snowcat. 2006 Dec 17. Zimmer 6-7. <http://development.pharyngula.org/zimmer_6_7/>. Accessed 2008 Sep 06.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Sunday, December 17, 2006

Zimmer 6-7

In chapter six Zimmer begins by Culvier’s work on mammal’s teeth and how they are important in identifying species of animals. When Harlan brought his Basilosaurus, which was thought to be a giant reptile, to London Owen concluded it was a giant mammal. He was able to make this assertion because the Basilosaurus had the same pattern of teeth seen in marine mammals. Koch on the other hand was an example of scientists losing sight of what is important. He put together a fossil from five different animals called it a sea serpent and named it the Missourium. Fortunately true scientists did discredit him. Although Flower was just speculating, he was able to correctly guess the origin of whales. He said he believed that their ancestors were conventional land mammals and they were not a close relative to seals. Synapsids which were the earliest amniotes to become successful on land became that way largely because they evolved a new way to eat. They changed their jaws, muscles, and teeth so they would be able to slice food it the front of their mouth and chew it in the back. They also gained the ability to chew and breathe at the same time by evolving a nasal passage at the back of the mouth.

He begins talking about Gingerich in chapter seven, a paleontologist who never suspected he would be studying whales. Gingerich had an interest in land mammals and only ended up studying whales because he found Pakicetus, an early whale too extraordinary to ignore. From that time on Gingerich became obsessed with whales. When working on a Basilosaurus fossil Gingerich discovered legs. When a leg was found on a Canadian whale the leg is known as an atavism. Atavisms used to be discarded as freaks of nature by biologists, but it is now known that they are a mechanism by which evolution can occur. They can also be a step back into the past lineage of an organism. Another interesting idea is how tetrapods lose their legs. It might seem like they no longer use their legs and the legs waste away to nothing, this is not the case though. In order to lose their legs they must first elongate their bodies all the while stretching out and changing their organs, and then evolve a way of moving like a snake. It is also a fallacy to believe that an animal gives up a structure just because they have become useless. A fish could not go blind without gaining a new sensory organ, in this case lateral lines.