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Understand how decay and half life work to enable radiometric dating.
Dinosaur, the common name given to a group of reptiles, often very large, that first appeared roughly 245 million years ago (near the beginning of the Middle Triassic Epoch) and thrived worldwide for nearly 180 million years.
The extensive fossil record of genera and species is testimony that dinosaurs were diverse animals, with widely varying lifestyles and adaptations.
Their remains are found in sedimentary rock layers (strata) dating to the Late Triassic Epoch (approximately 237 million to 201.3 million years ago).
Soon thereafter, Lewis and Clark’s expedition encountered dinosaur fossils in the western United States. The bones described had been found in 1818 by Solomon Ellsworth, Jr., while he was digging a well at his homestead in Windsor, Connecticut.
At the time, the bones were thought to be human, but much later they were identified as .
Owen recognized that these reptiles were far different from other known reptiles of the present and the past for three reasons: they were large yet obviously terrestrial, unlike the aquatic ichthyosaurs and plesiosaurs that were already known; they had five vertebrae in their hips, whereas most known reptiles have only two; and, rather than holding their limbs sprawled out to the side in the manner of lizards, dinosaurs held their limbs under the body in columnar fashion, like elephants and other large mammals.
Originally applied to just a handful of incomplete specimens, the category Dinosauria now encompasses more than 800 generic names and at least 1,000 species, with new names being added to the roster every year as the result of scientific explorations around the world. A great many of them have been based on fragmentary or incomplete material that may actually have come from two or more different dinosaurs.
It became known as the , which he named from an incomplete skeleton composed of very large bones.
And if the artifact is organic—like wood or bone—researchers can turn to a method called radiocarbon dating.
In this interactive, learn how radiocarbon dating works, what it takes to determine a date in the lab, and why it's challenging to pinpoint a date precisely.
The tracks are now recognized as having been made by several different kinds of dinosaurs, and such tracks are still commonplace in the Connecticut River valley today.
Better known are the finds in southern England during the early 1820s by , a Newly Discovered Fossil Reptile, from the Sandstone of Tilgate Forest, in Sussex,” on the basis of several teeth and some leg bones.
Even earlier (1800), large birdlike footprints had been noticed on sandstone slabs in Massachusetts.