M. tarijense. 76 and Ayo Ayo volcanic tuffs, which lie at its Ventral bulge of dentary relatively as deep as in M. americanum. Premaxillae firmly fused to each other base and top, respectively (Fig. 2). Radiometric and to maxillae, but less robust than in M. ameri- analyses of various minerals (i.e. biotite, sanidine) canum. Palate narrows anterior to M1. Angular date the Toba 76 tuff at approximately 5.4 Ma, process distinct and more pointed than in M. ameri- and the Ayo Ayo tuff at approximately 2.8 Ma, canum; posterior part of the symphysis extends to the plane passing through m1. Femur twisted, with greater which indicate that the Umala Formation is of trochanter lying posterior to the plane passing through early and middle Pliocene age, according to the

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FIG. 3. — Skull remains of Megatherium altiplanicum n. sp.; A-C, premaxillae of a juvenile individual (MNHN AYO 230); A, proximal view; B, ventral view; C, left lateral view; D, E, partial premaxillae and maxillae, holotype (MNHN AYO 101); D, occlusal view; E, right lateral view. Scale bar: 5 cm. chronology of Marshall et al. (1992). M. alti- Huayquerian age (“Conglomerado Pomata” of planicum n. sp. belongs to the Montehermosan Marshall & Sempéré 1992), and above a volcanic Land Mammal Age. tuff which probably represents a horizontal The Pomata fossiliferous deposits (Fig. 1) were extension of the Toba 76 from the base of the initially referred to the Mauri Formation by Paz Umala Formation. et al. (1966), but they are probably unrelated stratigraphically and ecologically to the Mauri DESCRIPTION Formation from the Oligocene and Miocene of Skull the western Cordillera and western Altiplano. The type skull material (Fig. 3) preserves the The Pomata locality lies above the conglomeratic maxillae and premaxillae incompletely, and the facies of the Rosa Pata Formation, which is of right M1-M3 and left M1. Measurements are

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TABLE 1. — Measurements (mm) of skull and mandible of by a very flattened elliptical space. Anteriorly nar- Megatherium altiplanicum n. sp., holotype (MNHN AYO 101). row, they widen progressively posteriorly, apparently following a constant radial curve. They are Minimum palatal width Between L and R M1 28.9 not rectangular, in contrast to the condition in Between L and R M2 24.0 adult individuals of M. americanum. The triangu- Between L and R M3 28.2 lar condition, however, occurs in juvenile of the Between L and R M4 30.0 Midline palatal length, 143.0 latter species (e.g., MACN 2830). level of M1 to choanae In M. altiplanicum n. sp. the ventral margin of Maximum height horizontal 145.0 the premaxilla is nearly flat in lateral view. The ramus of dentary Toothrow length between M1-M3 94.7 anterior third of the dorsal margin is dorsoven- Lower toothrow length, alveolar 143.6 trally narrow; the central third rises at an angle of Maximum length and width of molariforms nearly 20°; the posterior third inclines slightly M1 31.6; 29.1 posteriorly. The dorsal surface bears a very obtuse M2 30.9; 36.4 M3 31.6; 35.0 angle between the posterior third and anterior m1 27.3; c. 34 two thirds. The posterior margin of the articulat- m2 32.7; 34.0 ed premaxillae is trapezoidal, with base ventral. m3 32.4; 30.0 m4 32.7; 25.5 The posterior surface of each premaxilla bears three processes, which were probably received by corresponding depressions in the maxilla. A ven- given in Table 1. Laterally the right maxilla tromedial process joins that from the other pre- includes the anterior root of the zygomatic arch to maxilla to form a ventrosagittal protuberance. A the level of the buccal wall of the M1 alveolus. A second process lies ventrolaterally. A third lies at smaller portion of the left maxilla is preserved to the posterior extremity of the dorsolateral margin the level of the anterior root of the arch. of the premaxilla. Premaxilla. The width across the premaxillae Maxilla. In M. altiplanicum n. sp. the anterior posteroventrally is comparable to the palatal margin of the anterior zygomatic root is level interalveolar width (i.e. less than the width across with a transverse plane passing through the mid- the molariforms), which reflects the narrowed dle of M1, as occurs in E. laurillardi (Cartelle & maxillae anterior to M1. Two large palatine fis- De Iuliis 1995), although it may lie opposite the sures lie between and anterior to the M1s, septum between M1 and M2 in the latter; in approximately at the level where the palate nar- Megatheridium annectens Cabrera, 1928, it reach- rows. The premaxillae are fused firmly to the es the mesial surface of M1. The root lies more maxillae. Their anterior portions are missing as posteriorly in M. americanum, in which its posi- they are broken a short distance anterior to the tion varies from the septum between M1 and M2 palatine fissures in MNHN AYO 101. Based on to the distal part of M2. Apparently, the position the preserved proximal portions, the premaxillae is similar in M. medinae. do not narrow abruptly anteriorly, which is also In ventral view the antemolariform region of the the condition in M. americanum, but not in maxillar palate more closely resembles that in Eremotherium laurillardi (Lund, 1842) and prob- E. laurillardi, M. medinae and M. gallardoi, ably most other megatheriines (De Iuliis 1994). although to a lesser degree in the latter due to the The complete premaxillae of a juvenile individual brevity of this region, than in M. americanum (MNHN AYO 230; Fig. 3A, B) are unfused (Ameghino & Kraglievich 1921; Cabrera 1928; along their contact in the sagittal plane. In ven- Hoffstetter 1952). In the first two species and tral view, each premaxilla is triangular, somewhat M. altiplanicum n. sp., the antemolariform part elongated, and the anterior extremity is almost of the maxillar palate is nearly as wide as the imperceptibly widened. The distal, subterminal interalveolar width. Its lateral margins, between sagittal margins of the premaxillae are separated M1 and the premaxillae, are formed by « deux

