Ichthyosaurs were:

Fish-like reptiles that evolved back into water around 200 mya.

The correct answer is Option (1) - Fish-like reptiles that evolved back into water around 200 mya.

 The amphibians evolved into reptiles. They lay thick- shelled eggs which do not dry up in sun unlike those of amphibians. Again we only see their modern day descendents, the turtles, tortoises and crocodiles. In the next 200 millions years or so, reptiles of different shapes and sizes dominated on earth. Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs). The land reptiles were, of course, the dinosaurs. The biggest of them, i.e., Tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth. About 65 mya, the dinosaurs suddenly disappeared from the earth.