Elucidating how body parts in their earliest recognizable form are assembled in tetrapods during development is essential for understanding the nature of morphological evolution. Researchers found in eight tetrapod species that the position of the sacral vertebrae and the hindlimbs is determined by the initiation timing of Gdf11 gene expression. This will contribute to a forthcoming model explaining the coupling of spine and hindlimb positioning – a major step in fully understanding tetrapod evolution.