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We present a revision, dating and interpretation of the Late Pleistocene megafauna of Guatemala based on paleontological material located in collections in the country and other fossils housed in the American Museum of Natural History, New York. Assemblages are dominated by proboscideans (Cuvieronius) and xenarthrans (Eremotherium, Glyptotherium), while co-occurring Equus and Mixotoxodon are significantly less frequent, and Holmesina, Palaeolama, Tapirus, Neocherus, Mammuthus and other ground sloth taxa (Paramylodon; Megalonyx) are rare. Contrary to published records the faunal assemblage is dominated by North American faunal elements. The underrepresentation of typical South American fauna therefore suggests a more southernly located biogeographic juncture between the two subcontinents, at least for the Late Pleistocene. The biogeographical barrier was either formed by the high mountain chains, or alternating periods of low and high precipitation that triggered the intermittent expansion of either grass- or woodland, thus leading to an alternating filter for either grazers or browsers. The presence of an oak-dominated forest vegetation with Mixotoxodon, Eremotherium and Cuvieronius supports high precipitation rates during MIS 3 and 2, followed by drought during the Late Pleistocene deglaciation. The expansion of grassland during the Younger Dryas period favored the migration of Mammuthus along the Mesoamerican Corridor, which is otherwise absent in Guatemala. Our data also suggest a survival of Cuvieronius into the early Holocene in the southeastern lowlands of Guatemala along the Motagua river. Our review is important as Guatemala is key to understanding migrations along the Mesoamerican Corridor that acted as a bridge but also as a filter of faunal interchange between North- and South America.

New mylodontine (Xenarthra, Pilosa) sloth remains from the late Pleistocene tar seep localities of Corralito (Ecuador) and Talara (Peru) are described, and the taxonomic history of the extinct ground sloth genus Glossotherium is reviewed. Based on the new material and comparisons with Glossotherium robustum, Glossotherium wegneri, and the North American taxon, Paramylodon harlani, the species Glossotherium tropicorum is considered to be valid and a new definition of its diagnostic characters is provided. Glossotherium tropicorum is similar in size to Glossotherium robustum and Glossotherium wegneri but differs in several respects from these species, such as having a more elongated and slender skull. In this respect it more closely resembles Paramylodon harlani in North America, which is also similar in size. Glossotherium tropicorum is one of two mylodontine sloths found in the upper Pleistocene of north-western South America, the other being Glossotherium wegneri. While both are present in this region their individual distributions did not overlap and the two species have not been recovered together in a fauna. The distribution of Glossotherium tropicorum is restricted to lowland coastal areas whereas Glossotherium wegneri is found inland and in the highland areas of the Andes, suggesting significant differences in their ecology. Fil: De Iuliis, Gerardo. University of Toronto; Canadá. Royal Ontario Museum; Canadá Fil: Cartelle, Cástor. PUC Minas; Brasil Fil: McDonald, H. Gregory. Utah State Office; Eslovaquia Fil: Pujos, François Roger Francis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

Paramylodon harlani was a large ground sloth recorded across North America, from Canada to Mexico. In Mexico, it is known from several late Pleistocene localities, but most of these records just mention the taxon in passing and few specimens have been described or illustrated. In this work, we describe a left tibia from the Valsequillo Basin, Puebla state. Its morphology and measurements allowed us to identify it as Paramylodon harlani, adding a new record for Mexico. In Mexico, P. harlani occurred mainly in the Trans-Mexican Volcanic Belt, central Mexico, with some records in the north and southeastern part of the country. Most localities are located between 1500 to 2000 m.a.s.l. Paleoenvironmental and paleoclimatic inference in some localities of Mexico where P. harlani occurred, showed heterogenous vegetation dominated by grasslands, and agree with the preferred habitat proposed for this species based on localities in the United States. This indicates that P. harlani could inhabit different environments, from grasslands to more wooded areas, and this adaptation allowed it to extend its range from the north to the southeast of Mexico.

Associated osteoderms of unique aspect have been found in Ensenadan age deposits near San Pedro, in the Pampean Region of Argentina. Their general shape closely resembles that of mylodontid sloths. They are unique in presenting a homogeneous octahedral shape, contrasting with the heterogeneous shape of other ground sloth osteoderms. The lack of expanded spaces within the bone is shared with some other mylodontid sloths. Histologically, the bone is well vascularized, full of fiber bundles (including Sharpey's fibers), and very similar to the condition in Mylodon darwinii. The lack of individualized fibers near and perpendicular to the external surface suggests a relatively deeper position in the dermis than in the Pleistocene ‘Paramylodon’ garbanii. The taxon to which these novel osteoderms belonged is uncertain, but the possible carriers are discussed.

