Caviomorph rodents (Rodentia: Caviomorpha) are an anatomically variable group with diverse ecological and morphological types, including cursorial, digging, fossorial and swimming forms. Their appendicular skeleton is rather generalized and extreme modifications or reductions in the long bones of limbs are not present. It is of special interest to evaluate functional adaptive variations of the appendicular skeleton within this group. Although much work has been devoted to study structure, function, and kinematics of legs in mammals, most studies do not consider particular functions and behaviour within different mammalian lineages. Morphometric and biomechanical studies were performed to test the relationship between adaptation and morphology of the bones of the proximal and middle limb segments in terrestrial caviomorph rodents. Fifty-four specimens belonging to 10 species with different limb adaptations and representing a wide range of body sizes were measured. Diameters and functional lengths of long bones were taken and nine functional indices were built. Humerus (HRI) and ulna (URI) robustness, humerus deltoid (SMI) and epicondyle (EI) development, olecranon proportion (IFA), femur (FRI) and tibia (TRI) robustness, and gluteal muscle insertion at femur (GI), were calculated. Only TRI and, to a lesser degree, SMI and EI, were significantly related to body mass. A functional sequence (cursorial-generalized-occasional diggingdiggers) which seems to reflect an increase in force and muscular development in middle segments of the fore limb is recognized. The hind limb shows a decrease in the speed efficiency of the femur and an increase in limb robustness in the transition from cursorial to digging forms. Although overlapping of speed and force functions in the limbs is evident, functional differentiation for speed in the proximal, and force in the middle segments can be inferred.

The early Miocene Santa Cruz Formation (SCF) in southern Patagonia hosts the Santacrucian South American Land Mammal Age (SALMA), whose age is known mainly from exposures along the Atlantic coast. Zircon U-Pb ages were obtained from intercalated tuffs from four inland sections of the SCF: 17.36 ±0.63 Ma for the westernmost Río Bote locality, and 17.04± 0.55 Ma to 16.32± 0.62 Ma for central Río Santa Cruz localities. All ages agree with the bounding age of underlying marine units and with equivalent strata in coastal exposures. New ages and available sedimentation rates imply time spans for each section of ~18.2 to 17.36 Ma for Río Bote and 17.45 to 15.63 Ma for central Río Santa Cruz (Burdigalian). These estimates support the view that deposition of the SCF began at western localities ~1 Ma earlier than at eastern localities, and that the central Río Santa Cruz localities expose the youngest SCF in

Among the fossils of hitherto unknown mammals that Darwin collected in South America between 1832 and 1833 during the Beagle expedition were examples of the large, heavily armored herbivores later known as glyptodonts. Ever since, glyptodonts have fascinated evolutionary biologists because of their remarkable skeletal adaptations and seemingly isolated phylogenetic position even within their natural group, the cingulate xenarthrans (armadillos and their allies). In possessing a carapace comprised of fused osteoderms, the glyptodonts were clearly related to other cingulates, but their precise phylogenetic position as suggested by morphology remains unresolved. To provide a molecular perspective on this issue, we designed sequence-capture baits using in silico reconstructed ancestral sequences and successfully assembled the complete mitochondrial genome of Doedicurus sp., one of the largest glyptodonts. Our phylogenetic reconstructions establish that glyptodonts are in fact deeply nested within the armadillo crown-group, representing a distinct subfamily (Glyptodontinae) within family Chlamyphoridae. Molecular dating suggests that glyptodonts diverged no earlier than around 35 million years ago, in good agreement with their fossil record. Our results highlight the derived nature of the glyptodont morphotype, one aspect of which is a spectacular increase in body size until their extinction at the end of the last ice age.

Armadillos are a very diverse group ranging from non-fossorial Tolypeutini through to the powerful diggers like the giant armadillo Priodontes maximus to the totally subterranean Chlamyphorini. A previous study demonstrated a close relationship between the relative length of the olecranon of the ulna (index of fossorial ability, IFA) and the fossorial ability of armadillos. This study examines a wide range of limb proportions to explore the biomechanical correlates with fossorial ability. The study demonstrates that the indices of the forelimb (brachial index, shoulder moment index and IFA) do correlate well with digging habits, but also reveals some interesting exceptions, particularly in the most fossorial and most cursorial forms. On the other hand, the hindlimb indices apparently do not correlate with digging habits, but seem to be in¯uenced more by body size. The correlations among the forelimb indices are quite strong and positive but correlations between forelimb and hindlimb indices are negative or very low. It is apparent that there is still much to be learned about structure and function in armadillos.

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R. A. and Mazzetta G. V. 1999. Ulnar dimensions and fossoriality in armadillos. Acta Theriologica 44: 309-320.Ulnar dimensions were measured in 14 species of armadillos (Xenarthra: Dasypodidae). An index of fossorial 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 essential 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-transformed data. Bivariate size allometry 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.CONICET,

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Early Miocene sloths are represented by a diversity of forms ranging from 38 to 95 kg, being registered mainly from Santacrucian Age deposits in southern-most shores of Patagonia, Argentina. Their postcranial skeleton differs markedly in shape from those of their closest living relatives (arboreal forms of less than 10 kg), Bradypus and Choloepus. In order to gain insight on functional properties of the Santacrucian sloths forelimb, musculature was reconstructed and a comparative, qualitative morphofunctional analysis was performed, allowing proposing hypotheses about biological role of the limb in substrate preferences, and locomotor strategies. The anatomy of the forelimb of Santacrucian sloths resembles more closely extant anteaters such as Tamandua and Myrmecophaga, due to the robustness of the elements, development of features related to attachment of ligaments and muscles, and conservative, pentadactylous, and strong-clawed manus. The reconstructed forelimb musculature was very well developed and resembles that of extant Pilosa (especially anteaters), although retaining the basic muscular configuration of generalized mammals. This musculature allowed application of powerful forces, especially in adduction of the forelimb, flexion and extension of the antebrachium, and manual prehension. These functional properties are congruent with both climbing and digging activities, and provide support for proposed Santacrucian sloths as good climbing mammals, possibly arboreal or semiarboreal, being also capable diggers. Their climbing strategies were limited, thus these forms relied mainly on great muscular strength and curved claws of the manus to move cautiously on branches. Anat Rec, 296:305-325,