Trilobite, any member of a group of extinct fossil arthropods easily recognized by their distinctive three-lobed, three-segmented form. Trilobites, exclusively marine animals, first appeared at the beginning of the Cambrian Period, about 542 million years ago, when they dominated the seas.

Sabre-toothed cat, also called sabre-toothed tiger, any of the extinct catlike carnivores belonging to either the extinct family Nimravidae or the subfamily Machairodontinae of the cat family ( Felidae). Named for the pair of elongated bladelike canine teeth in their upper jaw, they are often called sabre-toothed tigers or sabre-toothed lions, although the modern lion and tiger are true cats of the subfamily Felinae.

Dinosaurs, one of the most successful groups of animals (in terms of longevity) that have ever lived, evolved into many diverse sizes and shapes, with many equally diverse modes of living. The term "Dinosauria" was invented by Sir Richard Owen in 1842 to describe these "fearfully great reptiles," specifically Megalosaurus, Iguanodon, and Hylaeosaurus, the only three dinosaurs known at the time.

The semi-arid climate and cool temperatures deep within canyon caves have combined to create a perfect environment for preservation of more recent fossils. Pleistocene and Holocene remains have been unearthed within many of these caves, including 11,000 year old sloth bones, dung and hair, California condor bones and egg shell fragments, and pack rat middens.

This article appears in the June 2017 issue ofNational Geographic magazine. On the afternoon of March 21, 2011, a heavy-equipment operator named Shawn Funk was carving his way through the earth, unaware that he would soon meet a dragon.

Fossil, remnant, impression, or trace of an animal or plant of a past geologic age that has been preserved in Earth's crust. The complex of data recorded in fossils worldwide-known as the fossil record-is the primary source of information about the history of life on Earth.

The modern use of the word 'fossil' refers to the physical evidence of former life from a period of time prior to recorded human history. This prehistoric evidence includes the fossilised remains of living organisms, impressions and moulds of their physical form, and marks/traces created in the sediment by their activities.

Evolution is a theory, an idea with lots of evidence. It explains why animals and plants are so good at surviving in their environments, the places where they live. What it means is that a species changes over time and can even split in two new species.

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