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arêtes latérales qui se placent respectivement dans of the mesial crest is more prominent than the le prolongement de l’axe de chaque série distal facet of the distal crest. This also occurs in dentaire », a condition considered primitive by M3. The transverse crests of this molariform are Hoffstetter (1952: 60). In M. americanum and nearly equal in transverse width. The crests of M. parodii Hoffstetter, 1949, as well as in M2 and M3 are nearly rectilinear, but slightly Plesiomegatherium halmyronomum Cabrera, convex mesially. 1928, the antemolariform width of the maxillar Dentary. The dentary of M. altiplanicum n. sp. is palate is nearly equal to that between the buccal incompletely known. The holotype (Figs 4; 5) margins of the toothrows. preserves a right horizontal ramus, including In M. altiplanicum n. sp., the palate is narrow right and left symphyseal regions as far as the between the toothrows, and its width is less mesial wall of the left m1 alveolus; a medial frag- than the transverse width of M1-M3, which is ment of the right condyle; the right angular more similar to the condition in M. ameri- process; a lateral fragment of the alveolar region canum, M. medinae, and Pyramiodontherium of the left horizontal ramus, including part of the bergi (Moreno & Mercerat, 1891) than in anterior margin of the ascending ramus; a frag- E. laurillardi, Plesiomegatherium halmyronomum ment of the ventral margin of the left horizontal Cabrera, 1928 and Megatheridium annectens. In ramus; and part of the left coronoid process, these last three, the palate width is about equal including the condyle. to or wider than the width of the largest molar- The symphysis ends posteriorly at the level of iform. the distal margin of m1. As in all megatheri- The palatine fissures lie between the premaxillo- ines, the symphysis forms a trough-like spout. maxillary suture, approximately at the level where In dorsal view the lateral margins of the spout the premaxillae begin to narrow. Each fissure are parallel and extend anteriorly from the lin- forms a shallow depression; its floor is pierced by gual half of the mesial margin of the m1 alveo- a posterolateral foramen and a smaller, more lus; this morphology reflects a narrowing of the anterior foramen. lateral margin of the horizontal ramus. Further, Upper dentition. The upper molariforms the anterior margin of the spout is not recti- (Fig. 3D, E) resemble those of other megatheri- linear, but bears a distinct median notch. In ines. They are prismatic, quadrangular in section lateral view, the dorsal margin of the spout with width slightly exceeding length, and bear continues anteriorly from the alveolar margin, two transverse crests separated by a transverse, but is not rectilinear. Its proximal two fifths are V-shaped valley. concave, its distal three fifths slightly convex. A M1 is less triangular in cross section than that of mental foramen, representing the anterior emer- M. medinae and M. gallardoi (judging from the gence of the mandibular canal, lies on the alveoli in the latter; Ameghino & Kraglievich lateral surface of the central part of the spout. 1921). Indeed, it resembles the M1 of M. ameri- The canal continues posteriorly within the lin- canum (as illustrated, for example, by Owen gual wall of the dentary. It emerges posteriorly, 1856), which is nearly trapezoidal in section, facing anteriorly and dorsally, between m4 and with a wider distal surface and a slightly rounded the anterior margin of the ascending ramus. mesial surface. However, the shape of M1 varies The ventral margin of the dentary of M. alti- between nearly trapezoidal to triangular in both planicum n. sp. bulges prominently, with maximum M. americanum and E. laurillardi. The distal depth occurring beneath m3. The depth of the transverse crest is wider than the mesial, and its dentary relative to the toothrow length is nearly distal wear facet is considerably more prominent equal to that of M. americanum, in which depth than the mesial facet of the mesial crest. exceeds that of all other megatheriines The mesial crest of M2 is slightly shorter trans- (Kraglievich 1930; Hoffstetter 1952; Cartelle versely than the distal crest. The mesial wear facet 1992) due to increased hypsodonty. The ventral

GEODIVERSITAS • 2001 • 23 (4) 631 Saint-André P.-A. & De Iuliis G.

FIG. 4. — Dentary of Megatherium altiplanicum n. sp., holotype (MNHN AYO 101), partial right and left dentaries; A, right lateral view; B, occlusal view; C, left lateral view. Scale bar: 5 cm.

margin of the dentary of M. lundi seijoi low convexity, lying parallel to the posteroventral (Kraglievich 1931: figs 1, 2) is more gently margin of the angular process, reflects the depth curved between the anterior extremity of the of the fossa. spout and apex of the mandibular bulge. The post-molariform part of the dentary is more MNHN AYO 101 (Fig. 5A, B) reveals that the completely preserved in MNHN BOL V 3294 angular process of M. altiplanicum n. sp. is more (Fig. 5C, D). It also indicates that the angular prominent, with dorsal and ventral margins near- process and insertion for the medial pterygoid ly parallel, than the relatively short and stout were more prominent and deeper, respectively, process of M. americanum. The medial surface of than in M. americanum. The anterior margin of the angular region bears a well-developed fossa the ascending ramus rises almost vertically lateral for insertion of the medial pterygoid muscle. A to the distal part of m4, and in lateral view covers

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FIG. 5. — Posterior part of dentary of Megatherium altiplanicum n. sp., lateral views of A, right angular process and B, left condyle and coronoid process of holotype (MNHN AYO 101); and C, lateral and D, medial views of right angular region and condyle of MNHN BOL 3294. Scale bar: 5 cm.

part of this tooth, as occurs in M. americanum, gins, although parts of m1 and m2 are preserved M. medinae and M. sundti Philippi, 1893. In above the margins. The molariforms are quad- E. laurillardi, however, the anterior margin rangular in section. The transverse axis of m1 lies inclines slightly posteriorly and most of m4 is obliquely, from mesiolingual to distobuccal, to visible in lateral view (Hoffstetter 1952). the longitudinal axis of the dentary. m2 is The condyle resembles that of M. americanum. mesiodistally shorter buccally than lingually, and Its articular surface is transversely elongated and its mesial surface is parallel to the distal surface of convex. Its medial half is rounded, approximately m1. The mesial and distal surfaces of m3 are semicircular, and its lateral half is nearly elliptical slightly convex, and more nearly perpendicular to and connected to the lateral surface of the the longitudinal axis of the horizontal ramus than ascending ramus by a poorly defined crest. those of m1 and m2. The mesial surface of m4 is Lower dentition. All molariforms (Fig. 4A, B) shorter than the distal surface of m3, and slightly are broken below the level of the alveolar mar- more convex. Its buccal and lingual surfaces con-

