The Walking Whales: From Land to Water in Eight Million Years, by J. G. M. ‘Hans’ Thewissen

Recently, astrobiologists (devoted to a discipline for which the evidence is yet to be discovered) have hypothesised about life on other planets such as Kepler 22-b, an aquatic world. “Swimming” through its liquid atmosphere, they imagine great whaleish aliens. Such images may be straight out of Doctor Who, but look back into our own deep time, and even more bizarre creatures once sported in the Earth’s ancient seas.

The origins of the primitive whales are utterly fascinating. These strange beasts, having only recently left the land, evoke an uncanny sense of chimeric creation. Are they hairy crocodiles, in the case of Ambulocetus, or the sea serpents of 19th-century imagination, like the gigantic Basilosaurus? Some seem fairly innocuous, such as the Kutchicetus, “the otter whale”. Others loom monstrously out of a horror tale, complete with jagged, compound teeth. They wouldn’t look out of place in the dinosaur park at Crystal Palace, as Victorian visions of a lost world.

Anatomist and neurobiologist J. G. M. Thewissen is well placed to reveal this remarkable aspect of mammalian evolution, and The Walking Whales is part biological text, part detective story. As geological chance would have it, most of our knowledge of the ancient whales – archaeocetes – comes from fossils in the decidedly unoceanic hills and plains of northwest India and Pakistan. In fact, these arid places once formed the Tethys Sea of the Eocene. What were once watery margins or open ocean now yield crucial evidence. And to gather it, the author braves possible kidnap, terrorist attack and the privations of desert living in the process of unearthing bony, three-dimensional jigsaw puzzles.

Most usefully for the biologically challenged, Thewissen often pauses from his dusty digging to deliver excellent lessons in whale anatomy. He points out, for instance, how the animals’ nostrils migrated over time from the tips of their snouts to the tops of their heads, allowing them to swim without bringing too much of their bodies out of the water to breathe. This evolutionary migration is itself a marker of the whale’s becoming; the slow movement from shallows-forager to deep-diver, and thus to modern cetaceans such as the sperm whale, which can dive a mile or more.

It is as if leaving behind the land has become the most extreme form of escape: plummeting into the ocean’s benthic zones, as far from terrestrial land as it is possible to get. The subtle development of their physiological equipment is fascinating. Thewissen dwells lovingly on the tiny tympanic ear bones for what these shell-like objects tell us about the leviathans from which they came. Their changing shape indicates how well an animal could hear in the water – and therefore how free from land it had become. “The ear makes the whale,” he concludes.

Thewissen is an entirely engaging and enthusiastic guide to this weird world. His adventures take on an Indiana Jones air as he digs out giant skulls from remote locations, and then tries to figure out how to get them back to the US. He is laughably underfunded – at one point he can’t afford the $1,000 (£640) it would cost to export an “awesome” skull that would vitally reorder our knowledge of “walking whales”. Later, he ends up in Japan – amid its contemporary minefield of captive and hunted cetaceans – to witness a living fossil: a dolphin born with hind limbs. For a moment, he is spun back into impossible prehistory, diving into deep time 48 million years ago when cetaceans reordered mammalian design, and with it, challenged our own earthly sway.