Heterochronic activation of TGF-β signaling drives the diversity of the avian sterna (opens in new tab)

Adaptive evolution has shaped vertebrate skeletal morphology, supporting diverse locomotor modes and lifestyles. In volant birds (carinates), the sternum develops a ventral keel for the attachment of massive pectoral muscles essential for powered flight. In contrast, flightless ratites lack both flight and the keel, creating a marked contrast in sternal shape. Here, we interrogated the cellular and molecular basis underlying this divergence using chicken and emu embryos as models. Through a s...