History of the Theory
In 1868, Thomas Huxley of England presented a theory that birds were descendants of a group of meat-eating theropod dinosaurs. His main evidence supporting this theory was the body type and skeletal resemblances shared between the two groups, and not seen elsewhere in the animal kingdom. These included the matching ankle joints, ilia, air sacs and hollow bones, a foot with a rear-facing fourth toe, and a similar build.
In America, Othniel Marsh had come to the same conclusions, and though evolution was not a widely accepted theory, his findings were generally accepted until the 1920s. At this time, Gerhard Heilmann wrote a book called The Origin of Birds in which he concluded that although they shared many characteristics, theropods lacked collarbones which are a defining feature of birds when fused to form the furcula or wishbone (this was later disproved). He argued that the bones could not be lost then re-evolved and deduced that both dinosaurs and birds evolved from a common pre-dinosaurian reptile. This became the common pattern of thought until the 1960s. In the late 1960s at Yale University, John Ostrom was examining the fossilized skeleton of Deinonychus and noted that it was bird-like in almost every way. He recorded twenty-two features in common, and this reset the thinking on the origins of birds. Since then many discoveries have been made to further suggest that birds did in fact evolve from dinosaurs. |