The fossil is made of melted white chocolate chips: melt a cup of them in the microwave (1 minute, stir) or over a double boiler, then put in a zip-top freezer-safe bag with a small corner snipped off (start with 1/8" hole and see if it it's big enough), or use a pastry bag and a #3 or #5 tip. Trace onto waxed paper with an outline below, let it set up, then transfer to your dessert. Good surfaces include chocolate frosting, unfrosted brownies or chocolate cake, a frosted cake coated with graham cracker or cookie crumbs, or anything else that resembles rock or dirt.
You can make all kinds of designs this way- when I turned my kids loose, they made a pony (complete with chocolate jimmies on the mane and tale), a butterfly, a banana (covered in yellow sugar crystals), and a set of exploding fireworks.
At any rate, here's the recipe for the brownies, which were very moist and fudgy, with a crunchy, sweet topping:
Cookies and Cream Brownies
1 batch of your favorite brownie batter to fit a 9x13 pan (I used a Duncan Hines mix)
1 cup of vanilla pudding
8 oz. chocolate sandwich cookies, crushed
Mix the brownie batter according to its directions; bake as usual. When done, spread with the pudding, then sprinkle with the crushed cookies. Press the crumbs down lightly to make them stay. Best the first day; they get a little gooey by the second day.
If you're adding a 'fossil', wait until the brownies are completely cool.