The Fairmead Landfill locality contains a diverse middle Irvingtonian, (0.78–0.55 Ma), vertebrate fauna that includes three sloths, Megalonyx wheatleyi, Nothrotheriops shastensis and Paramylodon harlani. The co-occurrence of these three genera in a single fauna is relatively rare in both the Irvingtonian and Rancholabrean and this is only the fourth documented Irvingtonian fauna to contain all three sloth genera. The presence of the three different sloths, each of which had different ecological requirements, indicates the presence of a variety of different habitats at this time and a heterogeneous landscape. Preliminary analysis of pollen from the site supports the interpretation of the existence of a mosaic of plant communities, but a landscape dominated by a mesic grassland. This interpretation is also supported by the total faunal diversity that includes taxa associated with woodlands as well as open habitat and taphonomic differences in the preservation and relative abundance of the different sloths. Evolutionarily the Fairmead Landfill sloths show a suite of morphological, size and proportional characters that indicate they represent transitional populations between older and younger members of their respective lineages.

Here we report on late Pleistocene fossil vertebrates from new and previously described localities in Santa Clara County, California. The three new localities and specimens include: a partial mammoth pelvis from UCMP V91128 (Lawrence Expressway E); a juvenile cranial specimen of Mammuthus columbi from UCMP V99597 (SCVWD “Lupe” Mammoth), now on display at the San Jose Children’s Discovery Center; and a relatively diverse assemblage of medium- to large-sized mammals, including a nearly complete forelimb of Paramylodon harlani from UCMP V99891 (Babcock’s Bones). We also reassess specimens and assemblages from the following eight previously known localities: Molecular Medicine Building (UCMP V90003); Alma Street Underpass at Page Mill Road (USGS M1203); Mountain View Dump (USGS M1227); Sunnyvale Sewer (USGS M1218); Calabaza, Sunnyvale Sewer (USGS M1218A); Matadero Creek (USGS M1001); Matadero Creek, Veteran’s Hospital (USGS M1202); and Milpitas (UCMP V4916). All localities discussed, except Matadero Creek and Veterans Hospital, are mapped in areas with surficial Holocene deposits, and therefore, these Pleistocene-aged assemblages suggest that Pleistocene deposits are closer to the surface in Santa Clara County than may have been previously thought. Material described here highlights the needed resources for mitigation management in Santa Clara County.

New ground sloths (Mammalia, Xenarthra, Mylodontidae) from the Neogene of the Bolivian Altiplano. Two new Mylodontinae (Xenarthra, Tardigrada, Mylodontoidea) from the Bolivian Altiplano are described. One of them, Pleurolestodon dalenzae n. sp., was discovered a few meters below a volcanic tuff, Toba 76, that may be used as a reference stratigraphic level and is dated at 5.4 Ma; it could be Huayquerian (late Miocene) or at the Huayquerian-Montehermosan boundary in age. The other taxon, Simomylodon uccasamamensis n. gen., n. sp., was recovered from many localities of a horizon bounded below by Toba 76 and above by another volcanic level, the 2.8 Ma Ayo Ayo tuff; its age is Montehermosan-Chapadmalalan (early and middle Pliocene). Analysis of these taxa indicates that they are Mylodontidae more closely related to Glossotherium, Glossotheridium, Kiyumylodon and Paramylodon than to Lestodon or Thinobadistes.

Nomenclatural confusion has existed within the Mylodontinae for several genera, and has resulted in the supposition that Paramylodon of North America is synonymous with Glossotherium of South America. A taxonomic revision of crania for Glossotherium and Paramylodon upholds their separation as distinct genera and provides a list of diagnostic characters that have been lacking. Assessment was made using principal components analysis for suites of cranial and mandibular measurements, evaluation of ratios and measurement distribution, and by examining qualitative characters. Results show the greatest characterization for the skull comes from differences relating to cranial length versus width, whereas the mandible is predominantly distinguished by qualitative characters of the predental spout. Examination of the Pliocene species Glossotherium chapadmalense from South America shows a combination of characters indicative of each genus, but exhibits more with Glossotherium and is tentatively retained under that genus. The mix of characters indicates that G. chapadmalense is the likely ancestor to Paramylodon, although when and where the transition took place is still unclear. During the evolutionary transition, Paramylodon crania emphasized an increase in length of the palate, whereas those of Glossotherium emphasized an increase in cranial width. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155, 885–903.

