Ichthyosaurs were reptiles that were strong swimmers fully adapted to life in the seas. They were better adapted than any other reptiles, although they still needed to go to the surface periodically to breathe air.

ANATOMY
Ichthyosaurs were stream-lined marine reptiles that ranged in size from 7-30 feet long (4.5-9 m). They had sharp teeth in long jaws, and big eyes. They had four crescent-shaped fins, a stabilizing dorsal fin, and a fish-like tail with two lobes. They breathed air with lungs through nostrils which were close to the eyes near the top of the snout.

They gave birth to live young; fossils have been found with baby Ichthyosaurs in the abdomen.

WHEN ICHTHYOSAURS LIVED
Ichthyosaurs lived during the Mesozoic Era, the Age of Reptiles. They appeared during the Triassic, reached their peak during the Jurassic, and disappeared during the Cretaceous, about 95 million years ago, millions of years before the K-T extinction at 65 mya (and before the extinction of the dinosaurs).

BEHAVIOR
Ichthyosaurs lived in the oceans, probably near the surface (they had large eyes, which would be unnecessary is they spent a lot of time diving into the dark depths of the oceans. They did not move about on land.

REPRODUCTION
Ichthyosaurs were viviparous; they gave birth in the water to live young (instead of laying eggs, as other reptiles do). This is known because the fossilized bones of baby Ichthysaurs have been found inside the bones of adults.

DIET
Ichthyosaurs were carnivores; they ate fish, octopus, and other swimming animals. They had strong jaws and sharp teeth.

LOCOMOTION
Ichthyosaurs were fast and strong swimmers; they stabilized themselves in the water with their four, strong, crescent-shaped fins. Primitive Ichthyosaurs swam in a fish-like fashion, moving the tail from side to side to propel themselves through the water. Ichthyosaurs could not move about on land.

CLASSIFICATION
Ichthyosaurs are reptiles, but not dinosaurs. They are:

• Kingdom Animalia (animals)
• Phylum Chordata
• Subphylum Vertebrata (vertebrates)
• Superclass Tetrapods (four limbs)
• Class Reptilia (reptiles)
• Subclass Diapsids - these include all the reptiles (except turtles) and birds. They are distinguished by having two holes in the rear upper part of their skulls and two holes behind the eyes.
• Order Ichthyosauria or Ichthyopterygia - which includes 5 families of the marine-adapted reptiles:
  • Family Shastasauridae
    • Genus Cymbospondylus - 33 feet (10 m) long with one fin on the back and no fins on the tail, it had four paddle-shaped flippers - it had sharp teeth in long jaws- lived during the mid-Triassic period in what is now North and South America.
    • Genus Shonisaurus - about 49 feet (15 m) long and a huge body (whale-like) four fin-like flippers, a dorsal fin, a fish-like tail, and teeth only in the front of the jaws - lived during the late Triassic period in North America.
  • Family Mixosauridae
    • Genus Mixosaurus - 3.25 feet (1 m) long with no fins (on either the body or tail), it had four paddle-shaped flippers - lived during the mid-Triassic period in North and South America.
  • Family Ichthyosauridae
    • Genus Ophthalmosaurus - 11.5 feet (3.5 m) long with a bulky body and huge eyes - the bone-lined eye sockets are 4 inches (10 cm) across - from the late Jurassic period in England, France, Argentina, and western North America.
    • Genus Ichthyosaurus - a dolphin-like reptile about 6 feet (1.8 m) long that could perhaps swim at 25 mph (40 kph). From England, Germany, Greenland, and Alberta, Canada during the early Jurassic to the early Cretaceous periods.
  • Family Stenopterigiidae
    • Genus Stenopterygius - 10 feet (3 m) long and dolphin-like, it had large eyes - from the early-mid Jurassic period in England and Germany.
    • Genus Platypterygius (meaning "flat wing") - 23 feet (7 m) long and dolphin-like, it had large eyes - from the early Cretaceous period in Queensland, Australia.
  • Family Leptopterygiidae
    • Genus Temnodontosaurus (aka Leptopterygius) - 30 feet (9 m) long with narrow flippers and a torpedo-shaped body - from the early Jurassic period in England and Germany.
    • Genus Eurhinosaurus - Unlike other Ichthyosaurs, it had an elongated upper jaw, perhaps used for obtaining food by poking into the sea bed. It was about 6.5 feet (2 m) long). From Germany during the early Jurassic period.