Whales: Macroevolutionary Change In Whale Evolution
The origin of whales (order Cetacea) is one of the best-docu- mented examples of macroevolutionary change in vertebrates1–3. As the earliest whales became obligately marine, all of their organ systems adapted to the new environment. The fossil record indicates that this evolutionary transition took less than 15 million years, and that different organ systems followed different evolutionary trajectories. Here we document the evolutionary changes that took place in the sound transmission mechanism of the outer and middle ear in early whales. Sound transmission mechanisms change early on in whale evolution and pass through a stage (in pakicetids) in which hearing in both air and water is unsophisticated. This intermediate stage is soon abandoned