Prehistoric Fish and Marine Mammal Biology
The first prehistoric fish appeared about 530 million years ago. These prehistoric fish were the first vertebrates. They appeared during the Cambrian Period. The Haikouichthys was one of these first fish. They were jawless and similar to the lampreys of today.
About 430 million years ago, armored fish began to appear. The Dunkleosteus was an armored predator that could reach a length of 10 meters.
The spiny sharks, such as Acanthodes, appeared about 400 million years ago. The Dipterus was a lobe-finned lungfish that appeared about 376 million years ago. Both of these fish have characteristics of the bony and cartilaginous fish.
True cartilaginous fish appeared about 260 million years ago. The Hybodus was a prehistoric shark that grew to a length of 2 meters. Although extinct, they resemble the modern sharks of today.
The ray-finned fish appeared about 145 million years ago. The Enchodus were small predator fish with large fang-like teeth. It was a bony fish.
Prehistoric Marine Mammals
Marine mammals appeared about 55 million years ago. Eobalaenoptera was a whale that grew to a length of about 11 meters. The Basilosaurus grew to a length of 20 meters.
The prehistoric fish and marine mammals are all vertebrates and belong to the phylum Chordata. Although extinct, most have species descended from them that are alive today.
The prehistoric fish and marine mammals lived all over the globe – from deep ocean waters to shallow inland seas.
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Fish Evolution, About.com