Your Daily Fossil

Metriorhynchus

Reconstruction by Dmitry Bogdanov. 

When: Late Jurassic (167-155 million years ago)

Where: Europe

What: Metriorhynchus is an extinct marine crocodile-relative. It is a member of the most aquatically adapted group of crocodile-line archosaurs ever known, the Metriorhynchidae. Like the rest of this group, it was more streamlined than most crocs, having lost the heavy dermal armor (osteoderms) that characterize the vast majority of crocodylomorphs. Its tail was finned and its  feet were transformed into paddles, making it an excellent swimmer. Its snout was very narrow, which is correlated with eating fish in living crocodiles. The group Metriorhynchus  belongs to is the only clade in the crocodile lineage to have ever developed paddles, even though for much of the history of crocodiles they have been heavily linked with aquatic habitats. 

It is unknown how much Metriorhynchus and its relatives came onto land. As its feet are paddles, it is tempting to think that it never left the water. It would have assuredly been very slow and awkward on land, dragging its bulk with its relatively small paddles. However, there is no evidence of live birth in Metriorhynchus  or its relatives. In fact, no archosaur (dinosaurs + crocodiles) has ever been shown to assuredly have developed live birth. Thus, it is likely that Metriorhynchus did drag its 10 feet (~3 meter) long body out of the water to lay its eggs, much like the modern sea turtles.