ophthalmosaurus

The eye lizard, Ophthalmosaurus (1874)

Phylum : Chordata
Class : Reptilia
Order : Ichthyosauria
Family : Ophthalmosauridae
Subfamily : Ophthalmosaurinae
Genus : Ophthalmosaurus
Species : O. icenicus, O. natans, O. saveljeviensis, O. yasykovi

  • Jurassic (165 - 145 Ma)
  • 6 m long and 2 000 kg (size)
  • Ocans worldwide (map)

Like other ichthyosaurs, Ophthalmosaurus gave birth to its pups tail-first to avoid drowning them. Skeletons of unhatched young have been found in over fifty females on fossil finds, and litter sizes ranged from two to eleven pups.

Ophthalmosaurus had a body shaped like a tear-drop and a caudal fin like a half-moon. Its forelimbs were more developed than the hind ones, which suggests that the front fins did the steering while the tail did the propelling. Ophthalmosaurus’ chief claim to fame is its eyes which, at 4 inches in diameter, were extremely large in proportion to its body. The eyes occupied almost all of the space in the skull and were protected by bony plates (sclerotic rings), which most likely assisted to maintain the shape of the eyeballs against water pressure at depth. The size of the eyes and the sclerotic rings suggests that Ophthalmosaurus hunted at a depth where there is not much light or that it may have hunted at night when a prey species was more active.

Calculations suggest that a typical Ophthalmosaurus could stay submerged for approximately 20 minutes or more . The swimming speed of Ophthalmosaurus has been estimated at 2.5 m/s or greater, but even assuming a conservative speed of 1 m/s, an Ophthalmosaurus would be able to dive to 600 meters and return to the surface within 20 minutes.

In the bone joints of Ophthalmosaurus skeletons traces of decompression sickness (the bends) have been found, possibly caused as a result of evasive tactics. Modern whales have been known to get the bends when ascending rapidly to escape predators.