The Seas of the Mesozoic from the Dinosaur Collector

The Middle and Late Jurassic Sea

At the end of Early Jurasic plesiosaurs and ichthyosaurs are winowed. Pliosaurs get really big There were two major groups.   New marine crocodiles and the first sea turtles are present appear. Middle Jurassic primitive turtle Eileanchelys waldmani. The turtles were found alongside fossils of other aquatic species such as sharks and salamanders that would have lived in a landscape made up of low-salinity lagoons and freshwater floodplain lakes and pools.

Updated 8/12/2011

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Modern crocs use their tails not their limbs to swim. Metriorhynchus legs look like flimsy flippers in most reconstructions. This maybe a product of the deformation after fossilization. There are fossil finds that indicate a flat functional foot. There is no evidence at all that Metriorhynchus laid its eggs anywhere but on land so a more functional foot would have been useful.

UHA Kaiyodo Metriorhynchus.

Ophthalmosaurs appear in the Middle Jurassic and they diversify to fill the slots with the extinction of many of Early Jurassic icthyosaur famililes. Ophthalmosaurs are found world wide. The final ichthyosaurs are in first of the Late Cretaceous. Ophthalmosaurus (Eye Lizard)  was about 15 feet long.  Its almost toothless jaw was adapted for catching squid and fish. It had the largest eyes of any Vertebrate fossil.  This indicates that it hunted in the dark depths of the oceans. The body is stream line for speed but they may not have been warm blooded. This would have limited endurance.

Toyway Ophthalmosaurus   from Walking with Dinosaurs.

Pliosaurs get bigger. They fill the killer whale and Sperm whale niches becoming the top predators at sea. Pliosaurus the namesake for the family lived Kimmeridgian of England.

Invicta Pliosaur and PlayVison Metriorhynchus.

Plesiosaurs die out at the end of the Jurassic. The long necked elasmosaurs of the Cretaceous evolved from a short necked ancestor.

Invicta Pliosaurus and Plesiosaurus by Fred Snyder

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