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This article analyzes the adaptations of the hindlimb of two Early Paleocene marsupials, Mayulestes ferox and Pucadelphys andinus. This analysis is based on detailed comparisons with various extant marsupials, both South American and Australian. In the case of the South American opossums, original myological data were collected and osteological-myological associations were related to their locomotor behavior. The use of Australian genera helped to improve the appraisal of the locomotory habits of the fossil taxa. Several features are indicative of the ability of Mayulestes to climb or walk on uneven surfaces (e.g., very mobile hip joint, astragalocalcaneal joint pattern), and some other features emphasize a relative agility (e.g., strongly everted iliac blades, morphology of the distal epiphysis of the femur, medially stabilized cruroastragalar joint). Pucadelphys exhibits a hindlimb relatively similar morphologically to that of Mayulestes, but with features indicating slightly increased agility and a terrestrial component that is more emphasized than in Mayulestes. The Tiupampa fossils were therefore more agile than most living didelphids and resembled the condition observed in living dasyurids more. These conclusions complement a previous study performed on the forelimb of these fossils.

In this study, the axial skeletons of two Early Paleocene marsupials, Mayulestes ferox and Pucadelphys andinus, were analyzed functionally and compared to that of six South American and three Australian species of extant marsupials. In the case of the South American opossums, myological data of the epaxial musculature were collected and analyzed and osteological-myological associations were related to locomotor behavior. Various features of the vertebral column that relate to diet or to locomotor or postural patterns were pointed out. These features include: the craniocaudal development of the neural process of the axis; the position of the anticlinal vertebra; the morphology of the neural processes of the thoracolumbar vertebrae (orientation, length, and craniocaudal width); the length, orientation, and curvature of the transverse processes of the lumbar vertebrae; and the length and robustness of the caudal vertebrae. In both fossil forms the vertebral column is mobile and allows a great range of flexion and extension of the spine, more so than in most of the living didelphids. It is emphasized here that the analysis of the axial skeleton complements and improves the conclusions provided by the forelimb and hindlimb analyses. It is proposed that Mayulestes and Pucadelphys represent an ancestral morphotype suggesting that the generalized type of locomotion of Paleocene marsupials was partly terrestrial with some climbing ability.

Alcidedorbignya inopinata Muizon & Marshall, 1987 is a basal pantodont (Placentalia, Mammalia) of small body size, from the early Palaeocene of the Santa Lucia Formation at Tiupampa, Bolivia. Tiupampa is the type locality for the Tiupampan, a South American Land Mammal age (SALMA), which is assigned an age equivalent to the basal Torrejonian 1 of North America (c. 65 Ma). Alcidedorbignya is known by exceptionally preserved specimens, which are described here. The two major specimens are an almost complete skeleton (MHNC 8372) and a partial skull (MHNC 8399), the former representing one of the best-preserved fossil placentals from the early Palaeocene and probably the oldest placental skeleton that is so completely known. These specimens are also the first eutherian skulls and skeleton ever discovered at Tiupampa, a locality which has yielded numerous metatherian skulls and partial skeletons. The remarkable preservation of the two skulls allows a detailed description of the cranial anatomy with well-identified sutures and foramina, including those of the auditory region. Through CT scanning of the skulls, the arterial and venous circulation pattern in the basicranium as well as the bony labyrinth of the inner ear were tentatively reconstructed. A thorough description of the postcranial skeleton of MHNC 8372 is also provided. Among pantodonts, Alcidedorbignya presents the closest morphological similarities with Pantolambda, the oldest and earliest diverging North American pantodont (known by skulls and skeletons), from the late early Palaeocene (Torrejonian 2 and 3) of New Mexico. Alcidedorbignya is one-third the size, much more gracile, and clearly exhibits more plesiomorphic features than Pantolambda. It is also at least 3 Ma older. Interesting similarities are also observed between the skull of Alcidedorbignya and several "condylarths", such as Maiorana, Baioconodon, Arctocyon, and Arctocyonides. The basicranium of Alcidedorbignya is also similar to that of some extant afrotheres (e.g., Tenrec) or Lipotyphla (e.g., 398GEODIVERSITAS • 2015 • 37 (4) Muizon C. de et al. Solenodon), but most of these similarities may represent placental symplesiomorphies. In fact, the cranial anatomy of Alcidedorbignya, beyond the simple thorough description of a basal pantodont, sheds light on the cranial anatomy of placentals from the earliest Paleocene, previously unknown in this detail. The postcranial skeleton of MHNC 8372 together with some isolated specimens referred to A. inopinata, is compared to adequate morphofunctional models (e.g., Solenodon, Dendrohyrax, Sciurus), which indicates that it was a moderately agile, plantigrade, generalized terrestrial mammal with good climbing ability (scansorial) and occasionally capable of standing in a bipedal position. The scutiform ungual phalanges were probably bearing nail-like hooves (or primate-like nails) and because of the absence of claws, fossorial habits are unlikely.A parsimony analysis of a data matrix including 72 taxa and 426 characters (cranial and postcranial...

Thalassocnus is a genus of "ground sloths" known from Neogene deposits, for the great majority of specimens, of the Pisco Formation (Peru). Five species are recognized, their description being currently restricted, for the most part, to the skull, mandible, and dentition. The bones of the forelimb are here described, and compared among the species of Thalassocnus and to other pilosans. The main characteristics of the forelimb of Thalassocnus relative to other sloths are the shortness of the humerus and radius, and the specialized digits. Moreover, the late species of the genus are characterized by the development of the pronator ridge of the radius, stoutness of the ulna, widening of the proximal carpal row, and shortening of the metacarpals. Analogies with extant tetrapods are proposed in order to infer plausible aquatic functions of the forelimb of Thalassocnus. In addition to paddling, it is argued that the forelimb of Thalassocnus was involved in bottom-walking, a function similarly found in extant sirenians.However, the function of the forelimb of Thalassocnus differs drastically from that of the latter, since it was likely involved in an activity related to obtaining food such as uprooting seagrass rhizomes.

