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Anisodontherium from the Late Miocene of north-western Argentina

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Brandoni D., Powell J. E., Gonzales O. E.

Acta Palaeontologica Polonica

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2012

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tom 57

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nr 2

The fossil record of Megatheriinae (Tardigrada, Megatheriidae) in Argentina extends from the Colloncuran (Middle Miocene of Patagonia) to the Lujanian (Late Pleistocene–Early Holocene of the Pampean region). In the Late Miocene of north−western Argentina, Megatheriinae is represented by just three species belonging to a single genus, Pyramiodontherium. Here, we describe a partial mandible and the phalanges of a third digit of the manus recovered from the Saladillo Formation (Upper Miocene) of Tucumán Province, and assign them to Anisodontherium sp. Anisodontherium is primarily characterized by mesiodistally compressed molariforms, an anterior margin of the coronoid process located posterior to m4, and a posterior margin of the mandibular symphysis located anterior to m1. While these features can also be observed in A. halmyronomum from the Arroyo Chasicó Formation (Buenos Aires Province, Pampean region), Anisodontherium sp. is smaller and more slender than the former. The shape of each molariform of Anisodontherium affects the total length of the molariform tooth row, and thus the interpretation of some characters used in cladistic and paleobiological analyses. The material described here adds to the knowledge of the mandibular and dental anatomy of early megatheriines. In addition, the occurrence of Anisodotherium in Tucumán Province provides the first record of this genus outside the Pampean region, and increases the diversity of megatheriines during the Late Miocene–Pliocene of north−western Argentina.

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Ulnar dimensions and fossoriality in armadillos

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Vizcaino S. F., Farina R. A., Mazzetta G. V.

Acta Theriologica

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1999

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tom 44

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nr 3

Ulnar dimensions were measured in 14 species of armadillos (Xenarthra: Dasy- podidae). An index of f'ossorial ability (IFA) was constructed, relating the length of the olecranon process to the remaining length of the ulna. For comparative purposes, the same measurements were taken in 14 other species of mostly South American mammals belonging to 3 orders and 11 families. The fossorial habits of these mammals were classified into 3 categories: (1) species mostly cursorial and non-digging; (2) species that often dig, but to which digging plays no essentia! part in their alimentary strategy and are not burrowers; and (3) species that are burrowers. IFA means of the studied mammal orders were compared using one-way analysis of variance on log-trans formed data. Bivariate size allametry between ulnar dimensions and body mass was assessed by fitting (least squares and geometric mean) linear regressions of log-transformed data. It is concluded that the IFA discriminates among the species according to their fossorial habits within orders, but it is not equally useful in distinguishing fossorial species between orders. In armadillos, the relationships between ulnar dimensions and body mass are isometrical, Finally, the IFA is independent of body size.

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Hypsodonty in Pleistocene ground sloths

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Bargo M. S., De Iuliis G., Vizcaino S. F.

Acta Palaeontologica Polonica

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2006

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tom 51

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nr 1

Although living sloths (Xenarthra, Tardigrada) are represented by only two genera, their fossil relatives form a large and diverse group. The evolution of hypsodonty, the crown height of a tooth, has traditionally been viewed as a response to dietary shifts toward abrasive vegetation. But recent work indicates that hypsodonty is also due to the higher prevalence of grit and dust in more open environments. The teeth of sloths are both high−crowned and open−rooted, or hypselodont, but distinctions between the selective factors acting to produce differing degrees of hypsodonty have not been rigorously considered. A comparative analysis of hypsodonty was performed in eleven species of Pleistocene sloths. It suggests that differences in hypsodonty may be explained by dietary preferences, habitat and habits. Among mylodontids, morphologic and biomechanical analyses indicate that hypsodonty was unlikely to be due solely to feeding behavior, such as grazing. Some mylodontids (e.g., Scelidotherium leptocephalum, Lestodon armatus, Glossotherium robustum, Mylodon darwini) were capable diggers that likely dug for food, and ingestion of abrasive soil particles probably played a considerable role in shaping their dental characteristics. Increased hypsodonty over time in Paramylodon harlani, however, is apparently due to a change in habitat from closed to more open environments. Geographical distributions of the megatheriids Eremotherium and Megatherium indicate differing habitats as possible factors in hypsodonty differences. In summary, among Tardigrada hypsodonty is apparently affected by diet, habitat and habit. The absence of enamel must be responsible for much of the hypsodonty observed in xenarthrans, which obscures the interpretation of contribution of each of the mentioned factors.

