How to make a limb: an evolutionary perspective using state-of-the-art three-dimensional imaging

The appearance of the tetrapod limb is a crucial event dated from about 400 million years ago. It has obviously played a crucial role in the move of tetrapods on land and their successful radiation. The tetrapod limb derives from the fin of a lobe-finned fish.

Transforming a fin to a limb profoundly affects the 3D architecture of the appendage at both morphological and histological levels.

For example, during the early evolution of tetrapods, the haematopoietic (blood cell-producing) tissue transferred to the bone marrow.

The reasons and underlying processes for this fin-to-limb transition are still unclear, partly because traditional palaeontological techniques have not been able to uncover the crucial changes in 3D microarchitecture associated with these extraordinary new functionalities.

I will address this issue using a novel cross-disciplinary approach based on state-of-the-art three-dimensional imaging techniques at high resolution, combined with evidence of biomarkers, to provide the first comprehensive picture of two major steps in the limb evolution: 1) the shaping of our limb into three segments and 2) the origin of blood-cell production in limb bones.

This project will enlighten this obscure but critically important event in the tetrapod evolutionary history and illuminate the process by which our limb skeleton became, not just a locomotory element, but an essential source of cell manufacture without which we cannot survive.