snowcat. 2006 Dec 17. Zimmer 5. <http://development.pharyngula.org/zimmer_5/>. Accessed 2008 Sep 07.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Sunday, December 17, 2006

Zimmer 5

Zimmer begins chapter five by asking how we can trace cetaceans’ ancestors back to land. The cetaceans are divided into two suborders: the mysticetes that have baleen and the odontocetes that have teeth. How dolphins swim has been studied by many scientists. They swim very efficiently and are propelled forward both on their upstroke and downstroke of the tail. Another interesting thing about dolphins is how they maintain their fertility. In theory dolphins should be overheating their gonads because of all the heat generated by swimming, but what actually happens is they reroute their circulation so that the gonads are actually cooled by swimming. It is thought that dolphins might swim by acting like a spring, but this has not been shown to be true conclusively. Blubber acts as evidence in support of the spring movement because it is shown to have a resilience value of 87%. A dolphin’s ability to echolocate is a very important innovation. Cranford wanted to study the anatomy of a dolphin involved in echolocation so he decided to make thin slices of the head and photograph the slices and scan the pictures into a computer which would then give him ability to visualize the structure in 3D. This method was not very useful or successful, but luckily he did a CT scan which turned out to be very useful. He found that the air is pumped by the larynx, through the nasal passage, and past the monkey lips which vibrate as the air passes through them. The air is not passed out through the blowhole though. It is brought back down into the nose so it can be used again. A dolphin’s ears are very different structurally from a land mammal’s ears. A dolphin’s ear is separated from its skull and is surrounded by pockets of foam and air. This prevents the dolphin from being confused about where sounds are originating from. The power of echolocation is amazing. Dolphins are able to tell if a ball is present from over 100 yards away, distinguish between different shapes of objects, and tell the difference between different types of metals. Dolphins are also able to understand commands from humans. If a trained dolphin is told RIGHT HOOP LEFT FRISBEE FETCH the dolphin will get the frisbee that is on its left and bring it to the hoop on its right. This suggests that the dolphins are able to understand abstract representations of things and their relationships to other things.