Complex sentence: Ichthyosaurs seemed to decrease in diversity even further with the Cretaceous-only three genera are known: "Caypullisaurus", "Maiaspondylus", and "Platypterygius", although they had a worldwide distribution.
Split into simpler sentences: Ichthyosaurs seemed to decrease in diversity even further with the Cretaceous. Only three genera are known, "Caypullisaurus", "Maiaspondylus", and "Platypterygius", although they had a worldwide distribution.