Before the Cambrian explosion, [b] most organisms were relatively simple, composed of individual cells, or small multicellular organisms, occasionally organized into colonies. As the rate of diversification subsequently accelerated, the variety of life became much more complex, and began to resemble that of today. The seemingly rapid appearance of fossils in the "Primordial Strata" was noted by William Buckland in the s,  and in his book On the Origin of Species , Charles Darwin discussed the then inexplicable lack of earlier fossils as one of the main difficulties for his theory of descent with slow modification through natural selection. Interpretation is difficult, owing to a limited supply of evidence, based mainly on an incomplete fossil record and chemical signatures remaining in Cambrian rocks. The first discovered Cambrian fossils were trilobites , described by Edward Lhuyd , the curator of Oxford Museum , in
Explain how a paleontologist might use relative dating techniques to determine the age of a fossil
Radiometric Dating and the Geological Time Scale
Three skeletons were discovered in northern Arizona in , and the two best preserved were collected in The most complete specimen became the holotype of a new species in the genus Megalosaurus , named M. Welles in Welles found a larger skeleton belonging to the same species in
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