Paleontologists study past life through analysis of the fossil record. Vertebrate paleontologists are particularly interested in studying those animals with vertebral columns (backbones). The biology of vertebrates is dictated by the millions of cells that make up these complex animals. Histology is the science concerned with the microscopic anatomy of cells, tissues and organs. All life forms are made of cells (membrane-bound bodies within which the chemical reactions necessary to sustain life occur). In complex animals, such as vertebrates, similar cells work together in associations called tissues. Typically, only the harder tissues of the vertebrate body become preserved as fossils. An example of a hard tissue is bone. Our ability to derive information from a fossil is dependent on how well it is preserved and on the techniques we use to study the specimen. Certain fossilization regimes conserve cellular and sub-cellular structure and microscopic examination of appropriately prepared specimens permits detailed study of fossil bone histology (Barreto and Albrecht 1993). The microscopic structure of bone reflects the activity of the cells that produced it. All organisms on earth, and all the cells that compose them are descended from a common ancestral cell; and we have no reason to believe that cells that produced bone millions of years ago were different from bone cells we can study in living animals today. It is possible to compare the cellular structure of well preserved fossil bone to modern bone. Such research, called “paleohistology,” allows interpretation of the biology of extinct vertebrates (Reid 1984; Ricqles 1976; Ricqles 1980).