Written sources. Some examples of primary written sources are contemporary letters, eyewitness accounts, official documents, political declarations and decrees, administrative texts, and histories and biographies written in the period that is to be studied. Written sources help in cross-checking data or information collected from oral and other sources of historical knowledge. This help to reach reliable conclusions. Documents provide more detailed information than oral sources, e.g. dates, illustrative pictures, names of participants in events
Modern birds descended from a group of two-legged dinosaurs known as theropods, whose members include the towering Tyrannosaurus rex and the smaller velociraptors.
