The historic dinosaur period covers 170 million years, from about 235 million to 65 million years ago. Over this enormous time period, many species of dinosaurs evolved, and became extinct. The phenomenon is demonstrated by the fossil record. There have been five mass extinctions in the Earth's history. The environmental factors include climate change, changing sea levels, volcanism and cosmic events such as asteroid impacts or changes in the Earth's orbit.
Carbon is used because it is the backbone of all organic material.
Older samples have too little carbon-14 to provide an accurate measurement. These isotopes have much longer half-lives. For example, all human beings are a single species. There are thousands of species of dinosaurs. The species, or scientific, name is a two-part Latin designation.