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verge distally. The distal surface of m4 of vertebral foramen) is a short, transverse canal, MNHN AYO 101 has suffered considerable which passes into the neural canal. The alar fora- damage, but the alveolar wall of m4 of MNHN men passes dorsoventrally through the anterome- BOL V 3294 is very rounded. As in M. lundi sei- dial part of the wing. Whereas the alar and joi (Kraglievich 1931), m1 and m2 are implanted transverse foramina (although better described as obliquely in the dentary, and incline posteriorly, canals) become confluent within the lateral mass but m4 is vertical. of the atlas and emerge ventrally upon the atlantal fossa through a common opening in Axial Skeleton M. americanum, they remain separated in M. alti- Atlas. The altas of the holotype, missing only a planicum n. sp. Hoffstetter (1952) stated that the part of the right wing, differs in minor details atlas of E. laurillardi bore the normal four foram- from that of M. americanum. Measurements are ina: the alar, transverse, and the anterior and pos- given in Table 2. In anterior or posterior view terior intervertebrals, and apparently considered the neural canal is clearly more compressed this as being the normal condition in this species dorsoventrally than in the Pleistocene species, and M. americanum. However, the presence of and the ventral arch is proportionately much the posterior intervertebral is variable in E. lauril- wider mediolaterally but shorter anteroposteri- lardi (cf. ROM 4219) and M. altiplanicum n. sp., orly. Its neural surface bears the fovea dentis and presumably also in M. americanum. Such along its median length. In E. laurillardi the variation apparently also occurs in Megalonyx, fovea varies between occupying the whole and in some specimens the foramen is present length and the posterior two thirds of the ven- only on one side (McDonald 1977). tral arch. The ventral tubercle is poorly devel- The wing is proportionately much larger than in oped. In anterior view, the anterior articular M. americanum. Its dorsal surface bears a well- facets curve more strongly toward the mid-line. defined fossa or depression (probably for inser- The second intervertebral foramen, normally for tion of the recti capitis muscles) that extends the passage of blood vessels and the second cervi- anterior to the anterior intervertebral foramen to cal or spinal nerve, may be formed between the reach the level of the anterior margin of the dor- atlas anteriorly and the axis posteriorly. This sal arch. In M. americanum it does not extend occurs in MNHN AYO 101. In posterodorsal beyond the foramen. Further, the wing in view of the atlas, this passage forms a smooth, M. altiplanicum n. sp. is distinctly defined anteri- transverse trough between the root of the dorsal orly by an emargination, produced by a lateral arch and the anteromedial wall of the facet for the prolongation of the dorsolateral margin of the axis. The trough leads medially into the neural anterior articular facet, between the wing and the canal; laterally it is bounded by the medial margin facet. In M. americanum the margin of the wing of the transverse foramen. However, a second curves without interruption into the dorsolateral condition may occur, as in MNHN POM 57, margin of the articular facet. where the trough is enclosed by an osseous bridge As in M. americanum and other ground sloths, between the posterodorsal margin of the dorsal the atlas bears three separate articular facets for arch and the dorsomedial margin of the facet for the axis: two lateral; the third, median and ven- the axis. This short, transverse canal is similar to tral, articulates with the dens of the axis. The lat- the trough in arrangement, probably included the eral facets are contiguous ventrally with that for structures that passed between the interverbral the dens in E. laurillardi and E. eomigrans De foramen, and creates two additional foramina: Iuliis & Cartelle, 1999; this condition is apomor- one opening medially, and the second opening phic for Eremotherium (Cartelle 1992; De Iuliis laterally dorsal to the transverse foramen. & Cartelle 1999). Two other foramina are present in M. alti- Thoracic vertebrae. The holotype preserves two planicum n. sp. The intervertebral foramen (= lateral consecutive thoracic vertebrae and the dorsal arch

634 GEODIVERSITAS • 2001 • 23 (4) The smallest and most ancient Megatherium (Tardigrada, Megatheriidae)

of the following vertebra. A parapophyseal articu- Radius. The left radius (MNHN AYO 203; lar surface lies on the anterior surface of the base Fig. 6; Table 2) of M. altiplanicum n. sp. is small- of the dorsal arch of all preserved vertebrae. Their er than but morphologically similar to that of M. centra lack foveae costales. Thus the ribs of the americanum. It is also more gracile because its two complete vertebrae articulate only with the epiphyses are smaller compared to its length. parapophyses (i.e. they are syncephalic ribs). In Further, in anterior or posterior views the diaph- M. americanum this condition occurs only for the ysis is apparently narrower due to a shorter and last thoracic. This suggests that the complete ver- less prominent lateral crest, which served largely tebrae and the dorsal arch belong to the most for the insertion of the pronator teres. The crest is posterior part of the thoracic series, and that in widest within the proximal subterminal quarter M. altiplanicum n. sp. vertebrae other than the of the radius; it lies further distally in M. ameri- final thoracic bear syncephalic ribs. canum. There is a pronounced angle between the The second complete thoracic vertebra bears sec- diaphyseal portions proximal and distal to the ondary or xenarthral postzygapophyses. The dor- crest in M. americanum and M. altiplanicum n. sal arch that follows bears parapophyses, and is sp., whereas in E. laurillardi, M. tarijense therefore a thoracic vertebra. Further, it bears (FMNH P14216) and M. medinae the angle xenarthral pre- and postzygapophyses. The between these portions is less abrupt. xenarthral condition thus is present in the poste- In M. altiplanicum n. sp. the diaphysis is marked- rior two of the three thoracic vertebrae. ly constricted mediolaterally between the crest Lumbar vertebrae. Two consecutive arches of and the distal end of the radius, and the lateral MNHN AYO 101 are very similar to those of and medial margins of this part of the diaphysis the lumbar vertebrae of M. americanum. They are subparallel, as occurs in M. americanum. In bear xenarthral pre- and postzygapophyses. The E. laurillardi, and apparently other megatheri- anterior of the two arches bears the intratrans- ines, the crest lies more distally still, near the versary foramen characteristic of the lumbar ver- midlength of the radius. Further, the diaphysis is tebrae of Xenarthra; the second arch is damaged constricted slightly just distal to the crest, but and does not permit recognition of the foramen. gradually widens distally. A distorted neural arch preserves its right postzy- The bicipital tuberosity lies more proximally in gapophysis, which articulates with the prezy- M. altiplanicum n. sp. and M. americanum than gapophysis of the anterior of the two arches. in E. laurillardi. In M. americanum it lies on the Caudal vertebrae. The four consecutive vertebrae medial surface of the radius, in the same trans- of the holotype resemble, based on the shape of verse plane as the lateral crest, whereas the their prominent transverse processes, caudal ver- tuberosity lies more posteriorly, approximately tebrae 1 to 6 of M. americanum. A poorly defined on the medioposterior radial surface in M. alti- tubercle lies sagitally on the anterior margin of planicum n. sp. the neural arch, anterior to the neural spine, of Ulna. The proximal part of the right ulna of the first of this series, and resembles in size and MNHN AYO 101 is preserved (Table 2). It is position those on caudal vertebrae 1 and 2 of smaller than that of M. americanum and varies M. americanum. The tubercle is absent in the morphologically in minor ways. The olecranon second vertebra of the series. Therefore, the ver- process is relatively smaller. The anconeal process tebrae of the holotype are probably caudal verte- is more prominent and distinct. Its margins meet brae 2 to 5. in an acute angle, whereas in M. americanum they Humerus. Only the distal end of a left humerus form an obtuse angle. (MNHN BOL 3338; Table 2) is known for M. Cuneiform. The cuneiform of megatheriines altiplanicum n. sp. It is smaller than that in M. articulates with the pisiform palmolaterally and americanum, and the epicondyles are less expand- the unciform distally. MNHN AYO 150 strongly ed and prominent relative to the trochlear surface. resembles that of M. americanum, but the facet

GEODIVERSITAS • 2001 • 23 (4) 635 Saint-André P.-A. & De Iuliis G.

AB CD

FIG. 6. — Right radius of Megatherium altiplanicum n. sp. (MNHN AYO 203); A, anterior view; B, posterior view; C, lateral view; D, medial view. Scale bar: 10 cm.

for the unciform is relatively larger, and that for head and the distal condyles, so that the bone the pisiform smaller (c. 30% of the maximum exhibits strong vertical torsion. In lateral view its width of the cuneiform, as compared to 38% in lateral margin is sigmoidal. This feature is also M. americanum). However, it is worth noting present in M. americanum (Hoffstetter 1952) and that Cartelle (1992) reported considerable varia- M. gallardoi (MACN 5002), but absent in tion in the shapes and relative sizes of the articu- Eremotherium, M. istilarti and M. medinae lar surfaces in E. laurillardi. (Kraglievich 1925a; Hoffstetter 1952). The last Femur. The medial length of the femur (Table 2) two species, therefore, are not properly considered of the holotype (Fig. 7) is nearly identical to that Megatherium sensu Hoffstetter (1952). As noted of the small species Eremotherium sefvei from the by De Iuliis & Saint-André (1997), torsion of the Pleistocene of Ulloma, Bolivia (387 mm; De femur is apparently due to a posterior displace- Iuliis & Saint-André 1997), which was probably ment of the greater trochanter: manipulation of very similar in body size (cf. infra) to M. altiplan- the elements of the hind limb that set the head, icum n. sp. greater trochanter, and medial distal condyle in The femur of M. altiplanicum n. sp. is smaller the same plane requires that the long axis of the than but similar to that of M. americanum. As in pes be oriented markedly anteromedially; whereas the latter, the greater trochanter projects markedly the pes is oriented anteroposteriorly when the posteriorly to the plane that passes through the head and distal condyles lie in the same plane.

