Dinosaur biostratigraphy studies the distribution of dinosaur taxa through rock layers. It can be useful for dating and correlating rock units and reconstructiong ancient ecosystems. Most dinosaur-bearing rock formations do not contain multiple distinct stratigraphically separated faunas. Typically dinosaur faunas are static throughout a formation or change piecemeal over time. Faunal turnover usually occurs between formations. The fossil record can give an appearance of faunal turnover due to multiple causes including evolution, migration, or changing . Turnover events can have extremely minor causes like the migration of a taxon to a new area or extremely conspicuous ones like an ecosystem destroying catastrophe. Since the fossil record is incomplete assessing the nature and causes of fa