Esperanza. 2006 Dec 04. Ch. 8 & 9 of Zimmer. <http://development.pharyngula.org/ch_8_9_of_zimmer/>. Accessed 2008 Aug 20.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Monday, December 04, 2006

Ch. 8 & 9 of Zimmer

Chapter 8 of Zimmer involves the process by which whales went from walking to swimming. Frank Fish wanted to study how a warm-blooded mammal adapted its metabolism to water. He started by studying muskrats and videotaping them swimming in water. He discovered that with their mode of swimming they burned as much energy pound for pound and mile for mile as a human. He then went on to videotape many different mammals swimming. Fish’s theory of swimming development started with the dog paddle which is inefficient but enough for animals just crossing a creek and not living in the water. The next step would be the mode used by otters. The otter swims by pushing both hind limbs back together during a dive while bending its back so the undulation continues into its tail. This continues to push against water as the hind limbs move forward and would normally lose momentum. Fish declared that this was the way the earliest whales must have swum until their tails grew larger and more muscular and their backs became more flexible and loosed from their hips. Hans Thewissen found a skeleton of a whale that dated after Pakicetus but before Basilosaurus. It had forelegs that were short with great flat hands and hind legs that ended in feet shaped like clown shoes. It was a whale that walked and he named it Ambulocetus (walking whale). Not long after that Gingerich found a younger whale that had smaller legs than Ambulocetus that had normal functioning knees unlike Basilosaurus but the spine was no longer fused to the hips so that body resembled half a tail. He called this whale Rodhocetus.

Chapter nine deals with how to classify Archaeocetes, mysticetes, and odontocetes. At first scientists thought they descended from three different terrestrial vertebrates as archaeocetes did not have baleen teeth but theirs were differentiated dental work while more toothed whales have jaws full of identical pegs. A different whale, Aetiocetus, was discovered that resembled a baleen whale structurally in the skull except that it had teeth instead of baleen so it was decided that baleen whales descended from Archaeocetes.