636 GEODIVERSITAS • 2001 • 23 (4) The smallest and most ancient Megatherium (Tardigrada, Megatheriidae)

FIG. 7. — Left femur of Megatherium altiplanicum n. sp., holotype (MNHN AYO 101); A, anterior view; B, lateral view; C, distal view. Scale bar: 10 cm.

The greater trochanter rises slightly above the latter, the proximal and distal extremities are crest between the head and greater trochanter. markedly expanded transversely, the epicondyles The diameter of the neck is smaller than the max- prominent, and the lateral and medial margins imum diameter of the head, as in M. ameri- notably concave, whereas they are more nearly canum. The notch for the round ligament is rectilinear in E. laurillardi. In M. medinae the widely triangular, as in M. americanum and lateral margin is nearly rectilinear, a morphology E. laurillardi. It is narrow and elongated in diagnostic for the species (Casamiquela & E. sefvei and Pyramiodontherium bergi (MLP 2- Sepulveda 1974). The less concave margins are 66). probably plesiomorphic states. The femur of M. altiplanicum n. sp. is relatively The form of the medial condyle is diagnostic for narrower than that of M. americanum. As in the M. altiplanicum n. sp. It extends anterolaterally

GEODIVERSITAS • 2001 • 23 (4) 637 Saint-André P.-A. & De Iuliis G.

toward and approaches closely the patellar for M. americanum based on values obtained trochlea. These articular surfaces are in proximity from numerous allometric regressions of the den- in most megatheriines, but this is due to a tition, and cranial and postcranial elements. medially expanded patellar trochlea (e.g., E. lau- However, these authors obtained a more conser- rillardi), which is plesiomorphic. The patellar vative estimate of 4 000 kg by removing the effect trochlea of M. altiplanicum n. sp. is not medially of femur width (which clearly produces a dispro- expanded and thus resembles those of M. ameri- portionately high mass estimate in megatheres), a canum and M. gallardoi. In these latter species, value more similar to the mass obtained by other the medial articular surface and patellar trochlea authors (Casinos 1996). Using the allometric are widely separated, particularly in M. gallardoi equation obtained by Janis (1990) based on the (Kraglievich 1925b). Further, the trochlea does lower molar toothrow length of extant ungulates not project anteriorly in M. altiplanicum n. sp. gives a mass of 5 500 kg for M. americanum and and M. americanum, but does so in E. laurillardi 1 746 kg for M. altiplanicum n. sp. and E. sefvei. A second method for estimating mass, that of The patellar trochlea is contiguous with the arti- assuming geometric similitude between M. amer- cular surface of the lateral condyle, as in all icanum and M. altiplanicum n. sp., results in a megatheriines. In M. altiplanicum n. sp., these lower estimate. Using the specimen measured by surfaces are separated by a faint ridge. A similar Fariña et al. (1998) and a mass of 4 000 kg for ridge occurs in some specimens of M. ameri- M. americanum produces a mass of 977 kg for canum; a very weak, barely perceptible demarca- M. altiplanicum n. sp.; a mass of 6 000 kg for tion may be present in E. laurillardi (De Iuliis M. americanum produces a mass of 1 465 kg for 1996). M. altiplanicum n. sp. Navicular. A right navicular (MNHN BOL V This species is thus considerably smaller than 3312) from Ayo Ayo is referred to M. alti- M. americanum and M. gallardoi, and apprecia- planicum n. sp. It is smaller than that of M. ame- bly smaller also than M. medinae, M. istilarti, ricanum and the medial half of the astragalar M. gaudryi and M. tarijense (see Fig. 8). Indeed, facet is less concave. This part of the facet is it is one of the two smallest post-Miocene larger than the lateral, convex half, whereas megatheriines, the other being Eremotherium they are subequal in M. americanum. The sefvei from the Quaternary of Ulloma, Bolivia facets on the anterior surface are arranged as in (De Iuliis & Saint-André 1997). M. americanum, but the dorsomedial facet is The toothrow of M. altiplanicum n. sp. (see relatively smaller, and the ventral margin of the Fig. 9) is approximately one-third shorter than ventral facet is nearly rectilinear, compared to those of M. medinae and M. tarijense; these last the convex margin in the Pleistocene species. two species are similar in size (Casamiquela & As with the carpals, Cartelle (1992) reported Sepulveda 1974). Also, the mandibular toothrow considerable variation in the shapes and sizes of M. lundi sejoi (see Kraglievich 1931) is 39% of the articular surfaces of the tarsals in E. lau- longer than that of M. altiplanicum n. sp. rillardi. The anterior root of the zygomatic arch lies opposite M1, a position characteristic of the breviros- DISCUSSION tral (but see De Iuliis 1996) condition described The holotype of M. altiplanicum n. sp. represents by Cabrera (1928) based on the antemolariform an adult individual, which had thus attained its length of the maxilla in some megatheriines. In definitive size. Two methods for estimating mass brevirostral megatheriines, the length between the suggest that the mass of M. altiplanicum n. sp. mesial alveolar wall of M1 and the anterior may have been been approximately between one extremity of the maxilla is just below 17% of the quarter to one third that of M. americanum. condylomaxillar length, whereas in longirostral Fariña et al. (1998) calculated a mass of 6 000 kg megatheriines this ratio is approximately 20%. In

638 GEODIVERSITAS • 2001 • 23 (4) The smallest and most ancient Megatherium (Tardigrada, Megatheriidae)

350 280

300 240

250 200

Width (mm) 200

160 Mandibular height (mm) 150

100 120 300 400 500600 700 800 120 150200 240 280 Length (mm) Toothrow length (mm) M. altiplanicum M. medinae M. altiplanicum M. medinae M. tarijense ✕ M. americanum M. tarijense ✕ M. americanum

