Micropalaeontology is a branch of palaeontology that specializes in the study of microfossils. Microfossils are tiny palaeobionts or small parts of large palaeobionts, including many phyla such as ancient invertebrates (e.g., foraminifera, radiolaria and ostracoda) and ancient plants (e.g., diatoms and charophyta), some chitinozoans and conodonts that have not yet been properly classified, and small quantities of teeth of ancient vertebrates. Micropalaeontology is based on the size but not the types of the objects. For this discipline, it is crucial to develop proper techniques to extract or separate the tiny objects from the rock and to make thin sections for microscopic study. Because microfossils are tiny and abundant, they are usually used for stratigraphic correlations during exploration drilling.