snowcat. 2006 Dec 04. Zimmer 8-9. <http://development.pharyngula.org/zimmer_8_9/>. Accessed 2008 Aug 30.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Monday, December 04, 2006

Zimmer 8-9

Chapter eight begins by talking about Frank Fish who studies how mammals swim. One of the big problems swimming mammals need to overcome is how to maintain their body temperature in water. Fish studied muskrats who overcome this problem is a similar way to dolphins. They manage their body temperature by changing to circulation of their blood, in warmer temperatures they dump heat by increasing circulation to the tail, in cooler temperature they shut down circulation to the tail to conserve heat. Then Fish became interested in developing a theory of how mammals swim. The least efficient technique, and the first one he suspects mammals used was the dog paddle. An improvement on the dog paddle is how otters swim. They do not alter their hind legs like in the dog paddle, but move them together; this resembles a terrestrial gallop in motor patterns. All that is needed for the whale to do at this point is grow a larger tail and have blubber in order to swim as efficiently as possible. Thewissen, who was a former student of Gingerich, was not very interested in whales, but ended discovering a whale that walked. This whale, Ambulocetus, resembled a crocodile and along with Gingerich’s Rodhocetus are important in understanding the origin of whales.

Chapter nine begins with discussion of how there were many species of whales that branched off in many directions. An important ancestral whale and one that could possibly have given rise to whales today is the Dorudon atrox. It had a long head attached to a flexible neck and a very long spine. It also had an important vertebra modification that allowed for the whale to generate more thrust per swimming stroke. Although this ancestor gets closer to our idea of a whale, it is still missing echolocation. Michel Milinkovitch used DNA sequencing to try to see how whales are related to each other. One issue he has to address with his version of the whale cladogram is that he suggests that baleen whales lost echolocation capabilities, which he explains by the fact that baleen whales didn’t need echolocation for feeding. Being a geneticist Milinkovitch is biased toward having more trust in a cladogram based on molecular biology than one based on morphology. Luckett, an anatomist and mammalogist believes that the molecular biologists need to think more like anatomists in order to build the best cladogram of the whale family. Zimmer concludes this chapter by talking about the encephalization quotient of various mammals and how it affects the IQ of different mammals.