The key to making a painting of a dinosaur look three-dimensional is to look at actual models. By setting up a variety of models in actual sunlight, you can see what happens with the textures and the reflected light.
This painting called "Chasing Shadows" shows a Brachiosaurus walking on a beach. He's lit from behind by a late morning sun, and the light is bouncing up from the warm sand onto his belly. Surrounding the painting are digital photos of a variety of dinosaur sculptures. The ones on the bottom are by Kaiyodo, a Japanese company. The ones in the upper right are by David Krentz, a very talented sculptor who has worked for all the movie companies. The little head just to the right of the figures is from Jurassic Park.
It's a good idea to work from the inspiration of a lot of different models, so you're not basing the painting on just one. Each model has unique little nuances. It also helps to paint the models a flat, neutral gray tone, so that they photograph well, and you can see the form more clearly.