The secondary adaptation to an aquatic life Contribution of bone microstructure – AQUABONE

Organisms are subjected to both intrinsic and extrinsic constraints during their life-time as well as in an evolutionary context. According to the constructional morphology model of Seilacher (Seilacher, 1970; Gould, 2002; Cubo, 2004), biological features are considered as the outcome of phylogenetic, adaptative, and architectural constraints, referred to as historical, functional, and structural constraints by Gould (2002). This is also the case for bone microanatomical and histological features, i.e. the internal organization of bone and the specific features of the osseous tissues. Bone is a living structure and thus records information about the biology and ecology of the organisms (e.g. type and speed of growth, age at sexual maturity, life history, physiology, mechanical constraints, etc...). Bone is, in fact, a very plastic structure. Thus, microanatomical specializations are thought to occur before large-scale anatomical ones, such that bone microanatomy can be used as a tool to understand the initial stages of adaptation to, for example, a new environmental context (e.g. aquatic versus terrestrial).

The adaptation to specific environments has happened several times independently in various lineages of tetrapods. If several of the associated features are nowadays observable in modern forms, fossil taxa are essential to complete our knowledge and in order to understand the evolutionary processes involved. The current project proposes to focus on secondary adaptation to an aquatic life in amniotes and, more specifically on the adaptations to a semi-aquatic life style in mammals.

By linking microanatomical specializations with the specific functional requirements of locomotion in semi-aquatic amniotes using available ecological data and in vivo studies we aim to gain insights on the ecology of fossil taxa. More specifically, we aim to understand transitional forms in the process of a secondary adaptation to an aquatic life and the different steps of adaptation to this new milieu in different lineages. The larger objective is to understand the adaptation of bone to intrinsic (e.g. phylogenetic, behavioural) and extrinsic (e.g. environmental) constraints in the process of secondary adaptation to an aquatic life, a major theme in evolutionary biology.