Dinosaurs come from the evolution of early primitive organisms approximately 230 million years ago and it is unknown why these organisms evolved into dinosaurs. Scientists have been able to trace dinosaurs back 228 million years ago to one of the first species known as the "eoraptor" that was the size of a dog and was carnivorous.
Although dinosaurs are now extinct, there are many living examples of the dinosaur through its descendants in the bird kingdom. Alligators and other reptiles are also descendants of dinosaurs, but they are later descendants and evolved from other animals that evolved from dinosaurs. It is believed that birds evolved from dinosaurs directly. There are many similarities between dinosaurs and birds including hollow bones, walking upright and closely related skulls.
When the dinosaurs were alive, people were not yet living. Humans came into existence approximately 2.5 million years ago, which is approximately 127.5 million years after the dinosaurs first evolved and 62.5 million years after the dinosaurs disappeared. Scientists base their findings about dinosaurs on the fossils they left behind and on the study of their closet relatives including the birds and reptiles living in the modern world. Through these studies, scientists have concluded that most dinosaurs laid eggs, provided parental care for their young and protected their eggs once they had been laid.