Inner Fish Summary

Summary

Although, teeth are not the most popular bodily feature, they are very important to breaking down food and paleontologists. You can compare organisms with similar structures, like teeth, and see how closely related they are. The teeth of animals also reflect the diet they had and allows scientists to identify them as carnivores, herbivores, or omnivores. Teeth also make well preserved fossils because of their strong enamel. You can also learn a lot about an organism by understanding if their lower and upper teeth fit together and how often teeth are replaced. Scientists believe that the early teeth resembled that of reptile teeth, they did not fit together and were constantly changing and being replaced. Around 225 to 195 million years ago, teeth and the jaw started to change and develop to resemble a mammal.

The author of the book, Neil Shubin, went on a fossil expedition in Wyoming, Arizona, and Utah, with many other paleontologists also mentioned in the book, to study these early mammal fossils. One person that he went with was a man named Chuck, who actually taught the author a thing or two about finding fossils. During this expedition, Shubin learned that there are a few rules that paleontologists follow and how to spot fossils from the rock. With every fossil sites, paleontologists had to find a main area of exposed rock that contains the rock layer that they are looking for. However, even though Shubin can now spot fossils, finding the teeth of early mammals were very difficult because of their small size.

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Having to return to school, Shubin looked for other exposed rock to view/find other early mammal fossils. Shubin and many other paleologists went to Nova Scotia to look at exposed and eroded near the beach. He found a fossil here that is half mammal and half reptile. They also found limestone that contained the type of fossils they were looking for in and around volcanic rock. Within these fossils, they also found the first signs of teeth variation that many mammals, humans for example, poses.

Summary

Shubin had to study nerves for an anatomy final. A few nerves found within the human head also has many similarities to that of a shark. Humans posses twelve cranial nerves, nerves found within the head. They connect the brain to different body parts and organs and they can have odd paths within the body. Some nerves found within the head are called the trigeminal nerve, which allow us to chew, and the facial nerve, which allows use to have facial expressions. However, because of the skull, the human brain is hard to study. The skull is made of plates, rods, and a chuck of bone that holds up the brain. It also has a structure that not only contains a brain, but eyes and ear canals.

The human head is just a jumble of cells in the early stages of embryos. In about a month, four groups of cells called arches start to form. These arches develop into the tissues on the head. There is a set of Hox Genes located within each arch to tell it what to become. In humans, the first arch forms the jaw, the second arch forms the ear and parts of the face, the third and fourth form the throat. These arches have many similarities to that of sharks and other fish. The four arches work and develop much the same. For example, the first arch in both humans and sharks develop the jaw bones. This comparison was extended when Shubin looked at the arches of frogs, and a word called Amphioxus, which has a version of a backbone even though it is an invertebrate. These development of arches helps further the idea that we and many other organisms come from a similar ancestor.

Summary

Animals and humans have a similar body plan. We are both multi-celled organisms, about two trillion cells in the human body, and there usually is a head in the front of the organism. However, it may be harder to compare these organisms to some of the earlier organisms, like jellyfish, because the head may not be front and center.

One way you can compare these similar body plans is by looking at embryos. Shubin also studied embryos. He would look at a blastocyst, a cluster of cells that forms after conception, and how the cells would divide and expand to make tissues within the uterus. He was very fascinated by the way that chicken, fish, and amphibians developed similarly. Karl Ernst von Baer, a biologist, also noticed this and studied their embryotic process. He learned that the organs contained and developed from three germ (tissue) layers. The first germ layer is the ectoderm, which would become the skin and nervous system. The second was the mesoderm which becomes the muscles and skeleton. The third layer was called the endoderm and it will form the inner organs. Von Baer also realized that most vertebrates also have these three germ layers but form differently within the embryo. Knowing the similarities between the embryos of organisms, Von Baer predicted that the embryo goes through its evolutionary path within the womb.

A German scientist named Hans Spemann studied cells of embryos. His research concluded that the blastocyst has the ability to make a body. Another scientist called Hilde Mangold also tested this out by taking a chunk of a newt embryo and put it into the womb of another organism. The newt embryo was able to grow a body within the other organism. She then labeled the chuck of tissue the Organizer.

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