One of the larger ichthyosaurs, Ophthalmosaurus was more
than 3rn/10ft long. (Some ichthyosaurs reached huge sizes,
in excess of 15rn/SOft in Iength.) The genus was named after
its remarkable distinguishing feature - its huge eyes. Each
eyeball was more than lOcrn/4in across and was housed in a
large orbit whose deepest recess almost touched that of the
orbit in the other side of the animal's skull. Around the orbit
was a ring arrangement of rectangular to wedge-shaped
bony plates, known as the sclerotic ring (see also below
right). All ichthyosaurs had this structure, which probably
protected the soft eyeball tissues from excessive water
pressure at depth. However, the ring was very large and
pronounced in Ophthalmosaurus.
Ichthyosaur details and lifestyle