25 Incredible Sea Monsters That Once Ruled The Oceans

Posted by , Updated on December 16, 2017


Have you ever wondered what swam in Earth’s oceans millions of years ago? Things were much different then. Humans weren’t around, so we didn’t have to worry about being devoured by gargantuan monsters swimming in the deep. A big part of North America was covered in water called the Western Interior Seaway, brimming with predatory reptiles. These sea creatures were gigantic, fierce, and had razor sharp teeth, but there’s still a lot we don’t know about them. Curious to find out what we do know? These are 25 incredible sea monsters that once ruled the oceans.



PikaiaSource: http://paleobiology.si.edu/burgess/pikaia.html

While not exactly a “dinosaur,” Pikaia is one of the earliest creatures swimming around in the Burgess Shale community and has a direct link as one of humanities earliest ancestors.



ichthyosaursSource: http://www.ucmp.berkeley.edu/diapsids/ichthyosauria.html

Meaning “Fish Lizard,” Ichthyosaurs shared the sea with several large dinosaurs at the time. They originally swam like eels but advanced into looking and swimming like a modern day fish or dolphin. Like modern whales, they breathed air and lacked gills but could give birth in the water.



ShastasaurusSource: http://www.prehistoric-wildlife.com/species/s/shastasaurus.html; https://www.newdinosaurs.com/shastasaurus/

Located in California, British Columbia, and China, the Shastasaurus was a massive sea creature, measuring up to 21 meters long. In fact, it’s considered to be the largest marine reptile to ever live. In spite of it’s size, Shastasaurus primarily lived off of small fish, cephalopods, and squids.



pliosaurSource: http://www.bbc.co.uk/nature/life/Pliosaur

Built for speed, the Pliosaur had a short neck and could swim up to 10 km/h. They hunted fish, cephalopods, and other marine reptiles but have been found to also have land dinosaur remains in their stomachs.



ThalassomedonSource: http://www.prehistoric-wildlife.com/species/t/thalassomedon.html

Found in Colorado and Montanna, the Thalassomedon has a long neck and was only known in the Late Cretaceous due to other predators taking over.

Photo: 25. Nobu Tamura (http://spinops.blogspot.com), Pikaia BW, CC BY 3.0, 24. Pixabay.com (Public Domain), 23. Nobu Tamura (http://spinops.blogspot.com), Shastasaurus BW, CC BY 3.0, 22. John Cummings, Pliosaur, Rhomaleosaurus camptoni, Natural History Museum, London, CC BY-SA 3.0, 21. Nobu Tamura (http://spinops.blogspot.com), Thalassomedon BW, CC BY-SA 3.0, 20. Creator:Dmitry Bogdanov, Squalicorax2DB, CC BY 3.0, 19. Julian Johnson, Xiphactinus CGI, CC BY-SA 2.0, 18. Durbed, Dakosaurus, Cricosaurus, and ichthyosaurs by durbed, CC BY-SA 3.0, 17. Wikipedia Commons.com (Public Domain), 16. Creator: Dmitry Bogdanov, Tylosaurus pembinensis 1DB, CC BY 3.0, 15. Apokryltaros, Megapiranha Colossoma, CC BY-SA 4.0, 14. Wikipedia Commons.com (Public Domain), 13. Model created by Adam Procházka, Baden-Baden, Germany for Staatliches Museum für Naturkunde Karlsruhe, Germany. Foto: H. Zell, Nothosaurus mirabilis 01, CC BY-SA 3.0, 12. Nobu Tamura (http://spinops.blogspot.com), Otodus obliquus, CC BY 3.0, 11. Ghedoghedo, Tanystropheus longobardicus 4, CC BY-SA 3.0, 10. Nobu Tamura (http://spinops.blogspot.com), Stethacanthus BW, CC BY 3.0, 9. Ghedoghedo, Bernissartia fagesii, CC BY-SA 3.0, 8. Wikipedia Commons.com (Public Domain), 7. DiBgd, Thalattoarchon DB15, CC BY-SA 4.0, 6. Nobu Tamura (http://spinops.blogspot.com), Shonisaurus BW 2, CC BY-SA 3.0, 5. Ghedoghedo, Mosasaurus beaugei skull, CC BY-SA 4.0, 4. Nobu Tamura (http://spinops.blogspot.com), Liopleurodon BW, CC BY-SA 3.0, 3. Nobu Tamura (http://spinops.blogspot.com), Cymbospondylus BW, CC BY-SA 3.0, 2. Wikipedia Commons.com (Public Domain), 1. Karen Carr, VMNH megalodon, CC BY 3.0

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