Fish, Shrimp & Jellyfish - Shoplivepages::jquery();?>
Compared to dinosaurs, mammoths and saber-toothed cats, fish evolution may not seem all that interesting--until you realize that if it weren't for prehistoric fish, dinosaurs, mammoths and saber-toothed cats would never have existed. The first vertebrates on the planet, fish provided the basic "body plan" subsequently elaborated on by hundreds of millions of years of evolution.
During the Ordovician and Silurian periods--from 490 to 410 million years ago--the world's oceans, lakes and rivers were dominated by jawless fish, so named because they lacked lower jaws (and thus the ability to consume large prey).
By the start of the Devonian period--about 420 million years ago--the evolution of prehistoric fish veered off in two (or three, depending on how you count them) directions. One development, which wound up going nowhere, was the appearance of the jawed fishes known as placoderms ("plated skin"). These were essentially larger, more varied "-aspis" fish with true jaws, and the most famous genus by far was the 30-foot-long Dunkleosteus, one of the biggest fish that ever lived.
No history of fish would be complete without mentioning the giant "dino-fish" of the Triassic, Jurassic and Cretaceous periods (though these fish weren't as numerous as their oversized dinosaur cousins). The most famous of these giants were the Jurassic Leedsichthys, which some reconstructions put at a whopping 70 feet long, and the Cretaceous Xiphactinus, which was "only" about 20 feet long but at least had a more robust diet (other fish, compared to Leedsichthys' diet of plankton and krill).