FIG. 8. — Plot of maximum length and midshaft width of the FIG. 9. — Plot of toothrow length and maximum mandibular femora of selected Megatherium species. Data for M. ameri- height of selected Megatherium species. Dashed line represents canum Cuvier, 1796, M. medinae Philippi, 1893 and M. tarijense a slope of 1. Data for M. americanum Cuvier, 1796, M. medinae Gervais & Ameghino, 1880 from De Iuliis (1996). Philippi, 1893 and M. tarijense Gervais & Ameghino, 1880 from De Iuliis (1996). the former group, the anterior root of the zygo- interalveolar width, whereas in M. americanum matic arch lies opposite the middle or distal part the prealveolar portion is wider than the inter- of M1, while in the latter it lies at the level of M2. alveolar width. Also, the interalveolar width is Cabrera (1928) and Paula Couto (1979) stated narrower that the width of the largest molariform that divergence of brevirostral and longirostral in M. altiplanicum n. sp., M. americanum, megatheriines, represented respectively by M. medinae and Pyramiodontherium bergi, where- Megatheridium and Plesiomegatherium, had as it is equal to or wider than the widest molari- occurred by the late Miocene. However, a differ- form in E. laurillardi, Megatheridium annectens, ence of 3% in the ratio of antemolariform maxil- and Plesiomegatherium halmyrononum (Cabrera lar length to condylomaxillar length lies within 1928; Hoffstetter 1952). the range of individual variation in Eremotherium The femur is strongly twisted in M. americanum laurillardi (De Iuliis 1996). The position of the and M. altiplanicum n. sp., as is clearly indicated anterior root of the zygomatic arch lies more pos- by the markedly sigmoidal curve of the lateral teriorly (i.e. approximately opposite M2) in most femoral margin. Hoffstetter (1952) considered megatheriines. However, the polarity of this char- this feature characteristic of Megatherium. The acter is equivocal, but it is worth noting that the femur is more nearly flat and its lateral margin root lies in the more posterior position in nearly rectilinear in Eremotherium, Plesio- Megathericulus, which is probably the sister taxon megatherium and M. medinae. This morphology to all other megatheriines, based on its highly is generalized and plesiomorphic for megatheri- mesiodistally compressed molariforms (De Iuliis ines, as compared to a femur that is strongly 1994). twisted and relatively constricted at its middle The palatal morphology of M. altiplanicum n. sp. (see De Iuliis & Saint-André 1997). resembles that of M. medinae and E. laurillardi in Casamiquela & Sepulveda (1974) considered that the prealveolar width is nearly equal to the Eremotherium to be merely a subgenus of

GEODIVERSITAS • 2001 • 23 (4) 639 Saint-André P.-A. & De Iuliis G.

TABLE 2. — Measurements (mm) of postracranial elements of M. medinae is occasionally referred to as the Megatherium altiplanicum n. sp. genus or subgenus Pseudomegatherium Kraglievich, 1931 (“false Megatherium”); e.g., by Hoffstetter Atlas (holotype, MNHN AYO 101) Maximum dorsoventral height 56.5 (1986), who stated that at least two as yet unde- Sagittal length of neural canal 24.0 scribed species could possibly be referred to Maximum dorsoventral height of neural canal 37.5 Pseudomegatherium, one from the Pleistocene of Maximum transverse width of neural canal 41.0 Dorsoventral height of glenoid fossa 40.0 Peru, the other from the Quaternary of Ecuador. Maximum length of wing 69.5 Casamiquela & Sepulveda (1974), followed by Width of wing, from neural canal 54.0 Hoffstetter (1986) and Marshall & Salinas to lateral margin (1991), synonymized M. sundti with M. medinae. Humerus (MNHN BOL V 3338) Maximum distal width 107.2 However, a femur of an immature individual Width of distal articular surface 70.6 (PIU M4530) from Ulloma, Bolivia, bears strong Radius (MNHN AYO 203) resemblance to that of M. americanum, except Maximum length 395.0 that the patellar trochlea is expanded medially. Maximum proximal diameter 52.5 Minimum proximal diameter 46.2 This medial expansion occurs in all other Maximum distal diameter 99.4 megatheriines for which the femur is known, Minimum distal diameter 61.2 except in M. americanum and M. altiplanicum Shaft width at level of lateral crest 67.0 Minimum transverse shaft width 42.0 n. sp. (De Iuliis & Saint-André 1997). Femur Minimum anteroposterior shaft thickness 27.4 PIU M4530 differs sufficiently in general mor- Ulna (MNHN BOL V 3304) phology from that of M. medinae to suggest that Olecranom process width 119.0 it belongs to a distinct species. De Iuliis & Saint- Olecranon process length, tuberosity 88.6 to anconeal process André (1997) noted that PIU M4530 probably Width of articular surface of trochlea 103.5 belonged to M. sundti, described from Ulloma by Femur (holotype, MHNH AYO 101) Philippi (1893), and thus considered this species Lateral length 379.0 Medial length 387.5 to be valid. It is worth noting here that Proximal width 203.1 Hoffstetter (1986: 224) reported the presence of Minimum shaft width 135.0 two megatheriine species from Plio-Pleistocene Maximum diameter of head 94.0 Maximum width between distal tuberosities 196.5 high Andean mammalian faunas as “M. sundti = Maximum width between condyles 140.0 synonym of M. americanum Cuvier?” However, Width of patellar trochlea 52.5 this passage is misprinted from Hoffstetter’s Maximum width of medial condyle 64.5 Maximum width of lateral condyle 77.0 manuscript for this article, and should read: and patellar trochlea “M. sundti Phil. = synonym of M.(Pseudo- Depth of medial condyle 85.0 megatherium) medinae Phil.; M. americanum Cuvier?” (Hoffstetter pers. comm. 1991).

PHYLOGENETIC RELATIONSHIPS Megatherium, with M. medinae being a transi- tional form between primitive species of The phylogenetic relationships among mega- Eremotherium sensu Hoffstetter (1952) and the theriines are not clearly understood, largely more derived species of Megatherium sensu because most described taxa are known only from Hoffstetter (1952). Although this view is proba- fragmentary remains. De Iuliis (1996) presented bly an oversimplification (De Iuliis 1996), the a strict consensus tree that recognized only a well-marked femoral torsion of M. altiplanicum basal megathere clade (Megathericulus and n. sp. avoids misidentification with M. medinae, Plesiomegatherium) and an unresolved crown which possesses the plesiomorphic femoral mor- group of eight taxa. Among the megatheriines phology (Kraglievich 1931; Hoffstetter 1986). discussed above, only Eremotherium laurillardi,

