While faux fossils may be the bane of collectors, from a prop standpoint the linked article is a treasure trove of information for anyone looking to create their own fakes. Some of the techniques are obvious, such as carving the skeleton in relief and then staining it, but others are surprisingly inventive.
"The techniques utilized in creating PTEROSAUR and BIRD FOSSILS are identical and equally apply to both fossil types. Predominantly, these two methods are employed together:
1. Carving, sculpting, painting portions of the fossil that never were there INCLUDING SOFT TISSUE AND FEATHER IMPRESSIONS!!!
2. Assembling several components of fossil bones from several different incomplete animals into one animal.
3. Utilizing modern bird (or other type) bones arranged and embedded on a matrix slab or artificial matrix rock."