Ophthalmosaurus was a jurassic ichthyosaur about 19.5 feet long. It fed on squid and other small marine life. It had a long toothless beak, which would have been ideal for squid and other soft bodied animals. Another interesting fact about this animal is that it gave birth to live young underwater. These baby Ophthalmosaurus would emerge tail first to prevent drowning. Ophthalmosaurus had thick bony plates surrounding it's extraordinarily large eyes. These plates are called sclerotic rings, and aid in supporting the eye.
Several of the sources I read stated that an Ophthalmosaurus would swim to a maximum depth of 600 meters. To me, this seemed a rather small number, so I decided to compare this depth with some modern day air breathing hydrophiles, the whales. I chose the species most similar in size to an Ophthalmosaurus, the Short-Finned Pilot Whale, or Globicephala macrorhynchus. These modern day sea giants can swim to a depth of 1000 meters, with nothing but a breath of air and some relatively strong bones. Using this information, I approximate that an Ophthalmosaurus could dive to a depth of around 1300 meters. Being a reptile, Ophthalmosaurus has a slower breathing rate than it's modern day equivalent, so it could spend more time swimming down. The enormous sclerotic rings of the Ophthalmosaurus also bring me to believe it could swim deeper than a pilot whale, as these rings could help keep the soft vulnerable eyes safe from pressure changes. Diving deeper would also account for the fact that the eyes were huge, these would be necessary in the low light. This depth would also place an Ophthalmosaurus in the top layers of the bathypelagic zone, home to more soft bodied organisms which Ophthalmosaurus' toothless beak could easily prey on. 1300 meters makes more sense because of the Ophthalmosaurus' body, and is not at all unreasonable looking at the depths of some air breathing underwater animals, such as the sperm whale, which can swim to depths of 3200 meters.
That about wraps up today's ancient organism. Next time it'll be a sauropod, I promise.
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