640 GEODIVERSITAS • 2001 • 23 (4) The smallest and most ancient Megatherium (Tardigrada, Megatheriidae)

Megatherium americanum, M. medinae and served. Strongly fused premaxillae are derived M. altiplanicum n. sp. are reasonably well known. (De Iuliis 1994, 1996). The premaxillae of The following characters permit a preliminary M. altiplanicum n. sp. are fused to each other and analysis of phylogenetic relationships among to the maxillae. As stated above, the premaxillae these four megatheriines. of M. medinae are unknown, but the maxillae bear deep articular pockets anterolaterally for the 1. DEPTH OF THE HORIZONTAL RAMUS premaxillae that are similar to those of E. lauril- OF THE DENTARY lardi. These observations indicate that the pre- The depth of the horizontal ramus of the dentary maxillae of M. medinae were only weakly sutured is important for determination of the evolution- to the maxillae, and probably each other, as ary relationships among megatheriines occurs in E. laurillardi. (Kraglievich 1930). The relative increase in depth of the jaw reflects increased hypsodonty; the 4. TORSION OF THE FEMUR index of mandibular height to toothrow length The femoral diaphyseal shaft of megatheriines is multiplied by 100 provides a measure of twisted so that the greater trochanter lies posteri- hypsodonty (Zetti 1964; De Iuliis 1996). In or to a plane passing through the head of the Eremotherium laurillardi, the values for this index femur and its distal condyles. The angle of tor- range between 66-83% and in M. americanum sion may be measured by placing the femur on a between 92-112%. The values for M. medinae table with the head, greater trochanter, and later- are intermediate between these. The value in al epicondyle in contact with the surface of the M. altiplanicum n. sp. is 101%, well within the table. This raises the distomedial part of the bone range for M. americanum. De Iuliis (1996) (De Iuliis & Saint-André 1997). The angle is ordered these states as follows: taken at the intersection between the surface of Index between 66-83%: plesiomorphic (0) the table, and a line passing through the antero- Index between 83-92%: apomorphic (1) posterior midpoints of the medial and lateral Index between 92-112%: apomorphic (2). condyles and extended to the table. The femur of E. laurillardi is moderately twisted, 2. SHAPE OF THE PREMAXILLA with values rarely surpassing 40°. The femur of De Iuliis (1994) demonstrated that the small, M. medinae is similar, but in M. americanum it is triangular, and plate-like premaxillae of E. lauril- markedly twisted. The greater trochanter projects lardi are plesiomorphic (state 0), whereas the more strongly posteriorly, and the angle of tor- elongated, quadrangular, and robust premaxillae sion is almost always greater than 40° (De Iuliis of M. americanum are derived (state 1). The pre- 1996; De Iuliis & Saint-André 1997). The mor- maxillae of M. altiplanicum n. sp. resemble those phology of the lateral margin of the femur is of M. americanum, but are somewhat less robust. correlated with the degree of torsion. In E. lauril- Those of M. medinae have not been recovered. lardi, the margin is nearly rectilinear. Hoffstetter (1952) stated that this character was also linked 3. SUTURAL ATTACHMENT OF THE PREMAXILLAE to the presence of a diagonal crest-like protuber- In E. laurillardi the premaxillae are only loosely ance extending from the greater trochanter to attached to each other and to the maxillae, so that the medial entepicondyle on the posterior and they are rarely recovered in situ. This condition is nearly flat surface of the femur, as occurs also in plesiomorphic (De Iuliis 1994, 1996). The pre- M. medinae, Paramegatherium incognitum (which maxillae of M. americanum are, in contrast, we regard as of questionable validity), and proba- strongly fused to each other and to the maxillae, bly M. istilarti. In M. americanum, the lateral and are almost always recovered in situ in adult margin of the femur is strongly sigmoidal (see De individuals. They are sometimes broken, but Iuliis & Saint-André 1997: fig. 6). De Iuliis small portions of their posterior ends are pre- (1996) noted that the moderately twisted femur

GEODIVERSITAS • 2001 • 23 (4) 641 Saint-André P.-A. & De Iuliis G.

with a nearly rectilinear lateral margin character- pronounced torsion of the femur, a femur with a istic of E. laurillardi is plesiomorphic (state 0); relatively constricted diaphysis and widened the strongly twisted femur with a sigmoidal later- proximal and distal ends, and reduction of the al margin of M. americanum derived (state 1). patellar trochlea. We consider it more prudent, M. medinae resembles E. laurillardi; M. altiplan- pending a thorough and comprehensive phyloge- icum n. sp. resembles M. americanum. netic analysis, to maintain the genus Megatherium as it has been used traditionally (i.e. 5. SHAPE OF THE MEDIAL AND LATERAL FEMORAL including M. medinae), rather than formally MARGINS recognize other possible generic names, such as In M. americanum and M. altiplanicum n. sp. the Pseudomegatherium. However, in order to middle part of the diaphysis is relatively more con- emphasize the sister species relationship between stricted than in E. laurillardi and M. medinae. The M. americanum and M. altiplanicum n. sp., we medial and lateral femoral margins in the first two assign the subgeneric name Megatherium to this species therefore are more concave, the femur is clade, as it contains the type species of the genus more robust, and the proximal and distal ends ap- (cf. ICZN 1999: art. 44.1). pear more prominent. In E. laurillardi and M. medinae, the diaphysis is relatively less constricted and the medial and lateral margins are ECOLOGICAL CONSIDERATIONS more nearly parallel. This condition, also present AND CONCLUSIONS in most other megatheriines, is plesiomorphic (state 0), that characteristic of M. americanum and The presence of M. altiplanicum n. sp. in the M. altiplanicum n. sp. is apomorphic (state 1; De Montehermosan of Bolivia indicates that a Iuliis 1996; De Iuliis & Saint-André 1997). megatheriine closely related to M. americanum has existed at least since the early Pliocene. M. altiplan- 6. DEVELOPMENT OF THE PATELLAR TROCHLEA icum n. sp. differs considerably from M. medinae, In E. laurillardi and M. medinae the patellar first described by Philippi (1893) from northern trochlea is well-developed and extends medially Chile, but to which have also been referred remains past the sagittal plane on the anterior surface of from the Quaternary of Bolivia (e.g., by the femur. This morphology occurs in nearly all Casamiquela & Sepulveda 1974; Marshall & other sloths, and De Iuliis (1996) and De Iuliis Salinas 1991). M. medinae is less derived than & Saint-André (1997) have shown that this con- M. altiplanicum n. sp. with respect to M. ameri- dition is plesiomorphic (state 0). The exceptions canum. It does not belong to Megatherium sensu are M. americanum, M. istilarti (see Kraglievich Hoffstetter (1952), but rather to the subgenus 1925b) and M. altiplanicum n. sp., in which the Pseudomegatherium, according to this author. trochlear facet is reduced and restricted to the Indeed, Hoffstetter (1986) followed Kraglievich middle lateral quarter of the anterior surface of (1931) who proposed Pseudomegatherium for the femur. This condition is derived (state 1). M. medinae. However, until a more comprehensive phylogenetic analysis is possible, we prefer to This brief analysis suggests that M. americanum, retain this species in Megatherium. M. altiplanicum n. sp., and M. medinae form a Casamiquela & Sepulveda (1974) suggested that clade, based on increased depth of the horizontal M. medinae is closely related to M. tarijense and M. ramus of the dentary and relatively robust pre- lundi. Further, they synonymized M. sundti, erect- maxillae that are fused to each other and the max- ed on damaged skulls from Ulloma by Philippi illae. Within this clade, M. americanum and (1893), with M. medinae. Consequently, these M. altiplanicum n. sp. are sister species, based on remains from the base of the Ulloma Formation, the following synapomorphies: a further increase Bolivia (i.e. early Lujanian) were referred to M. in depth of the dentary (Character 1, state 2), medinae. However, the remains (PIU M4530) dis-

