Ichthyosaurs were aquatic reptiles that resembled dolphins that lived 160 million years ago in the Mesozoic era. Their name Ichthyosaur is derived from 2 ancient Greek words, “ichthys” meaning fish, and “sauros” meaning lizard, combined together to form “fish lizard.” For most prehistoric vertebrates, petrified teeth, and bones are the main sources of information on these well-known creatures.

Their history reveals a fast-evolving collection of creatures that were capable of reaching vast sizes and that shared a body form with whales and dolphins as a result of their adaptation to pelagic settings.


Ichthyosaurus was around 6-10 ft long and could possibly move at great speeds across the water. Ichthyosaurs were most likely dark brown with countershading properties; this is a typical tactic used by pelagic animals to conceal themselves in open waters by lowering the geometrical contour of their bodies.

The head merged seamlessly into the torso, and the body would extend seamlessly with no obvious neck. The Ichthyosaurs’ limbs were transformed into paddle-like appendages for superior mobility underwater. Alongside a well-developed fish-like tail and body, undulations served as its means of propulsion.

Closeup of a Ichthyosaurs fossil with notable snout, and eye size
Closeup of a Ichthyosaurs fossil with notable snout, and eye size

Ichthyosaurus had huge jaws and a long, long head that was packed with rows of sharp teeth. Some scholars suggest that these reptiles’ big eyes enabled them to recognize enormous shapes, which would constitute food.


Ichthyosaurs were carnivorous, and given their vast variation in size and extended lifespan, it is likely that they consumed a variety of animals. The ability to snag smaller creatures was developed in species with pointy mouthparts, which is a notable feature of Ichthyosaurs. Skeletal remains in fossilized stomachs point to larger prey species, such as sea turtles and birds, as well as fragments of prey that range from cephalopods, and all kinds of fish.


The classification of Ichthyosaurs as amphibious resulted from the discovery of new skeletal remains, occasionally with corresponding connective tissues. The sculptures’ location on the shores of islands amid artificial lakes further supported the idea that Ichthyosaurs lived in an amphibious environment. 

Large Ichthyosaurs specimen fossilized
Large Ichthyosaurs specimen fossilized

The existence of Ichthyosaurs in polar regions can be attributed to the fact that they were warm-blooded animals with shielding excess fat that would keep them warm during greater-depth swims into extremely cold mesopelagic zones in search of prey as well as help them tolerate journeys into chilly waters at northern latitudes.


Ichthyosaurs were viviparous, which means they gave birth to live children rather than eggs. Despite the fact that they were reptiles and evolved from external fertilization forebears, viviparity is not as unusual at first glance. Air-breathing marine animals must either give birth to live offspring in open seas, such as dolphins and whales, or hit the coast to produce eggs, as tortoises as well as some sea serpents. 

It would have been difficult, if not impossible, for Ichthyosaurs to get far enough on land to lay eggs considering their sleek and diagonally flat bodies, which were extensively specialized for quick swimming. If compared to placental mammals, ichthyosaur fetuses are frequently quite small and numerous in each batch.


Natural predators of Ichthyosaurs were other members of its species and sharks; however, this wasn’t the reason for their extinction. Recent research suggests that the Ichthyosaurs’ extinction happened in 2 stages. Feeding groups were exterminated by the first extinction event at the start of the Cenomanian ages. During the Cenomanian-Turonian border event, the second major Ichthyosaur extinction occurred, and just one species remained.

Fossil of an Ichthyosaurs found in England
Fossil of an Ichthyosaur found in England

Thus, rather than a gradual decrease, the Ichthyosaur extinction unfolded in a couple of rapid occurrences. These events were likely triggered by the climatic and environmental shifts that occurred in the Cenomanian and Turonian ages.

Facts about the Ichthyosaur

  • Ichthyosaurs were viviparous species.
  • Ichthyosaurs had about 150 teeth.
  • Ichthyosaurs weren’t technically dinosaurs but marine vertebrates.
  • Ichthyosaurs lived anywhere between 90-250 million years ago.
  • Ichthyosaurs had the biggest eyes of any animal spanning 10 inches across.


How fast can an Ichthyosaur swim?

According to estimates, ichthyosaurs could swim up to 25 mph. They were air-breathing and viviparous, just as contemporary cetaceans like dolphins and whales are, as some adult fossils have even been found with fetuses inside.

Why are Ichthyosaurs not dinosaurs?

Ichthyosaurs are a different phylum of aquatic vertebrates that were not dinosaurs. Researchers really do not know which species of vertebrates were comparable to ichthyosaurs because they were so evolved and altered for the oceanic environment.

Why did Ichthyosaurs have big eyes?

Compared to extant marine mammals and reptiles, many species of prehistoric aquatic Ichthyosaurs possessed eyes that were considerably larger, given their body proportions. Recently, it has been proposed that the cause for these species’ big eyes is their responsiveness to low light at extreme depths in the deep-diving genus Ophthalmosaurus.

Was an Ichthyosaur bigger than a blue whale?

According to researchers, the ichthyosaur, which lived 200 million years ago, was bigger than a blue whale. At a staggering elevation in the mountains of Switzerland, they were excavated from rocks. The Shastasaurus sikanniensis, a whale-like dinosaur that may have reached a length of 70 ft, is the longest Ichthyosaur known to science.

How many eggs did Ichthyosaurs lay at a time?

Although one specimen of an ichthyosaur reveals 11 embryos maintained within the body cavity, the majority of Ichthyosaurs would give birth to 1 or 2 single newborns, commonly known as pups.

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