I made a cake with dinosaurs hidden inside and let Eli excavate the first dinosaur. Step-by-step instructions on how to do this can be found at Instructables.
I reused the pull-string pinata I had made for Anja's Snow Bunny party. I just took the tissue paper off the outside, repainted the pinata, refilled it, and taped the trap door back on. This time it was completely torn apart, so there will be no more reusing it.
Another game I had planned was "excavate the dinosaur". The plan was for the kids to go digging in the snow in the backyard for dinosaurs, but it was -25 out. Instead I hid the dinosaurs in the living room and let the kids search for the dinosaurs indoors.
The last activity we did was make fossils from the dinosaurs they found on their hunt. (I forgot to get a picture of their finished products.) Idea found at Little Bit Funky.
I made fossil cookies for each guest to take home. The recipe and instructions can be found on Martha Stewart's blog.
...and here's a picture of our littlest one after she inhaled her cake