642 GEODIVERSITAS • 2001 • 23 (4) The smallest and most ancient Megatherium (Tardigrada, Megatheriidae)

cussed above of an immature individual, suggest 1986). In contrast, Megatherium occurs in higher that M. medinae (with its plesiomorphic femur) latitudes (at low altitudes), and thus is probably does not occur in Ulloma. Probably, remains from characteristic of more temperate climates. The this region represent the species that Philippi presence of M. altiplanicum n. sp. in early and (1893) described as M. sundti. middle Pliocene sediments possibly indicates a It is apparent from the altitudinal and geographic broad ecological similarity between the Pliocene distribution of Megatherium sensu Hoffstetter Altiplano, on the one hand, and the Pleistocene (1952) (i.e. with a strongly twisted femur) that Altiplano and Argentinian lowlands, on the other. this genus was able to inhabit temperate lowlands As the oldest record of the genus occurs on the (M. americanum is known extensively from the Altiplano, it seems reasonable to assume that Quaternary pampas of Argentina), as well as high M. altiplanicum n. sp. evolved on the Altiplano altitudes as is indicated by the presence of and subsequently spread onto the central South M. altiplanicum n. sp. at Ayo Ayo-Viscachani American lowlands. Movement toward lower alti- during the Pliocene and M. sundti at Ulloma dur- tudes may have resulted from glaciations that, ing the Pleistocene. from at least 2.8 Ma (Patapatani Glaciation), oc- In Chile, M. medinae is known from Chiu-Chiu curred in the central Andes. However, the possi- (situated above 2 000 m) and in the western part bility exists that it immigrated to the Altiplano of the lowland Tamarugal Pampa. Casamiquela due to an ecological vacuum created by a massive & Sepulveda (1974) suggested that the occur- extinction (cf. infra). Such an extinction might rence of this species at such low altitude as the have been caused by the catastrophic deposition of Pampa was possibly caused by post-mortem trans- the volcanic tuff termed Toba 76 or possibly by a port. Various undescribed remains from central more global climatic change. and southern Peru apparently belong to a closely The megatheriine reported, along with a related form. Hoffstetter (1986) considered these mylodontid, from Member 6 of the Mauri remains to represent two species, distinguished Formation (Huayquerian) by Marshall et al. on the basis of size, and referred them to (1983) remains undescribed, and is not reported Pseudomegatherium based on the presence of a by Marshall & Sempéré (1992), who mention relatively flat femur. Fragmented remains from instead the presence of a mylodontid and a mega- the Puninian fauna of Ecuador were doubtfully lonychid. In any event, the presence of M. alti- assigned to this taxon, which is rare or absent in planicum n. sp. in the Montehermosan of the the northern Andes (Hoffstetter 1986). Altiplano is of itself of great paleobiogeographic Thus, the Megatherium species with a less twisted interest because it is the earliest certain species of femur apparently represent a series of Quaternary its genus (Montehermosan megatheriines from forms of uncertain monophyly that were adapted Argentina have usually been referred to to a high-altitude habitat in the central Andes. Plesiomegatherium, although doubtfully in some Importantly, increase in the depth of the dentary cases, as is indicated by “?Plesiomegatherium” in indicates that M. medinae (and perhaps other the faunal list for the Argentinian Monteher- species from the central Andes) is more closely mosan given by Marshall et al. 1983). M. medi- related to M. americanum and M. altiplanicum nae, considered Pliocene by earlier workers, was n. sp. than to E. laurillardi. The latter, also of assigned to the Pleistocene by Casamiquela & Quaternary age, extended from southern Brazil to Sepulveda (1974); remains from the base of the the southeastern United States (Cartelle & De Ulloma Formation are Lujanian (Marshall & Iuliis 1995). It is therefore generally considered to Salinas 1991) and probably belong to M. sundti. have been adapted to tropical regions, as well as a This indicates that the most recent common warm and dry climate. It is widespread east and ancestor of M. americanum, M. altiplanicum west of the Andes and enters some Andean valleys, n. sp., and M. medinae is at least early Pliocene but is always found at low altitudes (Hoffstetter and possibly older. The very early presence of a

GEODIVERSITAS • 2001 • 23 (4) 643 Saint-André P.-A. & De Iuliis G.

Megatherium species that possesses a femur with Dompierre, J. Fuoco, F. Pujos and M. Souza pro- prominent torsion on the Bolivian Altiplano vided help with logistics. This paper is a contribu- indicates that the M. altiplanicum n. sp.-M. ame- tion to the projects Universidad Nacional de La ricanum clade (subgenus Megatherium) originat- Plata N336, Agencia de Promoción Científica y ed either on the Altiplano or in a region from Tecnológica PICT 7-6348, and Fundación which remains are unknown or undescribed, and Antorchas No. A-13740/1-78. that the emergence of the genus Megatherium (including M. medinae) probably dates to near the beginning of the Pliocene. REFERENCES An evolution on the Altiplano would cast doubt AMEGHINO C. & KRAGLIEVICH L. 1921. — on some of the minor conclusions drawn by Descripción del “Megatherium gallardoi” Marshall & Sempéré (1992), such as that there is C. Ameghino descubierto en el Pampeano inferior no paleontological data that supports the hypoth- de la ciudad de Buenos Aires. Anales del Museo de esis of an endemic Altiplano-Puna fauna, and Historia Natural de Buenos Aires 31: 135-156. BOULE M. & THÉVENIN A. 1920. — Mammifères fos- that this region was not a site of significant in situ siles de Tarija. Mission scientifique G. De Créqui- evolution. These authors postulated that recur- Monfort et E. Sénéchal de la Grange. Librarie H. Le rent deposition of ash sheets during the Miocene Soudier, Paris, 255 p. CABRERA Á. 1928. — Sobre algunos megaterios plio- and Pliocene resulted in repetitive and massive cenos. Revista del Museo La Plata 31: 339-352. regional extinctions on the Altiplano-Puna, each CARTELLE C. 1992. — Edentata e megamamíferos her- followed by the reestablishment of faunae of low bívoros extintos da Toca dos Ossos (Ourolândia, diversification through immigration from sur- Bahia, Brasil). Tese de Doutorado, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil, rounding lowland areas. 301 p. However, it is possible that M. altiplanicum n. sp. CARTELLE C. & DE IULIIS G. 1995. — Eremotherium evolved in situ from a form more hypsodont laurillardi - the Panamerican Late Pleistocene than, for example, Eremotherium. Such a megatheriid sloth. Journal of Paleontology 15 (4): 830-841. postulated form, ancestral to the species of CASAMIQUELA R. M. & SEPULVEDA F. 1974. — Megatherium possessing a prominently twisted Catalogación crítica de algunos vertebrados fósiles femur, probably resembled the Pleistocene Chilenos. III: Los megaterioideos. Sobre Megathe- M. medinae, which was apparently restricted to rium medinae Philippi. Ameghiniana 11 (2): 97-123. CASINOS A. 1996. — Bipedalism and quadrupedalism high elevations in the Chilean (and possibly the in Megatherium: an attempt at biomechanical Peruvian and Ecuadorian) Andes. reconstruction. Lethaia 29: 87-96. CUVIER G. 1796. — Notice sur le squelette d’une très Acknowledgements grande espèce de quadrupède inconnue jusqu’à présent, trouvé au Paraquay, et déposé au cabinet We thank F. Anaya-Daza (MNNP BOL), d’histoire naturelle de Madrid. Magasin ency- J. Bonaparte (MACN), J. Flynn (FMNH), clopédique, ou Journal des Sciences, des Lettres et des C. McGowan and H.-D. Sues (ROM), C. de Arts (1): 303-310; (2): 227-228. DE IULIIS G. 1994. — Relationships of the Muizon (IFEA), and R. Pascual (MLP) for facili- Megatheriinae, Nothrotheriinae, and Planopsinae: tating our research within their institutions. We some skeletal characteristics and their importance appreciate the efforts of H. G. McDonald and for phylogeny. Journal of Vertebrate Paleontology 14 A. Ohler for critical review of the manuscript. (4): 577-591. DE IULIIS G. 1996. — A Systematic Review of the Their suggestions and comments helped improve Megatheriinae (Mammalia: Xenarthra: Mega- its scientific merit. We acknowledge the help of S. theriidae). Doctoral Thesis, University of Toronto, F. Vizcaíno in calculations of mass estimates, D. Toronto, Canada, 781 p. Pulerà for illustrations (Figs 1; 2; 8 and 9), and L. DE IULIIS G. & CARTELLE C. 1999 — A new giant megatheriine ground sloth (Mammalia: Xenarthra: Yick, E. Knapp, and D. Serrette and P. Loubry Megatheriidae) from the late Blancan to early (MNHN) for photographic reproductions and Irvingtonian of Florida. Zoological Journal of the arrangements. C. De Iuliis, T. De Iuliis, H. Linnean Society 127: 495-151.

