Early evolution of growth and physiology during the mammal-reptile split using phase contrast tomography of unique fossil specimens

Amniotes (land vertebrates) include mammals and reptiles, encompassing a vast range of ecologies, physiologies, and life histories from fast-growing homeothermic endotherms (mammals and birds) to slow-growing poikilothermic ectotherms (non-avian reptiles). All living amniotes share a common ancestor that lived over 300 million years ago. However, very little is known of the growth and physiology of this ancestor, because traditional methods to study bone tissue microstructure are destructive and cannot be applied to rare or tiny fossils. We aim to use synchrotron X-ray phase-contrast micro computed tomography to reveal bone tissue microstructure of the earliest amniote fossils and their ancestral (stem) lineage, providing unprecedented information on the life history and growth rates of the earliest amniotes. This experiment will address a fundamental question of vertebrate evolution, providing novel insights into the evolution of growth patterns during the mammal-reptile split.