All of the fossils could be from fish,dinosoures,leaves, or plants. The reason why this could happen is because it could have happened thousand of years ago and the sea level could have been lower.
A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.