You should set up a plane that matches the contour of the ground in the background plate. Don't worry about applying a material to it because you won't be using it. The default material will do just fine. Light the shot to cast the shadows you want then render the shadow on the plane as a seperate pass and composite in after effects.
If you're not familiar with rendering seperate passes then read up on it. The easiest set up would be to put the dino in a seperate render layer than the plane then batch render the dino as a beauty pass without the background or the plane under his feet then, render the plane BUT you only need to render the shadow pass so turn the other passes (beauty, diffuse, specular) off. Composite and make adjustment in after effects.
ps when you set up your lights, look at the shadows on the houses in the background. The dino shadows should match the direction. You can adjust the darkness and diffusion (blurriness) of the shadow in AE...
I rendered a dino onto a background using the techniques I just wrote about. You can see the clip here