M. Cuvier proposed a system called the Correlation Theory. The idea is that the way any body part works is usually the same. Toes work the same, no matter the critter they are attached to or when it lived. The more specific the details, the closer you are to figuring out the fossil or bone you have.

There are obvious problems, and the Naturalist has to keep checking and adjusting any conclusion. But it’s a good system.

Paintings of Dinosaurs usually show them with reptilian skin, in colors and patterns similar to today. The assumption is that camouflage is useful to both predator and prey, and doubtless was 160 million years ago too.