A scientist examines the two animals shown below and concludes that they must have shared a common ancestor at some point. Based on your understanding of homologous structures, determine whether his conclusion is valid. Explain your reasoning.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.