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Ichthyosaurs-The Dolphins of the Mesozoic

An Ichthyosaur

A fossilized ichthyosaur

A fossilized ichthyosaur

An illustration of an ichthyosaur from Berlin-Ichthyosaur Park in Nevada.

An illustration of an ichthyosaur from Berlin-Ichthyosaur Park in Nevada.

What are Ichthyosaurs?

Ichthyosaurs were marine reptiles that lived during the Mesozoic era, that is, the time of the dinosaurs.

They were similar to modern whales and dolphins in some ways. Ichthyosaurs (ick-thee-o-soars) or fish-lizards, lived on land, but returned to the water a little before the dinosaurs lived-probably around 250 million years ago.

In the oceans the ichthyosaurs' legs evolved into flipper-shapes and their tails became more like fish tails. They eventually developed to fill a similar biological niche as the modern day dolphins and whales.

Ichthyosaurs came in various sizes and versions, from the size of porpoises to enormous whale-like sizes as the Shonisaurus version on the right shows. Although the ichthyosaurs flourished for quite a long time, they went extinct around 90 million years ago, possibly due to getting out competed another marine predator, the plesiosaurs. Ichthyosaurs were interesting creatures and left intriguing fossils.

What caused the ichthyosaurs to go back to the sea, caused them to flourish for so long, and what caused them to die out, are all still mysteries, but what we do know is fascinating none the less.

Ichthyosaur - Natural History Museum of London

An Early Ichthyosaur Specimen

You can certainly tell why they were called Ichthyosaurs or "fish lizards"

You can certainly tell why they were called Ichthyosaurs or "fish lizards"

They Were Mesozoic Marine Reptiles

Ichthyosaurs lived for a long period of time a long time ago.

The Mesozoic is called the time of the dinosaurs and it ran from about 250 to 65 million years ago. Mesozoic means middle-life, and it is called so because it is the middle of the three main time periods of life on this planet, Paleozoic, Mesozoic, and Cenozoic (now).

The Mesozoic is the time period between two major extinctions too. The Permian-Triassic extinction event was the biggest extinction we know of on the planet, and the Cretaceous Extinction is the one we know of for killing off the dinosaurs.

Although the Mesozoic may be known as the time of the dinosaurs, most dinosaurs didn't really come on the scene in much of a big way until about 200 million years ago. The ichthyosaurs though started about 250 million years ago and lived until about 90 million years ago, so they survived in the seas for about 100 million years!

We don't know why they went extinct, but many think it's because other marine reptiles came on the scene and were too much competition.

A Fossil and a Model of How they Might Have looked

Is It a Dolphin?

Ichthyosaur at Boston Museum of Science

Ichthyosaur at Boston Museum of Science


This picture looks a lot like a dolphin doesn't it? If there wasn't a tag, you might actually think it was one, except there is something off. Though their bodies were really similar, dolphins and ichthyosaurs deviated on one important thing especially, their tails.

Dolphins, like most mammals, have tails that move up-and-down and that are wide. Ichthyosaurs, like fish and reptiles, have tails that move side-to-side and that are tall. Ichthyosaurs lived in the same place and filled the same biological niche as dolphins though, so it makes sense that they would seem similar, they lived very similar lives in some ways.

Evolving similar features like this is called evolutionary relay. "Evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems at different times-for example the dorsal fins of extinct ichthyosaurs and sharks." from Convergent Evolution

A Person and Smaller Ichthyosaur

Ichthyosaur Size

Ichthyosaurs varied a lot in size. Most were similar to dolphins, about 6 to 13 feet long. Some were very big though, up to 75 feet!

Can you imagine swimming in an ocean that had 75' predators in it?

Shonisaurus Type of Ichthyosaur

Voyage to Cretaceous Sea

Fossilized Ichthyosaur

Their Eyes

Ichthyosaurs are considered to have the biggest eyes ever known, proportionally. Their eyes were enormous and even if we were the size of an ichthyosaurs one of our eyes wouldn't even be as big as one of their pupils.

A Predator's Gaze

Can you picture this ichthyosaur soaring the ocean depths?

