Why are There no Water Dinosaurs?

Dinosaurs had conquered the world. No animal was and still isn’t larger than them. They had the skies and land. Then why not the water? Half as dominant groups such as mammals have token the seas. So why not the best rulers?

There are some dinosaurs that became semi-aquatic but no dinosaurs became fully aquatic. The most famous case of this is not an individual species, but rather a family- Spinosauridae. A group of carnivorous “crocs with legs” which had a strange affinity with water. This semi-aquatic adaptation wasn’t restricted to carnivores however. Another strange case is an ankylosaur named Liaoningosaurus paradoxus. This one though, isn’t confirmed yet but we do still have reasons to believe it was semi-aquatic.

The oceans and sea were already in habited by plesiosaurs and pliosaurs. These were the rulers of the water. Many people think that these were dinosaurs. That is not true. They are close relatives of the clade dinosauria. Many large and famous pliosaurs included kronosaurus and close clades like mosasauridae included mosasaurus and tylosaurus.

Dinosaurs were oviparous like 97% of all fish making people think they were perfect candidates but one key difference is the shell. The egg shells of fish were jslim like making them better underwater. Dinosaurs had eggs with harder shells. This made them worse for being underwater. Additionally, the pores would become water logged and the baby inside would suffocate proving fatal. 

Even if they lay eggs with shells like those of many fish and sea snakes there’s one major problem.

The bones of dinosaurs were lighter than other animals like mammals even if they both are the same size, and there is a reason for that. Dinosaurs had bones which has air pockets. These air pockets would make them lighter letting them be larger than any animal to ever walk on land. 

This might sound nice at first- becoming extremely large but this had a major flaw if they toke to the waters. Their lighter bones would make them buoyant which means they can’t deep dive. Dinosaurs like spinosaurus show that this change can happen, but from an evolutionary standpoint , might be completely impossible. And let us say that it could happen- there is still yet another problem they would have to overcome.

The limbs of dinosaurs (especially the feet) were getting further and further from the what was needed to go fully- aquatic. What was needed to become aquatic? To become aquatic, dinosaurs would need to stop evolving more pillar like feet and more weaker flippers. 

This change would be hard seeing that dinosaurs were evolving more pillar like feet. The way they were evolving their feet was better for bearing weight, but they would be terrible for water.

If dinosaurs didn’t die out in the Cretaceous-paleogene extinction event then maybe- just maybe- a dinosaurs, most likely from spinosauridae, would have token the seas and gave the dinosaurs a foot hold in the water. This is possible seeing that spinosaurus like the infamous spinosaurus do check a lot of the requirements. And breathing is simple compared to these problems.

Alas, dinosaurs died in the Cretaceous-paleogene extinction event. It would have been amazing to unearth a fully aquatic dinosaur. They likely would have had some fully aquatic dinosaurs. Dinosaurs truly are one of the most fascinating things in the world.