Biology subjects

Amson, E.

Publications and source records attributed to Amson, E..

3 recordsLinked to original sources

bioRxiv2020

Evolution of bone cortical compactness in slow arboreal mammals

Lifestyle convergences and related phenotypes are a major topic in evolutionary biology. Low bone cortical compactness (CC), shared by the two genera of tree sloths, has been linked to their convergently evolved slow arboreal ecology. The proposed relationship of low CC with tree sloths lifestyle suggests a potential convergent acquisition of this trait in other slow arboreal mammals. Tree sloths, Lorisidae, Palaeopropithecidae, Megaladapis and koalas were included in a phylogenetically informed CC analysis of the humerus and femur, as well as closely related but ecologically distinct taxa. We found that tree sloths are unparalleled by any analysed clade, in featuring an extremely low CC. A tendency for low CC was however found in palaeopropithecids (especially Palaeopropithecus) and Megaladapis. On the other hand, low CC was not found in Lorisidae. Koalas, although deviating from the compact structure generally observed in mammals, are not clearly distinct from their sister taxon (wombats) and show humeral CC that is higher than femoral CC. Multiple factors seem to influence CC, preventing the recognition of a simple relationship between slow arborealism and low CC. Highly compact cortical bone in extinct sloths confirms that low CC in tree sloths likely represents a recent convergence.

evolutionary biology↗

bioRxiv2020

Differing effects of size and lifestyle on bone structure in mammals

The skeleton is involved in most aspects of vertebrate life history. Previous macroevolutionary analyses have shown that structural, historical, and functional factors influence the gross morphology of bone. The inner structure of bone has, however, received comparatively little attention. Here we address this gap in our understanding of vertebrate evolution by quantifying bone structure in appendicular and axial elements (humerus and mid-lumbar vertebra) across therian mammals (placentals + marsupials). Our sampling captures all transitions to aerial, fully aquatic, and subterranean lifestyles in extant mammal clades. We found that mammalian inner bone structure is highly disparate. We show that vertebral structure mostly correlates with body size, but not lifestyle, while the opposite is true for humeral structure. The latter also shows a high degree of convergence among the clades that have acquired specialised lifestyles. Our results suggest that radically different extrinsic constraints can apply to bone structure in different skeletal elements.

evolutionary biology↗

bioRxiv2018

Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia)

Trabecular architecture (i.e., the main orientation of the bone trabeculae, their number, mean thickness, spacing, etc.) has been shown experimentally to adapt with great accuracy and sensitivity to the loadings applied to the bone during life. However, the potential of trabecular parameters used as a proxy for the mechanical environment of an organisms organ to help reconstruct the lifestyle of extinct taxa has only recently started to be exploited. Furthermore, these parameters are rarely combined to the long-used mid-diaphyseal parameters to inform such reconstructions. Here we investigate xenarthrans, for which functional and ecological reconstructions of extinct forms are particularly important in order to improve our macroevolutionary understanding of their main constitutive clades, i.e., the Tardigrada (sloths), Vermilingua (anteaters), and Cingulata (armadillos and extinct close relatives). The lifestyles of modern xenarthrans can be classified as fully terrestrial and highly fossorial (armadillos), arboreal (partly to fully) and hook-and-pull digging (anteaters), or suspensory (fully arboreal) and non-fossorial (sloths). The degree of arboreality and fossoriality of some extinct forms, \"ground sloths\" in particular, is highly debated. We used high-resolution computed tomography to compare the epiphyseal 3D architecture and mid-diaphyseal structure of the forelimb bones of extant and extinct xenarthrans. The comparative approach employed aims at inferring the most probable lifestyle of extinct taxa, using a phylogenetically informed discriminant analysis. Several challenges preventing the attribution of one of the extant xenarthran lifestyles to the sampled extinct sloths were identified. Differing from that of the larger \"ground sloths\", the bone structure of the small-sized Hapalops (Miocene of Argentina), however, was found as significantly more similar to that of extant sloths, even when accounting for the phylogenetic signal.

paleontology↗