Ichthyosaurs were large dolphin-like reptiles. They looked much like a fish but were really reptiles and often had to swim to the surface to breathe air.
The Australian ichthyosaur, Platypterygius, grew up to 7m in length and was one of the last- known ichthyosaurs. The entire group became extinct worldwide soon after the inland seas withdrew from Australia.
Ichthyosaurs had some of the largest eyes known from any creature in the animal kingdom. This would have given them excellent eyesight in low light – an advantage when diving to the darkest depths of the sea to hunt squid.
(Artwork by Maree Marwell)
Science has discovered a lot about the eyesight of ichthyosaurs because parts of ichthyosaur eyes are commonly preserved as fossils. Ichthyosaurs had plates of bones inside their eyes called the sclerotic ring. These give palaeontologists an indication of the size and shape of ichthyosaur eyeballs. The outer surface of the eye was nearly flat – much like that of a fish – and this helped to prevent light distortion when looking through the water.
The pointed snout of an ichthyosaur was similar in shape to that of a modern Bottlenose Dolphin or Freshwater Crocodile. These animals have narrow, tapering snouts that cut through the water in a scissor action to snap up small, agile prey. The strong snouts and cone-shaped teeth of Australian ichthyosaurs indicate that they had a generalised diet, including fish, squid, belemnites and ammonites
Most reptiles reproduce by laying eggs. Because their eggs cannot breathe in water, reptiles must make nests and lay their eggs on land. This is a problem for marine reptiles such as crocodiles and turtles, as they must leave the water and struggle up the beach to bury their eggs in sand.
Ichthyosaurs had found a way around this problem by giving birth to live young – miniature versions of adults that could immediately swim to the surface to breathe. Some remarkable fossils have been found in different parts of the world that record the process of ichthyosaur birth.
