Genesis 1 tells us that God filled the waters with all kinds of snapping, flopping, swishing life. You may think of animals like whales and sharks and lobsters, and those kinds were there. But God also made some amazing reptiles to slip through the waves.
Many of these marine reptiles (that’s a fancy way to say reptiles that live in ocean water) were huge. How big? About the length of a train car.
Also, because these creatures were reptiles, they didn’t have gills and couldn’t breathe underwater. Like whales or turtles or seals today, they had to come to the surface to gulp in air.