The Ichthyosaurs is an order of dinosaur meaning “fish lizard”. They were giant marine reptiles that resembled dolphins and fish. Based on fossil evidence, they thrived during the Mesozoic era and first appeared about 245 million years ago and disappeared only about 90 million years ago – 25 million years before the dinosaurs became extinct. During the middle Triassic period, Ichthyosaurs evolved from unidentified land reptiles that moved back into the water that is a development parallel to modern-day dolphins and whales. They were abundant during the Jurassic period, until they were knocked off their perch as the top aquatic predator by the plesiosaurs in the Cretaceous period.
Ichthyosaurs were small, with an average of 2 to 4 meters in length. However, some were smaller and some grew a lot larger than 4 meters They had a porpoise-like head with a toothed and long snout. They were speedy creatures like the modern-day tuna, and some Ichthyosaurs were deep divers like today’s modern whales. It is thought that these ‘fish lizards’ could swim up to speeds of 40 kilometers per hour (25 miles per hour). Like modern day cetaceans like dolphins and whales, they were breathed air.
Although the Ichthyosaurs looked like fish, they are not fish. A Biologist called Stephen Jay Gould claims that the Ichthyosaur were his favorite example of convergent evolution. This is because they converged strongly on fish that it evolved a dorsal fin. This plus the tail are in the ‘right’ place with the ‘right’ design. He says that it is amazing as they did not evolve from anything – no other ancestral terrestrial reptile had a humped back or a tail with a blade.
This seems to be quite true, because early reconstructions of the Ichthyosaurs did not include the dorsal fin. The dorsal fin does not have a hard skeletal structure, until extremely well preserved specimens found in Germany in the 1890’s revealed traces of such a fin. This was due to unique conditions which preserved soft tissue impressions.
For food, the Ichthyosaurs ate on ancient cephalopods called belemnites, which are the ancestor of modern-day squids. Some Ichthyosaurs also had teeth that were adapted to crushing shellfish. They also are thought to have eaten fish, and some of the larger Ichthyosaurs may have eaten small reptiles due to their heavy jaws and teeth. The Ichthyosaurs have very large eyes that are protected within a bony ring, which suggests they may have hunted during the night time.
The Ichthyosaurs have been featured in popular culture. In Jules Verne’s famous book, Journey to the Center of the Earth, it mentions the Ichthyosaurs as one of the prehistoric creatures. In this book, it rights with a Plesiosaurus. In the video game, Half-Life, the Ichthyosaurs is a large aquatic monster. They Might Be Giants created a song called “Nine Bowls of Soup” which is about an Ichthyosaur that carried too much soup. Obviously, for all 3 examples of the Ichthyosaurs in popular culture, they were not entirely factual or bore any resemblance to a real Ichthyosaurs.
Though related, it’s technically not a dinosaur.
A painting of the Ichthyosaur by H. Harder