The trilobites are a marine type of animal that has been one of the most successful animals in the earlier stages of the history of life on this planet. They have existed for roughly 270 million years, from approximately 521 million years ago until 252 million years ago. Their beginnings are traced back in the Early Cambrian period, and they went extinct in the great mass extinction at the end of the Permian period.
So, the trilobites are a very common fossil in the time frame from 521 million years ago until 252 million years ago, but they went extinct than, so they are missing from the fossil records onward from that time, thus we can say that they are not common throughout the entire fossil record.
