New Findings at Andrahomana Cave, Southeastern Madagascar

A remote eolianite cave and sinkhole complex on the southeast coast of Madagascar has played a major role in the history of paleontology in Madagascar. Andrahomana Cave has yielded a rich fossil record of the extinct megafauna. Expeditions in 2000 and 2003 produced a wealth of new material and provided the first systematic information concerning the genesis, stratigraphy, and taphonomy of the site. Recovered bones of one of the most poorly understood extinct large lemurs, Hadropithecus stenognathus, include many skeletal elements previously unknown. Radiocarbon dates show that the site has sampled this disappeared fauna in the midto- late Holocene, but that bone-bearing layers are stratigraphically mixed, probably owing to the effects of reworking of the sediments by extreme marine events. The diverse biota recovered contains elements of both eastern rain forest and southwestern arid bushland, reflecting the cave’s position in the zone of transition between wet and dry biomes. Bones of two unusual small mammals add to the previously long faunal list for the site: 1) the first fossil evidence for Macrotarsomys petteri, a large-bodied endemic nesomyid rodent previously known only from a single modern specimen; and 2) the type specimen and additional material of a newly described extinct shrew-tenrec (Microgale macpheei). Evidence for prehistoric and colonial-era humans includes artifacts, hearth deposits, and remains of human domesticates and other introduced species. Although previously protected by its extreme isolation, the unique site is vulnerable to exploitation. An incipient tourist industry is likely to bring more people to the cave, and there is currently no form of protection afforded to the site

Microstructure and mechanical behavior of superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N biomedical alloys

International audienceIn this study, the microstructure and the mechanical properties of two new biocompatible superelastic alloys, Ti-24Nb-0.5O and Ti-24Nb-0.5N (at.%), were investigated. Special attention was focused on the role of O and N addition on α″ formation, supereleastic recovery and mechanical strength by comparison with the Ti-24Nb and Ti-26Nb (at.%) alloy compositions taken as references. Microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy before and after deformation. The mechanical properties and the superelastic behavior were evaluated by conventional and cyclic tensile tests. High tensile strength, low Young's modulus, rather high superelastic recovery and excellent ductility were observed for both superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N alloys. Deformation twinning was shown to accommodate the plastic deformation in these alloys and only the {332}〈113〉 twinning system was observed to be activated by electron backscattered diffraction analyses

Elaboration et caractérisation d'alliages de type Ti-Nb-X (X = O, N) pour des applications biomédicales Synthesis and characterisation of Ti-Nb-X (X = O, N) alloys for biomedical application

Dans cette étude, trois alliages de titane β-métastables de composition Ti-27Nb, Ti-24Nb-0.5N et Ti-24Nb-0.5O ont été élaborés par fusion. Ces trois alliages présentent des propriétés superélastiques lors des essais de traction. Des essais de traction in-situ sous rayonnement synchrotron nous ont permis de monter que cette superélasticité est due à une transformation martensitique réversible β → α” bien connue pour deux alliages alors que celui contenant de l'oxygène présente un comportement moins conventionnel. Les températures caractéristiques (MS, MF) de la transformation martensitique β (austénite) vers α” (martensite) et celles (AS, AF) de la transformation inverse α” vers β ont aussi été déterminées par des essais mécaniques dynamiques. Ces températures caractéristiques augmentent linéairement avec la contrainte externe et cette augmentation suit la relation de Clausius Clapeyron. <br> Ti-Nb based alloys are well known to their good mechanical properties, shape memory effect, superelasticity, as well as good biocompatibility. Our study is focused on the improvement of their mechanical properties by adding alloying element such as oxygen or nitrogen. Superelasticity was drastically improved by addition of a few amount (0.5 at %) of oxygen or nitrogen. Martensitic transformation between the β parent phase (austenite) and α” product phase (martensite), responsible for the superelastic property, has been extensively studied by Dynamic Mechanical Analysis (DMA) and in-situ tensile test under X-ray synchrotron diffraction

Synthesis and characterization of new superelastic and low elastic modulus Ti-Nb-X alloys for biomedical application.

International audienceTi-Nb based alloys are well known to their good mech. properties, shape memory effect, superelasticity, as well as good biocompatibility. The Ti-24Nb (at%) binary alloy presents a shape memory behavior and low elastic modulus. Our study is focused on the improvement of their mech. properties by adding a third alloying element (oxygen, nitrogen or silicon). Addn. of 0.5 at% of N or O modifies drastically the mech. behavior of Ti-24Nb alloy that exhibits superelastic behavior instead of shape memory one. On the other hand, addn. of 0.5 at% of Si increased yield strength of the Ti-24Nb shape memory alloy. [on SciFinder(R)

In situ synchrotron X-ray diffraction study of the martensitic transformation in superelastic Ti-24Nb-0.5N and Ti-24Nb-0.5O alloys.

International audienceMechanisms of superelasticity were investigated by in situ cyclic tensile tests performed under synchrotron X-ray radiation on Ti-24Nb-0.5N and Ti-24Nb-0.5O compns. of metastable β titanium alloys. Analyses of diffraction patterns acquired under load and after unloading for each cycle were used to det. the characteristics of the potential mechanisms of deformation in both alloys. The Ti-24Nb-0.5N alloy exhibits the conventional behavior of superelastic β titanium alloys. Synchrotron X-ray diffraction (SXRD) expts. proved that superelasticity is exclusively due to the occurrence of a stress-induced martensitic (SIM) transformation from the β phase to the α'' phase. The evolution of vol. fraction of α'' martensite corresponds exactly to the variation of the recovery strain of the cyclic tensile curve. Conversely, the Ti-24Nb-0.5O alloy displays a non-conventional behavior. SXRD expts. showed a huge ability of the β phase to deform elastically until 2.1%. Surprisingly, a reversible SIM transformation also occurs in this alloy but starts after 1% of applied strain that corresponds to the yield point of the stress-strain curve. Although the SIM transformation occurs, the β phase simultaneously continues to deform elastically. The superelasticity of this alloy is unexpectedly due to a combination of a high elastic deformability of the β phase and a reversible SIM transformation. In both alloys, the lattice parameters of the α'' martensite evolve similarly in accordance with the initial texture of the β phase and the crystallog. of the transformation

New Discoveries of the Skeletal Elemnts of Hadropithecus stenognathus from andrahomana Cave, Southeastern Madagascar

Remains of what appears to be a single, subadult Hadropithecus stenognathus were recovered from a previously unexcavated site at Andrahomana Cave (southeastern Madagascar). Specimens found comprise isolated teeth and cranial fragments (including the frontal processes of the orbits), as well as a partial postcranial skeleton. They include the first associated fore- and hind-limb bones, confirming the hind-limb attributions made by Godfrey and co-workers in 1997, and refuting earlier attributions by Lamberton in 1937/1938. Of particular interest here are the previously unknown elements, including a sacrum, other vertebrae and ribs, some hand bones, and the distal epiphysis of a femur. We briefly discuss the functional implications of previously unknown elements. Hadropithecus displayed a combination of characters reminiscent of lemurids, others more like those of the larger-bodied Old World monkeys, and still others more like those of African apes. Yet other characteristics appear unique. Lemurid-like postcranial characteristics may be primitive for the Archaeolemuridae. Hadropithecus diverges from the Lemuridae in the direction of Archaeolemur, but more extremely so. Thus, for example, it exhibits a stronger reduction in the size of the hamulus of the hamate, greater anteroposterior compression of the femoral shaft, and greater asymmetry of the femoral condyles. Nothing in its postcranial anatomy signals a close relationship to either the Indriidae or the Palaeopropithecidae