I am assuming you have limited resources from the geological department for taxonomical references. Since you are working with Miocene materials, most taxon are close related to extant species, you will start with local field guide of mammals:
on each species you need to find a local museum or university which has stored skeletons or specimen so you will give a visit, maybe more than a day or two, to make some notes and photographs of the bones.
Here are some article also to close to your area:
Article Late Miocene Mammals from Kocherinovo, Southwestern Bulgaria
Article Upper Miocene mammals from Strumyani, South-Western Bulgaria
Once you done readings you will have a good idea of what direction you should do next. I would definitely recommend you visit local museum for their collections.