• ✓About 11 m long, long slender body, long head
• ✓Snout ends in a long, blunt, toothless bony tip well in front of the first teeth
• ✓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 the Late Cretaceous Western Interior Seaway
• ✓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 Tylosaurus, a large mosasaur (a marine lizard related to monitor lizards and snakes, not a dinosaur) from the Late Cretaceous (about 85 million years ago) of the Western Interior Seaway of North America. Anatomy: about 11 m long, with a long, slender body and a long skull; the snout ends in an elongated, blunt, toothless bony tip (rostrum) that sticks out well in front of the first teeth; 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 the warm, sunlit open sea of the Western Interior Seaway of North America, 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