ABSTRACT. Two Santacrucian borhyaenoids, Borhyaena tuberata and Prothylacinus patagonicus, are analyzed from a functional-adaptive perspective. Seven extant placental and marsupial models are examined in order to interpret the locomotor adaptations of the two fossils. These carnivorous models are characterized by various hunting types and locomotor habits, and the association of their skeletal adaptive features with diet, substrate preference, and locomotor performance permits a functional interpretation of the postcranium of Borhyaena and Prothylacinus. The analysis shows that the forelimb of Prothylacinus is modi®ed to provide strength and¯exibility for controlled climbing. This taxon exhibits semiplantigrade fore-and hind feet. Its vertebral column was¯exible, and the hindlimb suggests an active predatory mode of hunting. The tail was muscular, heavy, and was probably used as a balancing organ. By comparison, the forelimb of Borhyaena indicates a more terrestrial mode of life, with a digitigrade forefoot, and more parasagittal movements. The tail was lighter and less muscular than in Prothylacinus. Both fossils are characterized by a powerful neck musculature related to predatory habits.KEY WORDS: functional analysis, Metatheria, Miocene, South America.T H I S paper presents a functional analysis of the postcranial skeleton of Borhyaena tuberata and Prothylacinus patagonicus (Santa Cruz Formation, Patagonia) in order to reconstruct the potential locomotor activities of these two fossil mammals. Borhyaena and Prothylacinus both belong to the borhyaenoid superfamily (Marshall 1978(Marshall , 1979. The borhyaenoids were highly carnivorous South American marsupials, known from deposits that range in age from early Palaeocene to late Pliocene. The oldest specimen known, and one of the best preserved borhyaenoids, is Mayulestes ferox from the early Palaeocene of Tiupampa (Santa Lucõ Âa Formation, Bolivia). The detailed analysis of the postcranial skeleton of Mayulestes (Muizon 1998;Argot 2001Argot , 2002 highlighted primitive adaptations within the superfamily and permits a better understanding of the locomotor behaviour of younger taxa.The postcranial remains of ®ve different borhyaenoid taxa have been obtained from the Santa Cruz beds of Patagonia: Borhyaena tuberata, Cladosictis patagonica, Prothylacinus patagonicus, Pseudonotictis pusillus, and Sipalocyon gracilis (Marshall 1978(Marshall , 1979(Marshall , 1981. More than 40 myr separate Mayulestes ferox from these species. Therefore, analysis of the locomotor diversi®cation of contemporaneous taxa, in comparison with their ancestor, is of particular interest. Borhyaena and Prothylacinus are in the same size range and represent the two largest taxa of the Miocene series. They are therefore described and analyzed together. Cladosictis, Pseudonotictis, and Sipalocyon belong to a smaller size range, and are described and discussed elsewhere (Argot in press).Dealing with two predators of the same size that coexisted in the same environment raised questions as to ...

The ability to grasp and manipulate is often considered a hallmark of hominins and associated with the evolution of their bipedal locomotion and tool use. Yet, many other mammals use their forelimbs to grasp and manipulate objects. Previous investigations have suggested that grasping may be derived from digging behaviour, arboreal locomotion or hunting behaviour. Here, we test the arboreal origin of grasping and investigate whether an arboreal lifestyle could confer a greater grasping ability in musteloid carnivorans. Moreover, we investigate the morphological adaptations related to grasping and the differences between arboreal species with different grasping abilities. We predict that if grasping is derived from an arboreal lifestyle, then the anatomical specializations of the forelimb for arboreality must be similar to those involved in grasping. We further predict that arboreal species with a well-developed manipulation ability will have articulations that facilitate radio-ulnar rotation. We use ancestral character state reconstructions of lifestyle and grasping ability to understand the evolution of both traits. Finally, we use a surface sliding semi-landmark approach capable of quantifying the articulations in their full complexity. Our results largely confirm our predictions, demonstrating that musteloids with greater grasping skills differ markedly from others in the shape of their forelimb bones. These analyses further suggest that the evolution of an arboreal lifestyle likely preceded the development of enhanced grasping ability.

A major gap in our knowledge of the evolution of marsupial mammals concerns the Paleogene of the northern continents, a critical time and place to link the early history of metatherians in Asia and North America with the more recent diversification in South America and Australia. We studied new exceptionally well-preserved partial skeletons of the Early Oligocene fossil Herpetotherium from the White River Formation in Wyoming, which allowed us to test the relationships of this taxon and examine its adaptations. Herpetotheriidae, with a fossil record extending from the Cretaceous to the Miocene, has traditionally been allied with opossums (Didelphidae) based on fragmentary material, mainly dentitions. Analysis of the new material reveals that several aspects of the cranial and postcranial anatomy, some of which suggests a terrestrial lifestyle, distinguish Herpetotherium from opossums. We found that Herpetotherium is the sister group to the crown group Marsupialia and is not a stem didelphid. Combination of the new palaeontological data with molecular divergence estimates, suggests the presence of a long undocumented gap in the fossil record of opossums extending some 45Myr from the Early Miocene to the Cretaceous.