Here's why:
* Fish breathe underwater using gills. Great white sharks, like all fish, have gills that extract oxygen from water.
* Mammals breathe air using lungs. They have lungs that allow them to breathe air from the atmosphere.
* Fish are cold-blooded. Their body temperature changes with the temperature of their surroundings.
* Mammals are warm-blooded. They maintain a constant internal body temperature.
* Fish reproduce by laying eggs.
* Mammals give birth to live young.
Great white sharks may be large and powerful, but they are ultimately fish, and share many characteristics with other fish species.