Fishing for clues: an artist’s idea of Pakicetus, the earliest whale (Image: NHM/SPL)

The intriguing story of how whale evolution was unpicked is told in The Walking Whales, revealing what it’s like to be a globe-trotting palaeontologist

WHALES evolved from cat-sized terrestrial hoofed mammals, evolutionary biologists tell us. How could a tiny, deer-like creature morph into such a radically different leviathan? The notion has often provoked gleeful ridicule from creationists, especially because, until the 1990s, so few intermediate fossils had been discovered.

Little more than a decade later, spectacular finds had bridged that gap so convincingly that whales now stand as one of the best-documented fossil transitions – literally a textbook case of evolution in action.


Much of that change is thanks to Hans Thewissen, a palaeontologist at Northeast Ohio Medical University in Rootstown, who has made many of the key discoveries. The Walking Whales is his account of his research.

Thewissen takes readers along step by step, beginning with his expedition to northern Pakistan in 1991 to find fossils of terrestrial mammals. When political tensions from the Gulf War cut short his fieldwork, he turned in desperation to one of the few specimens he had managed to bring home: a little bone that turns out to come from the ear of Pakicetus, a transitional species between land mammals and whales.

The find led Thewissen down a rabbit hole, changing the direction of his career. Chapter by chapter, he fills in the picture of fossil whales and their evolution, describing each of the major groups and showing how the bones give insights into their biology.

“A little bone from the ear of an ancient whale led Thewissen’s career in a whole new direction”

We see how limb bones adapted for walking become gradually more specialised for swimming, and how swimming styles shift from paddling to whole-body undulation to the even more efficient oscillation of a tail fluke.

We see eyes shift to the top of the head – the better to peep above the water, crocodile-style – and then move down to the sides as the proto-whales become more fully aquatic. Diets change from terrestrial plants to fish, and oxygen-isotope ratios of the teeth reveal the animals’ decreasing need to drink fresh water.

It is all rather complex and technical. Thewissen wants readers to really understand the details. Chapters frequently dive into arcane details of anatomy, complete with a fearsome thicket of terminology: osteosclerosis and pachyostosis, condyle and trochlea.

But, overall, the book does a splendid job of showing what it is like to be a palaeontologist. Thewissen’s vivid descriptions of fieldwork in Pakistan and India will give readers a clear sense of the joys and frustrations, and the tedium and excitement, that the work entails – right down to the rabid jackals and dry, gasoline-scented chapattis that are the price of working where the best fossils are found.

In keeping with this “you were there” approach, Thewissen doesn’t present the fossil whale groups in chronological order of their evolution, following instead the order of their discovery.

Consequently, he never explicitly lays out the whole evolutionary arc in an unbroken sweep. Instead, readers have to assemble the story themselves, although all the parts are certainly there to work with.

On the other hand, by focusing on the process of discovery, Thewissen gives us a rare sense of what it is like to be on the inside of a scientific revolution, as new finds suggest ideas, which, in turn, prompt the search for more data. For readers with more than a passing interest in the subject – and especially for any budding palaeontologists – Thewissen’s book is a perfect introduction to the field.

The Walking Whales: From land to water in eight million years J. G. M. “Hans” Thewissen University of California Press

This article appeared in print under the headline “The thrill of the chase”