| Ophthalmosaurus (meaning “eye lizard” in
Greek) was an ichthyosaur of the Late Jurassic period (165 to 150
million years ago), named for its extremely large eyes. It had a
graceful 6 meter long dolphin-shaped body, and its almost toothless jaw
was apparently adapted for catching squid and fish. Major fossil finds
of this species have been recorded in Europe and Argentina.
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 front limbs were
more developed than the back ones, which suggested that the front fins
did the steering while the tail did the propelling. However,
Ophthalmosaurus' chief claim to fame is its eyes which were
extremely large in proportion to the 6 meter body, at 4 inches in
diameter, and suggest that it was probably a nocturnal hunter. The eyes
occupied almost all of the space in the skull and were protected by bony
plates (sclerotic rings), which most likely served to maintain the shape
of the eyeballs[1]
against water pressure at depth.
Calculations suggest that a typical
Ophthalmosaurus could stay submerged for approximately 20 minutes or
even more[2].
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.
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