Name means: Eye Reptile


Species: icenicus, natans

Range: Late Jurassic (Callovian-Tithonian, 166-146 MYA) from Wyoming, UK, Russia, Argentina, France, Mexico

Size estimate: 18-20 ft length, 1500-2000 lbs

Discovery: Harry Seeley, 1874

Classification: eureptilia, icthyosauria, neoicthyosauria, thunnosauria, ophthalmosauridae


It's no accident that Ophthalmosaurus looked like a dolphin. When unrelated animals live a similar lifestyle, they tend to share the same shape. Scientists call this phenomenon "convergent evolution." Like dolphins, Ophthalmosaurus and other icthyosaurs pursued swift-moving prey like fish and squid. Their streamlined bodies let them slip easily through the water. Dolphins and icthyosaurs shared other features as well. Both developed from air-breathing ancestors and needed to come to the water's surface to breathe. As a result, they both gave birth to live young. Pups would emerge tail first and swim immediately to the surface for a first breath. Some icthyosaur skeletons even show signs of experiencing decompression sickness, like modern whales. If they surfaced too quickly, gasses dissolved in their blood would decompress and form air bubbles. These bubbles could cause serious problems. Unlike whales, however, icthyosaurs moved their tails from side to side like fish.


Ophthalmosaurus may have preferred a diet of squid. Its snout had very few teeth. Eyes as large as 9 inches across let it see in dark waters or at night. It may have been able to stay submerged for 20 minutes. At even 2 mph an Ophthalmosaurus could dive as deep as 1900 feet and safely return to the surface within that time frame. Speed estimates for this animal range from 4 to 10 miles per hour. Comparisons of backbone design between the two species of Ophthalmosaurus show that icenicus could reach higher speeds, but natans was probably more agile.


Fossils of Ophthalmosaurus natans from Wyoming show that this animal lived in the Sundance Sea. This sea extended from the western ocean through Idaho and as far south as Salt Lake City. No remains of Opthalmosaurus have been found in Utah or Idaho, but they may have ventured into those areas.