thumb|upright=1.3|[[Priscacara liops, fish fossil from Wyoming]]
Palaeozoology or paleozoology (Greek: παλαιόν, palaeon "old" and ζῷον, zoon "animal") is the branch of paleontology and evolutionary biology that specifically deal with the study of prehistoric organisms from the kingdom Animalia and the recovery and identification of their fossil remains from geological (or even archeological) contexts. The field also extends to the use of these fossil records for reconstructive phylogeny (via comparative anatomy and phylogenetics) and paleoecology, i.e. the study of ancient natural environments and ecosystems. Vertebrates are classified as a subphylum of Chordata, a phylum used to classify species adhering to a rod-shaped, flexible body type called a notochord.
In the early 1930s, paleontologists Chester Stock and Hildegarde Howard devised special units for quantitative paleozoology and quantitative paleontology. The first unit used, Number of Identified Species (NISP), specified exact quantity of fossils from a specific species recorded. Stock and Howard determined this unit to be problematic for quantitative purposes as an excess of a small fossil—such as teeth—could exaggerate quantity of the species. There was also an amount of confusion as to whether bone fragments should be assembled and counted as one bone or tallied individually.
R. Lee Lyman, Professor and Chair Department of Anthropology at the University of Missouri, writes that paleozoological research can provide data such as extinction rates and causes and "benchmark" peaks and drops in population which can be used to predict future patterns and to design maximally effective methods of controlling these patterns.