Chapter two gives a summary of the history of mammal fossils. When first found in rocks dating back to the age is the dinosaurs, mammal fossils were considered primitive and identified as belonging to marsupials. This is a misconception due to the idea of animals changing to become more sophisticated (and human) over time. It is only in modern times that modern marsupials are shown to be just as sophisticated as placental mammals and evolved alongside, not from, the reptiles and dinosaurs.