• ✓About 12 m long, long robust head, powerful cone-shaped teeth, long heavy body
• ✓Four paddle-shaped flippers instead of legs, front pair larger than hind pair
• ✓Tail bends down into a crescent-shaped fin, like an upside-down shark tail
• ✓Small scales like a monitor lizard, dark above and pale below
• ✓Whole body in side view, swimming
• ✓Underwater in a shallow Late Cretaceous sea
• ✓Only this one species; no dinosaurs, text, people or modern objects

Checked by Claude Opus 5.5 (checked item by item from the image) on Nov 4, 2026. The score is the share of checklist items the image gets right; it is not an expert scientific review.

Prompt used to create the image

Scientifically accurate paleoart of Mosasaurus, a giant mosasaur (a marine lizard related to monitor lizards and snakes, not a dinosaur) from the latest Cretaceous (Maastrichtian, about 68 million years ago). Anatomy: about 12 m long, with a long, robust skull, powerful cone-shaped teeth and a long, heavy body; four paddle-shaped flippers instead of legs, the front pair larger than the hind pair; the tail bends down at the end into a crescent-shaped tail fin, like an upside-down shark tail (hypocercal fluke); skin of small keeled scales like a monitor lizard, dark above and pale below (countershading). Full body in side view, swimming underwater, whole animal visible, underwater in a warm, sunlit, shallow Late Cretaceous sea, a few small fish nearby for scale. Natural history museum illustration style, realistic textures and natural daylight, muted natural colors. Only this one species; no dinosaurs, no text, no labels, no humans, no boats, no modern objects.

Facts in the prompt come from Wikipedia (en) and Paleobiology Database