Complex sentence: Some marine reptiles, such as ichthyosaurs and mosasaurs, rarely if ever ventured onto land and gave birth in the water, while others, such as sea turtles and saltwater crocodiles, still return to shore to lay their eggs.
Split into simpler sentences: Some marine reptiles, such as ichthyosaurs and mosasaurs, rarely if ever ventured onto land and gave birth in the water. Others, such as sea turtles and saltwater crocodiles, still return to shore to lay their eggs.