Atmospheric conditions in the cretaceous period were very different than they are today. Research suggests that dinosaurs lived in a low oxygen world containing five times more carbon dioxide then in today's world. Spinosaurus was able to adapt in this time period with a low oxygen level mainly due to spending large amounts of time in the water. However, the spine lizard became too specialized of a creature to modify itself when the ecosystem went through massive changes. Rivers dried up and most of the Spinosaurus' food sources died with it making it difficult to find food or compete with larger