Throughout the Cenozoic, the North American mammalian fauna has been enriched by the appearance of new taxa originating on different continents. During most of the Tertiary, the primary source area of these new taxa was Eurasia with dispersal across some version of the Bering Land Bridge. In the late Pliocene (Blancan) ca. 2.5 mya, the creation of the Panamanian Land Bridge permitted the northward dispersal of species of South American origin including ground sloths. One of these sloths was “Glossotherium” chapadmalense, which in turn gave rise to the Pleistocene species Paramylodon harlani. Mammoths first appear in North America at the beginning of the Irvingtonian ca. 1.9 mya. Despite originating on two different continents, the two species are often found together in North American Pleistocene faunas and shared a common habitat. Both of these lineages are commonly interpreted as grazers, indicative of open grassland habitat, and both of these exotic species shared this habitat with North American endemic species such as horses, also interpreted as grazers. Despite their association in North American faunas, mammoths did not disperse into South America and mylodont sloths were unable to disperse into Eurasia. This suggests there were some aspects of their ecology they did not have in common and there existed a limited zone of conditions that permitted them to share common habitat. There is no evidence that the appearance of either species in North America resulted in the extinction of any native species. The question is how these different species, immigrants and endemics, were able to avoid competition, coexist, and become integrated into a single fauna, thus enriching the overall North American Pleistocene fauna.

The late Pleistocene ground sloth Paramylodon harlani was widely distributed across North America, but it is represented in Arizona by only 2 records. These include a nearly complete skeleton from the Richville Gravels near Springerville, Apache County, and a second partial skeleton from Shonto, Navajo County. Both specimens are from reportedly lacustrine deposits and suggest that the species was not adapted to xeric conditions. Thus, its distribution in the Southwest and potential for dispersal might have been determined by the presence of permanent water sources.

The hyoid apparatus in fossil Xenarthrans is rarely preserved. Its largest bone, the stylohyal, is the most frequently found as an isolated element. It is known for some species of Pleistocene ground sloths (Megalonyx jeffersonii, Megatherium americanum, Paramylodon harlani, Nothrotheriops shastensis, Glossotherium robustum and Scelidotherium leptocephalum) but not for the largest mylodontid Lestodon armatus. Here we describe a right stylohyal found in the late Pleistocene megafaunal bonebed of the Arroyo del Vizcaino site, Uruguay, as two perfectly matched pieces that were within a few centimeters of each other. A small notch, possibly a conchoidal flaked perimortem fracture, is observed in the lateral face. The specimen, whose general form is a sinusoid cylinder with the proximal end expanded and compressed, must have belonged to a juvenile individual, since it lacks both the distal and proximal surfaces that articulate with the skull and the epihyal, respectively. Instead, both ends show an irregular surface as those seen in the contact with the growth cartilage. Additionally, its maximum length is 105 mm, larger than the equivalent part of the stylohyal of adult Glossotherium. At the expanded proximal end that articulates with the skull the large fossa found in Glossotherium and Scelidotherium cannot be observed, which could be due to a taxonomic difference, to the stage of growth or both of them. The bone shows marks, several interpreted as caused by trampling and at least one with features as those left by human tools. P. Sebastian Tambusso. Seccion Paleontologia, Facultad de Ciencias, Universidad de la Republica, Igua 4225, 11400 Montevideo, Uruguay pasebita@gmail.com H. Gregory McDonald. Museum Management Program, National Park Service, 1201 Oakridge Drive, Fort Collins, Colorado 80521 USA greg_mcdonald@nps.gov Richard A. Farina. Seccion Paleontologia, Facultad de Ciencias, Universidad de la Republica, Igua 4225, 11400 Montevideo, Uruguay dogor@netgate.com.uy

Documentamos aquí por primera vez los mamíferos del Pleistoceno tardío de la localidad de El Hatillo en la península de Azuero en Panamá, originalmente reportado por C. L. Gazin en 1957. Los siguientes taxa están presente: Hoplophorinae?, Glyptotherium floridanum, Eremotherium laurillardi, Paramylodon harlani, Equus conversidens, Platygonus sp., Odocoileus sp., Mixotoxodon larensis y Cuvieronius hyodon. Este es un conjunto característico de mamíferos del Pleistoceno Tardío de Centroamérica destacado por fósiles de Eremotherium en asociación con fósiles de Mixotoxodon y Equus. Me refiero a este tipo de asociación como montaje EME y postulo que la mayoría de estos montajes de Centroamérica son de edad del Pleistoceno Tardío. Los montajes EME representan una fauna mixta de pasteadores y ramoneadores que eran muy común en toda Centroamérica durante uno o más de los fines interestadiales del Pleistoceno. Late Pleistocene mammals from the El Hatillo locality on the Azuero Peninsula in Panama, originally reported by C. L. Gazin in 1957, are documented here for the first time. The following taxa are present: Hoplophorinae?, Glyptotherium floridanum, Eremotherium laurillardi, Paramylodon harlani, Equus conversidens, Platygonus sp., Odocoileus sp., Mixotoxodon larensis and Cuvieronius hyodon. This is a characteristic assemblage of late Pleistocene mammals from Central America that is dominated by fossils of Eremotherium in association with fossils of Mixotoxodon and Equus. I refer to such associations as EME assemblages and posit that most of these assemblages from Central America are of Late Pleistocene age. EME assemblages represent a mixed fauna of grazers and browsers that was common across Central America during one or more of the Late Pleistocene interstadials.