10 Prehistoric Fish Everyone Should Know

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Are You Familiar With These 10 Prehistoric Fish?

Wikimedia Commons.

Fish have the longest evolutionary history of any vertebrates on earth--for the simple reason that fish were the very first vertebrates to evolve on earth! On the following pages, you'll discover 10 prehistoric fish, stretching over 500 million years, that marked important evolutionary advances in this populous breed--as the first primitive species gradually acquired jaws, solid skeletons, and other key adaptations that have allowed them to thrive down to the present day.


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Haikouichthys (530 Million Years Ago)

Haikouichthys (Wikimedia Commons).

One of a trio of important Cambrian marine organisms--the other two being Pikaia and Myllokunmingia--Haikouichthys was one of the first animals on earth to possess a skull and (possibly) a semi-solid backbone protecting the delicate notochord that ran down its back. Haikouichthys also exhibited all the (now unremarkable) hallmarks of vertebrate life, including bilateral symmetry and a head with two eyes. It may be a stretch to call it a true fish, but it was certainly just an evolutionary stone's throw away.


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Arandaspis (480 Million Years Ago)

Arandaspis (Getty Images).

The only thing barring the classification of Haikouichthys (see previous slide) as a true fish its its lack of a backbone, but no such objection can be raised to Arandaspis, which lived about 30 million years later and had an unmistakable set of vertebra protecting its spinal cord. Like the other "-aspis" fish of the middle Paleozoic Era (including Astraspis and Doryaspis), the six-inch-long Arandaspis lacked movable jaws, and its body was covered with a protective layer of tough, bony armor plating.


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Entelognathus (420 Million Years Ago)

Entelognathus (Brian Choo).

The name Entelognathus means "perfect jaw," and that's all you need to know about why this recently discovered fish has been included on this list. Recently discovered in China, in sediments dating back to the Silurian period, Entelognathus possessed a set of primitive jaws, a huge evolutionary advance over jawless fishes like Arandaspis (see previous slide). Not only did this make Entelognathus a more efficient predator, but it also set the pattern for over 400 million years of subsequent fish (and vertebrate) evolution.


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Dunkleosteus (380 Million Years Ago)

Dunkleosteus (Wikimedia Commons).

Just how important was the evolution of jawed fish during the Silurian period? Well, fast-forward ahead about 40 million years, to the late Devonian, and you'll find Dunkleosteus, a 30-foot-long, four-ton armored behemoth with a set of jaws worthy of Tyrannosaurus Rex (albeit lacking any teeth). As the apex predator of its briny ecosystem, Dunkleosteus had nothing to fear from much smaller sharks like Cladoselache; in fact, that only thing that could harm a Dunkleosteus was another Dunkleosteus, as these giant fish were occasional cannibals.


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Saurichthys (250 Million Years Ago)

Saurichthys (Wikimedia Commons).

Not to be confused with Ichthyosaurus ("fish lizard")--a roughly contemporary marine reptile--Saurichthys ("lizard fish") was one of the first ray-finned fish, as distinct from the lobe-finned fish that preceded it. Why is this important? Well, lobe-finned fish went on to spawn the first tetrapods--which spearheaded the vertebrate colonization of dry land--while ray-finned fish were fated to dominate the world's oceans. Today, in fact, ray-finned fish are some of the most diverse vertebrates on the planet, rivaled only by birds.


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Leedsichthys (150 Million Years Ago)

Leedsichthys (Dmitry Bogdanov).

By some estimates the largest fish that ever lived, Leedsichthys measured anywhere from 30 to 70 feet from head to tail and weighed between five and 50 tons (this wide range can be attributed to the numerous partial fossils of this Jurassic fish, which don't add up to a single convincing picture). Like its fellow behemoth, the Blue Whale, the giant Leedsichthys fed on tiny plankton--this fish was equipped with over 40,000 interlocking teeth, which created a mesh structure similar to baleen (a much later evolutionary development).


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Xiphactinus (90 Million Years Ago)

Xiphactinus (Wikimedia Commons).

After the monstrous Leedsichthys (see previous slide), the fish of the Mesozoic Era had nowhere to go but down. Any fisherman worth his salt would boast about catching the 20-foot-long, half-ton Xiphactinus, but the fact was that this late Cretaceous fish was at the mercy of fierce sharks like Squalicorax and Cretoxyrhina (in whose stomachs have been found the fossilized remnants of half-eaten Xiphactinus). It's nothing to be proud of, but Xiphactinus marked the point in evolutionary history when fish ceded pride of place to their close cousins, the sharks.


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Knightia (55 Million Years Ago)

Knightia (Nobu Tamura).

Not only should everyone know about Knightia; you can also own your very own Knightia, since this fossil fish is so common that complete specimens can be had for as little as a couple of hundred bucks. Knightia can be considered the first "fishy" fish on this list, a tiny, herring-sized plankton eater that assembled in vast schools in the shallow waters covering Eocene North America. In fact, Knightia is one of the state fossils of Wyoming, the other being the much more famous (and slightly earlier) Triceratops.

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The Megapiranha (10 Million Years Ago)

Contemporary piranhas are no match for the Megapiranha (Wikimedia Commons).

Not only mammals came in larger sizes during the Cenozoic Era: the same can be said about various prehistoric fish, chief among them the aptly named Megapiranha. Although the Megapiranha wasn't nearly the size of the contemporary shark Megalodon--only about five feet long and 25 pounds--it was still an order of magnitude larger than any piranha alive today. What's more, the Megapiranha could chomp down on its prey with a force of 1,000 pounds per square inch, putting it in the same weight class as the much bigger T. Rex.


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The Coelacanth (Still Extant)

A Coelacanth (Wikimedia Commons).

Why include a still-extant fish on this list? Well, for over a century, the lobe-finned fish known as Coelacanths were thought to have been extinct since the Cretaceous period--until two separate living individuals were dredged up near the coasts of South Africa and Indonesia. The lesson here is that the oceans are inconceivably vast, and our knowledge of the fish that ply them is woefully incomplete. Don't be surprised if another supposedly "extinct" fish is discovered in the Marianas Trench, or some other previously inaccessible part of the deep!

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Strauss, Bob. "10 Prehistoric Fish Everyone Should Know." ThoughtCo, Apr. 2, 2015, thoughtco.com/prehistoric-fish-everyone-should-know-1093345. Strauss, Bob. (2015, April 2). 10 Prehistoric Fish Everyone Should Know. Retrieved from https://www.thoughtco.com/prehistoric-fish-everyone-should-know-1093345 Strauss, Bob. "10 Prehistoric Fish Everyone Should Know." ThoughtCo. https://www.thoughtco.com/prehistoric-fish-everyone-should-know-1093345 (accessed November 18, 2017).