Fossils（from Latin fossus,literally“having been dug up”）are the preserved remains or traces of animals,plants,and other organisms from the remote past.The totality of fossils,both discovered and undiscovered,and their placement in fossiliferous（fossil-containing） rock formations and sedimentary layers（strata） is known as the fossil record.Such a preserved specimen is called a“fossil”if it is older than some minimum age,most often the arbitrary date of 12,000 years ago.Hence,fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archaean Eon several billion years old（表9.1）.