Sunday, 11 January 2015

Walking with whales

University of California Press Oakland CA 2014
ISBN 978-0-520-27706-9
This highly readable book by Hans Thewissen recounts a scientific odyssey in search of the ancestors of whales. Almost all the relevant fossils were found in Pakistan and western India. Dr. Thewissen worked there under trying conditions and in the shadow of political conflicts (his first field expedition was foreshortened by the 1991 Gulf War). He succeeded, however, in uncovering an evolutionary series of walking whales and eventually in demonstrating their affinity to even-toed ungulates (Artiodactyla).

The key discovery (here), made independently by Gingerich (here), was that ancestral whales possessed the double pulley astragalus (ankle bone) that is a defining feature of artiodactyls. The author does a very good job of explaining this and other anatomical details. Indeed, this book was written for the general reader and its author is at pains to explain the necessary terminology. He also gives fascinating insights into several aspects of cetacean biology such as the way in which aquatic mammals, including fossil and living whales, propel themselves through the water. 

The relation of whales to artiodactyls, with hippopotami as the closest living relatives, was first proposed on the basis of molecular phylogenetics (e.g. here). Because there is no fossil record for hippopotami, Dr. Thewissen does not find this analysis very useful. He prefers to keep Cetacea as a separate order even though this makes Artiodactyla paraphyletic.

Of particular interest to me are Dr. Thewissen's studies of a series of dolphin embryos and his proposed research on embryos of the bowhead whale.

This is a deeply personal book and no attempt is made to hide the author's prejudices. He is so concerned about Japanese whaling that he missed an opportunity to collaborate with Seiji Ohsumi, the grand old man of cetacean research who has done seminal work in reproductive biology.

Ohsumi S: Comparison of maturity and accumulation rate of corpora albicantia between the left and right ovaries in cetacea. Sci Rep Whales Res Inst 1964; 18:123-148. 

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