The study of fossil materials is very important in the geological and biological researches. They can involve ancient past,
evolution or extinction of species, oil prospecting and the understanding of different areas such as: paleoclimate, paleoecology,
paleogeography, in addition of climate, environmental changes and life. Araripe Geopark is located in the south area of the
Ceará state in the Northeast of Brazil and it provides a general overview of the Earth’s History. In this study the vertebral
column extinct fish, Cladocyclus ferox and its nodule from Santana Formation, Northeast of Brazil, calcite and apatite minerals, and vertebral column of recent
fish, Opisthonema oglinum were investigated by means of thermal analysis. TG/DTG and DTA curves showed decomposition processes, suggesting water evolution,
calcium carbonate and phosphate decomposition and thermal transitions indicated that fossilization processes of fish, carbonaceous
material involved the fossil after its death and the organic substance was replaced by inorganic compounds.