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DE IULIIS G. & SAINT-ANDRÉ P.-A. 1997. — bearing Tertiary of South America. Palaeo- Eremotherium sefvei n. sp. (Mammalia: Xenarthra: vertebrata mémoire extraordinaire 1983: 1-93. Megatheriidae) from the Pleistocene of Bolivia. MARSHALL L. G. & SALINAS P. 1991. — The Lorenzo Geobios 30 (3): 453-461. Sundt collection of Pleistocene mammals from FARIÑA R. A., VIZCAÍNO S. F. & BARGO M. S. Ulloma, Bolivia in the Museo Nacional de Historia 1998. — Body size estimations in Lujanian (Late Natural, Santiago, Chile, in SUAREZ-SUROCO R. Pleistocene-Early Holocene of South America) (ed.), Fósiles y Facies de Bolivia. Volumen I: mammal megafauna. Mastozoología Neotropical Vertebrados. Revista Technica de Yacimientos 5 (2): 87-108. Petroliferos Fiscales Bolivianos 12 (3-4): 685-692. HOFFSTETTER R. 1952. — Les mammifères pléis- MARSHALL L. G. & SEMPÉRÉ T. 1991. — The Eocene tocènes de la République de l’Équateur. Mémoires to Pleistocene vertebrates of Bolivia and their strati- de la Société géologique de France nouvelle série 31 graphic context: a review, in SUAREZ-SUROCO R. (66), 391 p. (ed.), Fosiles y Facies de Bolivia. Volumen I: HOFFSTETTER R. 1986. — High Andean mammalian Vertebrados. Revista Tecnica de Yacimientos faunas during the Plio-Pleistocene, in VUILLEUMIER Petroliferos Fiscales Bolivianos 12 (3-4): 631-652. F. & MONASTERIO M. (eds), High Altitude Tropical MARSHALL L. G. & SEMPÉRÉ T. 1992. — Evolution of Biogeography. Oxford University Press; the the neotropical land mammal fauna in its American Museum of Natural History, New York: geochronologic, stratigraphic and tectonic context, 218-245. in GOLDBLATT P. (ed.), Biological Relationships HOFFSTETTER R., MARTINEZ C., MUNOS-REYES J. & between Africa and South America. Yale University TOMASI P. 1971. — Le gisement d’Ayo Ayo (Bolivie), Press, New Haven: 329-392. une succession stratigraphique Pliocène-Pléistocène MARSHALL L. G., SWISHER C. C., LAVENU A., datée par des mammifères. Comptes Rendus de HOFFSTETTER R. & CURTIS G. H. 1992. — l’Académie des Sciences 273 (D): 2472-2475. Geochronology of the mammal-bearing late INTERNATIONAL COMMISSION ON ZOOLOGICAL Cenozoic on the Northern Altiplano, Bolivia. NOMENCLATURE 1999. — International Code of Journal of South American Earth Sciences 5 (1): 1-19. Zoological Nomenclature. 4th ed. International Trust MCDONALD H. G. 1977. — Description of the for Zoological Nomenclature, London, 306 p. Osteology of the Extinct Gravigrade Edentate JANIS C. 1990. — Correlation of cranial and dental Megalonyx with Observations on its Ontogeny, variables with body size in ungulates and macropo- Phylogeny and Functional Anatomy. Master of dids, in DAMUTH J. & MACFADDEN B. J. (eds), Science Thesis, University of Florida, Gainesville, Body Size in Mammalian Paleobiology: Estimation USA, 328 p. and Biological Implications. Cambridge University OWEN R. 1856. — On the Megatherium Press, Cambridge: 225-299. (Megatherium americanum Cuvier and Blumen- KRAGLIEVICH L. 1925a. — Paramegatherium nazarrei bach). III: the Skull. Philosophical Transactions of the nuevo megateridio gigantesco descubierto en el Royal Society of London 146 (2): 571-589. Territorio del Neuquén. Anales del Museo Nacional PAULA COUTO C. DE 1979. — Tratado de de Historia Natural 33: 237-254. Paleomastozoologia. Academia Brasileira de Ciências, KRAGLIEVICH L. 1925b. — Cuatro nuevos gravígrados Rio de Janeiro, 590 p. de la fauna Araucana Chapadmalalense. Anales del PAZ F., ALVAREZ J., PONCE J., ZAPATA H., VELAZQUEZ Museo Nacional de Historia Natural de Buenos Aires M. & LLANOS R. 1966. — Carte géologique de 33: 215-235. Corque (1/100 000). Departamento Nacional de KRAGLIEVICH L. 1930. — La formación friaseana de Geología, La Paz: Feuille n° 6038. río Frías, río Fenix, Laguna Blanca, etc., y su fauna PHILIPPI R. A. 1893. — Vorläufige Nachricht über de mamíferos. Physis 10 (35): 127-161. fossile Säugethierknochen von Ulloma, Bolivia. KRAGLIEVICH L. 1931. — Megatherium lundi seijoi Zeitschrift der deutschen geologischen Gesellschaft 45: nueva subespecie pleistocena del Uruguay. Revista 87-96. de la Sociedad “Amigos de la Arqueología” 5: 81-89. ZETTI J. 1964. — El hallazgo de un Megatheriidae en MARSHALL L. G., HOFFSTETTER R. & PASCUAL R. el “médano invasor” del SW de Toay, Provincia de 1983. — Geochronology of the continental mammal- La Pampa. Ameghiniana 3 (9): 257-265.

Submitted on 24 May 2000; accepted on 19 July 2001.

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