Chapter 1: Finding Your Inner Fish

Chapter 1  –   Finding Your Inner Fish

1. Explain why the author and his colleagues chose to focus on 375 million year old rocks in their search for fossils.  Be sure to include the types of rocks and their location during their paleontology work in 2004.

The author and his colleagues chose to focus on 375 million year old rocks in their search for fossils because amphibians that look dissimilar to fish were discovered in 365 million year old rocks, while fish without amphibian characteristics were discovered in 385 million year old rocks. Thus, it is possible that the evolutionary intermediary, or the “missing link” between fish and amphibians, would be discovered in 375 million year old rocks, between the two time periods. The rocks examined were sedimentary in composition, as the gradual and relatively gentle formation of sedimentary rock under conditions of mild pressure and low heat are conducive to the fossilization of animal remains. Sedimentary rock is also often formed in rivers and seas, where animals are likely to live. This site provides a resource that describes means by which fossils are formed and how the fossil record may be interpreted, and shows some examples of fossils demonstrating evolution through geological periods: In 2004, Shubin and his colleagues were looking for fossils on Ellesmere Island, in northern Canada. This location was chosen because of its lack of human development, as well as of obstructing natural formations and life forms such as trees, which signified that rocks of the correct age might be well exposed in that area.
2. Describe the fossil Tiktaalik.  Why does this fossil confirm a major prediction of paleontology?
The fossil of Tiktaalik confirmed a major prediction of paleontology in that it showed characteristics of both aquatic animals, such as fish, and land animals, such as reptiles and amphibians. While it had fins and scales, it also had a flexible neck, a flat head, and complex bone structure in its fins that correspond with the structure of the legs of terrestrial animals. Thus, it demonstrates the evolutionary transition between aquatic and terrestrial life. In addition, the missing link was found in the contextually correct time and place, preserved in 375 million year old rock, as was hypothesized, in the bed of an ancient freshwater stream. More information and several pictures of both the Tiktaalik fossil and a drawn rendering of Tiktaalik can be found here:
3. Explain why Neil Shubin thinks Tiktaalik says something about our own bodies? (in other words – why the Inner Fish title for the book?)
Neil Shubin bases his argument that the anatomy of Tiktaalik is relevant to that of humans by discussing specific features of the anatomy of Tiktaalik that vary from typical fish anatomy and correspond to features of the human body. For example, he points out that Tiktaalik has a neck that is able to bend independently of the rest of the body, unlike fish, and like all terrestrial vertebrates, including humans. The fin bones of Tiktaalik are also structures homologous to the human arm. Therefore, the evolutionary history of humans can be traced to an organism similar to Tiktaalik, as certain features of the anatomy of both correspond, which draws attention to the inherent commonality between humans and fish, resulting in the concept of the “inner fish.” A key concept expounded by this particular theory of evolution of terrestrial vertebrates is that of Shubin’s biological “law of everything,” which states that all organisms have parents, and thus that all of them are genetically descended from a parental source of genetic material. This is a central idea of chapter 11 (
This law is significant because it provides a rationale for the evolution and descent of all organisms, from Tiktaalik, a more sophisticated vertebrate descended from the freshwater fish of the North American continent, to humans, organisms with radically modified, but nevertheless homologous, anatomical structures.
Leave a comment


  1. Thanks Arman. As others add their entries you can link to related content in their posts. For example, the idea of homology will not doubt be mentioned again, as well as the significance of the skeletal structures. You can also find related links on the web.

  2. It’s interesting that scientists can distinguish between rocks that are only tens of millions of years old. After all, that is not much in the history of the earth. It’s also interesting that Tiktaalik displays homology to humans today, since it is hundreds of millions of years old.

  3. Morgan Moroi

     /  May 7, 2012

    I find the Tiktaalik fossil very interesting because it shows that transitional fossils do exist. This relates to the Bozo example in Chapter 11. The Bozo family members in the middle of the evolutionary tree serve as transitions from humans to clowns (just as Tiktaalik shows the transition from fish to amphibian). This fossil also shows how one random mutation can create an entirely new and functioning species.


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