1. The missing link between amphibians and fish2. The Tiktaalik3 fossil. Evolutionary history4. Mammals5. Darwin's Theory 1.) The author and his colleagues chose to focus on rocks that were 375 million years old because they believed they contained the missing link between amphibians and fish. The rocks examined by the author and his colleagues were sedimentary rocks, which are often found in rivers and seas. 2.) The Tiktaalik fossil had fins and scales, as well as having a flexible neck, a flat head, and a complex bone structure. The discovery of Tiktaalik confirmed the evolutionary transition between aquatic and terrestrial life. 3.) The evolutionary history of humans corresponds to that of Tiktaalik, as we share many similarities, structures and characteristics of our anatomy. These commonalities between our genetic material underlie a chain of descent between fish and humans. 1.) The pattern discovered by Sir Richard Owen showed common bone placement among all mammals, as they all had the same connection order. This relates to his idea of ​​exceptional similarities as it relates to the idea that animal bones have a similar fundamental design. 2.) Charles Darwin's theory stated that organisms that share similarities share a common ancestor. 3.) Further examination of the Tiktaaliks fin leads to (Chapter 31.) During the 1950s and 1960s, Edgar Zwilling and John Saunders examined the effect that cutting and moving the tissues of chicken embryos would have on the development of the embroyo. . Zwilling and Saunders discovered two pieces of tissue that controlled limb development and tested the effects of its removal at different times during the life of the embryos. 2.) The Hedgehog gene controls the development of various appendages in all limbed organisms. In chickens, the hedgehog gene is found in the wing bud and controls the development of the little finger and thumb. Inn Humans, the gene is found in the arm of an embryo in the eighth week of embryonic development and controls the development of arms, wrists and hands. Chapter 41.) Teeth contain high amounts of hydroxyapatite within them, making them stronger and more likely to fossilize rather than decay. Conodonts are organisms with spikes protruding from their bodies, lampreys being an extinct species that contains them. 2.) Shubin states that the creation of teeth allowed for the creation of hair, feathers, and breasts since they are all developed from the ecdoderm.