If we will base it on the recent fossil which was recently found in Japan-- the Unique
Mosasaur fossil last December 8, 2015, ( this was found after the discovery of
the Dinosaur relatives and first dinosaurs (Dec. 7, 2015) by the University of
Utah), most possibly, these creatures existed during the Mesozoic
Era. During this period, Dinosaurs surround the planet for about 165 million years. In the Earth’s
history, this era is called the Mesozoic Era.