Fossils 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.

The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa (phylogeny) are some of the most important functions of the science of paleontology. Such a preserved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 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.

The observations that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.

The image on the left shows the fossil remains of three Amonites, each measuring about 1.5cm across. The image on the right shows an Amonite as it looked it its natural state.

People have been finding dinosaur fossils for hundreds of years, probably even thousands of years. There are references to "dragon" bones found in Wucheng, Sichuan, China over 2,000 years ago; these were probably dinosaur fossils. Much later, in 1676, a huge thigh bone (femur) was found in England by Reverend Plot. It was thought that the bone belonged to a "giant," but was probably from a dinosaur. A report of this find was published by R. Brookes in 1763.

The first dinosaur to be described scientifically was Megalosaurus in 1824, by William Buckland. Buckland (1784-1856) was a British fossil hunter and clergyman who discovered some Megalosaurus fossils in 1819 and named the reptile in 1824. It was the first dinosaur ever described scientifically and first theropod dinosaur discovered (this is all in hindsight, because the dinosaurs had not yet been recognized as a separate taxonomic group - the word dinosaur hadn't even been invented yet).

Dinosaur fossils, as with other fossils, are found throughout earth's sedimentary layers. To date, approximately 95.0% of all earth's fossil remains are marine invertebrates, 4.74% are plants, 0.25% are land invertebrates (including insects), and 0.0125% are vertebrates. Of the vertebrates, the majority are fish. Moreover, 95% of all land vertebrates found consist of less than one bone. However, billions of fossils have been found. Up to as many as 1,200 dinosaur skeletons have been discovered thus far. Sedimentary rock (sandstone, siltstone, shale, limestone, etc) is primarily laid down by moving water, layer upon layer, in a process known as hydrologic sorting. Animals whose fossil remains are found must have been caught in this running water to have been buried and preserved. The remains would be sorted by density just as the rocks were. If not buried, the carcass would rot or be scavenged. Fossil remains of clams (found in the closed position, indicating they were buried alive) have been found atop Mt. Everest. Sedimentary layers and fossil remains seem to be a testimony to a past marine cataclysm. There are nearly 300 surviving Flood Legends passed down by ancient civilizations. Some suggest Noah's Flood.