An Ichthyosaur in the Smithsonian National Museum of Natural History: Hall of Fossils

An Ichthyosaur in the Smithsonian National Museum of Natural History: Hall of Fossils

Flipper Development

Notice the toes of the ichthyosaur in the picture above. They've really spread out to make long flippers. They didn't start out like that though. When they first went back into the sea after being land reptiles, their toes and fingers were much like most creatures', shorter and angled for walking. As they spent more and more time in the water though, their flippers got longer and angled differently to push them through the ocean with more ease. The faster and better you swim, the more you can avoid predators and get food and eventually reproduce.

It's the same with whales and dolphins and manatees. When they were land mammals their toes were stubby and made for walking. The longer they spend in the sea the more they have elongated. No longer having to carry their own weight allows the toes to develop in a different direction and so instead they become more useful for swimming. Our hands used to be more like our toes, but when we started walking upright we were able to use our hands for more than supporting our weight and so our fingers became fingers and got longer.

Get Neptune's Ark: From Ichthyosaurs to Orcas

An Ichthyosaur Grin

A sharp grin

A sharp grin


You can tell what animals eat by what their teeth are like. Catching fish requires sharp, pointy teeth because they are so slippery. As you can see in the picture above, most ichthyosaurs had very sharp, pointed teeth, each one like a thick needle. That means they ate fish.

Some ichthyosaurs had slightly thicker teeth, less needle-like and more like pointed pegs. They probably ate something with a hard shell, like ammonites. The thicker teeth make the teeth more sturdy so they don't shatter when trying to bite harder things.

The shape of the jaw matters too. As some types of ichthyosaurs evolved to eat more fish, their jaws became longer and narrower while other types of ichthyosaurs had jaws that stayed massive and powerful for crushing force.

A Pointed Smile

Installing an Ichthyosaur in a Museum

Pregnant Ichthyosaur Fossil

Sea Monsters 3D: A Prehistoric Adventure

Below is the trailer for Sea Monsters 3D, a national Geographic movie about prehistoric marine reptiles. This movie follows a fossil discovered in Kansas and goes back in time to when that animal lived and tells her story. It really shows what the prehistoric seas would have been like though it is predominantly about plesiosaurs and mosasaurs.

Check out the link below video for purchasing information. The film is a bit short, but very intense and interesting and very well done.

Sea Monsters

This Ichthyosaur Seems Ready to Eat You Up

Berlin-Ichtyosaur State Park

In Central Nevada

Berlin Ichthyosaur State Park is composed of two parks in one. One section, the old mining town of Berlin is historic and a great way to view some of human history. The ichthyosaur section is a Registered Natural Landmark, and where one of the biggest ichthyosaur discoveries was ever made.

No one is quite sure of the entire story, it's difficult to discern clues from ages-old fossils, but the story of what might have happened to cause the ichthyosaurs to be at Berlin-Ichthyosaur State Park is:

Millions and millions of years ago, the west coast of what is now the United States was not where it is today. It was in the middle of Nevada, so the sea lapped over all of what is now California, and quite a bit of Nevada. These seas were rich in life, much as our seas are today. There were fish and predators and lots of small creatures. One of the predators of the time was the ichthyosaur, filling the niche that is now occupied by the whales and dolphins. They cruised the seas, looking for food, and possibly migrating as whales do today. There was a group of composed of 37 individuals of the largest type of ichthyosaur known to us, the Shonisaurus popularis. They came into the sea above what is now Nevada, why we don't know. Could they have been following food? Coming in the birth their young? On a migration route? We don't know, but for some reason, they were there.

This group of Shonisaurus came to a sudden demise. All of a sudden, they died and were buried, likely by an underwater landslide dropping tons of dirt upon them in a rapid burial of a massive degree. The Shonisaurus bodies buried under the pile were all overlapped, one carcass lying atop another. As time passed, more dirt built up over top of the Shonisaurus, and their bodies were fossilized. Millions of years later, the seas receded, the land rose, mountains formed, and eventually the coast came to be where it is now. Somewhere along the line, the burial location of the Shonisaurus became home to numerous small faults and the covering landscape started to be eroded away.

In 1928, Dr. Siemon Muller, discovered, in an exposed portion, the first fossils of what we now call Shonisaurus popularis. Berlin-Ichthyosaur State Park is in the boonies today, imagine it over eighty years ago! It was hard work in the heat and far away from any civilization, but excavations finally commenced in 1954 with Dr. Charles Camp directing them. Over 40 ichthyosaurs have been discovered in the area since.