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Distribution and use of burrows and tunnels of Chaetophractus villosus [Mammalia, Xenarthra] in the Eastern Argentinean pampas

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Abba A. M., Udrizar Sauthier D. E., Vizcaino S. F.

Acta Theriologica

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2005

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tom 50

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nr 1

Burrows and tunnels built byChaetophractus villosus (Desmarest, 1804) (hairy armadillo) were studied in a farming area located in the Argentinean pampas, Buenos Aires Province, Argentina. Fifty-six structures were selected and carefully excavated for this study. Data on diameter, form, and orientation of the entrance, angle, length, and depth of the galleries, and spatial distribution of the structures were recorded. The structures were separated into two types: simple and complex, both located in high terrain. Simple structures are shorter than complex ones and are built when animals are in search of food or as temporary shelters. Complex structures are built as home burrows. The orientation of the entrances of both kinds of burrows is related to the prevalent wind direction.

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Ecological differences between two sympatric species of armadillos [Xenarthra, Mammalia] in a temperate region of Argentina

80%

Abba A. M., Cassini M. H.

Acta Theriologica

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2010

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tom 55

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nr 1

35-44

Morpho-physiological specialization related to foraging can act as constraints on behaviour and ecological patterns of abundance and distribution. We tested this prediction in two species (weeping or screaming hairy armadillos Chaetophractus vellerosus Gray, 1865 and mulitas Dasypus hybridus Desmarest, 1804) that represent the two subfamilies of armadillos (Dasypodidae, Xenarthra): Euphractinae and Dasypodinae. The first subfamily possesses a well-developed masticatory apparatus that is considered primitive within the Xenarthra, while Dasypodinae show reductions in various aspects of cranial morphology. We sampled signs (burrows and foraging holes) and captured both species on 34 farms randomly selected in the north-eastern Pampas region of Argentina. We analyzed several niche dimensions. The two species showed significant differences in habitat use, seasonal patterns and diet. Weeping armadillos were generalists in their diet and active throughout the year. They were associated with calcareous-sand soil, as expected for a burrowing animal of the deserts. They tolerated a wide range of environmental conditions. We found that mulitas are myrmecophagous, and that they demonstrated a reduction in body temperature and activity during the cold season. As expected from their geographical distribution, mulitas used mainly vegetation with high cover and were associated with humic soils. Niche segregation between the two species of armadillos appeared to originate from different degrees of dietary specialization.

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The ground sloth Megatherium americanum: skull shape, bite forces, and diet

70%

Bargo M. S.

Acta Palaeontologica Polonica

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2001

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tom 46

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nr 2

Megatherium americanum (late Pleistocene of South America) has traditionally been regarded a herbivore, but its dietary habits have not been considered in terms of a morphofunctional analysis. This study describes and analyses the morphology of the masticatory apparatus in order to interpret the jaw mechanics of M. americanum, and thus to infer its diet and behaviour. The results are compared with those for the mylodontid Glossotherium robustum and the extant sloth Bradypus variegatus. The areas of origin and insertion of the masticatory musculature were reconstructed, and the moment arms generated by this musculature were estimated so that the mechanics of the feeding apparatus might be described. These analyses indicate that M. americanum was well adapted for strong and mainly vertical biting. The teeth are extremely hypsodont and bilophodont, and the sagittal section of each loph is triangular with a sharp edge. This suggests that the teeth were used mainly for cutting, rather than grinding, and that hard and fibrous food was not the main dietary component. The diet of M. americanum merits more rigorous analysis, but the evidence provided here indicates that it probably had a browsing diet in open habitats, but also could have fed on moderate to soft tough food.

Ograniczanie wyników

3 Acta Palaeontologica Polonica

3 Acta Theriologica

3 Vizcaino S. F.

2 Abba A. M.

2 Bargo M. S.

1 Brandoni D.

1 Cassini M. H.

1 De Iuliis G.

1 Farina R. A.

1 Gonzales O. E.

1 Mazzetta G. V.

1 Powell J. E.

1 Udrizar Sauthier D. E.

1 2012

1 2010

1 2006

1 2005

1 2001

1 1999

Anisodontherium from the Late Miocene of north-western Argentina

Ulnar dimensions and fossoriality in armadillos

Hypsodonty in Pleistocene ground sloths

Distribution and use of burrows and tunnels of Chaetophractus villosus [Mammalia, Xenarthra] in the Eastern Argentinean pampas

Ecological differences between two sympatric species of armadillos [Xenarthra, Mammalia] in a temperate region of Argentina

The ground sloth Megatherium americanum: skull shape, bite forces, and diet