9781422279151

Ocean Evolution A bout 50 million years ago, things on land were getting tough. Mammals had evolved from amphibians and reptiles and their populations on land were growing larger and stronger. As they did, the competition for food and re- sources got more intense. The situation was different in the ocean. At that time, the oceans were becoming easier to get to as the continents slowly drifted apart. That created large areas of open water and more coastline. The ocean was also packed with fish

and other creatures, making it a great source of food. Land-based mammals just had to “figure out” how to take advantage of it. Grad- ually, some land mammals began to adapt to living in water, and they evolved into the marine mammals seen today. Marine mammals have certain characteristics that make them ideal for living

Coral reefs are made from animal skeletons.

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