For more information about Shonisaurus popularis, the type of ichthyosaur found at Berlin-Ichthyosaur State Park, check out this site: The Oceans of Kansas

Shonisaurus popularis Painting - Berlin-Ichthyosaur State Park

A life-sized painting done of Shonisaurus popularis, the type of ichthyosaur found at the Berlin-Ichthyosaur State Park in Nevada.

A life-sized painting done of Shonisaurus popularis, the type of ichthyosaur found at the Berlin-Ichthyosaur State Park in Nevada.

In 1984, Shonisaurus popularis became the State Fossil of Nevada

Visiting Berlin-Ichthyosaur Park

If you want to visit the Berlin-Ichthyosaur State Park you will want to plan ahead. It is located pretty much in the middle of nowhere, and while it is open year-around, extreme winter weather can prohibit travel. It is Nevada, so it can be dry and hot during the summer, though since the park is at 7,000' elevation, the temperature remains more moderate than most of Nevada, only reaching 90 degrees or so normally. It is covered in snow during the winter. Visiting the area in the fall or springtime is usually very nice and pleasant.

Many of the ichthyosaur fossils are housed on site, in situ, in the fossil house, tours are limited to the mid-spring, summer, and early-fall, so if you want to see the fossils, you have to come at the right time. The tour schedule varies, so contact the park to know when you should go, by calling (775) 964-2440. Also visiting Berlin-Ichthyosaur State Park website will give you more information.

On the Way to Berlin-Ichthyosaur Park

Inside the Fossil House - Berlin-Ichthyosaur State Park

Though it didn't show up well in the above picture, the fossil bed at Berlin-Ichthyosaur State Park is full of ichthyosaurs. Somehow, ichthyosaur bodies were piled up in this spot, perhaps buried by an underwater landslide, and the area was then buried even more and the bodies were fossilized. It's almost like a puzzle now, trying to figure out which parts go to which ichthyosaurs, since they are all overlaying each other and then the area was faulted, so the pieces aren't always next to where the other parts are.

Just recently a few scientists have come up with a hypothesis that the ichthyosaur bodies piled up at Berlin-Ichthyosaur State Park were actually part of a kraken lair. Giant Kraken Lair Discovered It's a rather novel idea, and a lot of research needs to be done before it's decided that actually is what caused the mass grave site.

Ichthyosaur Skull - Berlin-Ichthyosaur State Park

More ichthyosaur fossils inside the fossil house at Berlin-Ichthyosaur State Park.

More ichthyosaur fossils inside the fossil house at Berlin-Ichthyosaur State Park.

Sea Monsters 2 - Nothosaurs and Cymbospondylus - From Chased By Sea Monsters

The first sea creature shown the video below is a Nothosaur, but the second marine reptile is an ichthyosaur variety called Cymospondylus.

Static fossil pictures or recreations pale in comparison to these videos that mimic wildlife shows and show how the creatures may have looked, behaved, and swam. Check out the link below the video for more information on purchasing the complete video this segment was taken from. It's really very interesting and even people not into science like watching this movie.

Chased By Sea Monsters

An Ichthyosaur in the the Smithsonian

A Sea Dragon?

Doesn't the picture above look a lot like popular images of sea monsters, sea dragons, and so on?

Many people believe tales of sea monsters came about when people found fossils of ichthyosaurs and other marine reptiles. Long ago, people didn't know what extinction meant or that there were creatures that lived long before mankind. They thought if they found the bones of something it meant it was still alive out there somewhere.

Get Ichthyosaurs: A History of Fossil Sea-dragons


Monster Fish: The Adventure of the Ichthyosaurs

Ichthyosaur Fossil

More Information on Ichthyosaurs

Learn More About Ichthyosaurs

© 2009 Alisha Vargas

What Do You Think of Ichthyosaurs?

TobyFugitt on September 17, 2012:

I love dinosaurs!

HomeDecorKnight on September 17, 2012:

Nice lens. I saw a awesome picture and video about Ichthyosaurs.I like the lens.

MrTossot on January 28, 2012:

ha ha ha! the first picture is so funny

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