When I started this book, I was delighted with the opening narrative, which describes the author, Anthony Martin, accompanied by his students, searching out alligators in their burrows. Martin provides a fairly full picture of how alligators use their burrows, not only to escape dry, hot days, but also to rear young and maintain a watery refuge. Scanning through the chapter titles and image inserts, it was clear I would be reading the tales of many burrowing animals, extant and extinct, from arthropods to megafauna. After reading about human cultures that lived (or still live) underground, I skipped through the chapters, stopping to delve into those that piqued my interest. In the chapter on terraforming a planet, Martin describes his own doctoral research on trilobites in coastal Georgia, including details that provide insight into how we construct the past with the evidence at hand. This section alone would intrigue my students and allow them to see how science is done, as well as how professors interact with graduate students.
Moving on to the chapter “Playing Hide and Seek for Keeps,” I read with interest about trace fossils and body fossils of the Ediacaran. It was at this point that I realized the deeper story here: the narrative of how the evolution of complex life depended, and still turns, upon the knack of animals that burrow. Martin paints a vivid picture of the pre-animal world, and the effect of “mobile, grazing animals” upon that world, composed almost entirely of biomats:
Think of the biomats as barriers to animal progress … the first mobile animals had no claws, teeth, or other anatomical attributes to cut through them. Try to open shrink-wrapped CD cases … but without scissors, fingernails, or teeth, and you will quickly identify with Ediacaran animals. These films also effectively sealed underlying sediments from oxygen introduced by overlying seawater. As a result, oxygen-deprived sediments below biomats constituted hostile territory for animals. (pp. 195–196)
Martin goes on to describe in detail how the burrowing of animals not only disturbs the biomats, but also fundamentally alters what had been pristine anoxic sediments beneath them. In effect, burrowing animals began to transform the sea bottom while simultaneously positioning the animals for the burst of adaptive radiation we call the Cambrian explosion.
Every chapter takes a different slant, told with disarming personal information and entertaining turns of phrase that effortlessly pull in contemporary references, even Disney movies: “For a long time, the Earth was frozen – but let it go” (p. 197). From how burrowing mammals survived the asteroid 66 million years ago to how pocket gophers recovered from the eruption of Mount St. Helens, the big picture is rendered more real by the inclusion of vivid details and clear rationales:
This evidence for burrowing synapsids and their mammaliaform descendants before and after the Triassic extinction shows not only how these animals would have lived through major ecological calamities, but also how they avoided direct competition with dinosaurs on the surface. Does your world have predators with nasty, big, pointed teeth? Then go underground. Does your world also have animals large enough that, when they step on you, instantly turn you into a furry crepe? Then go underground. … Are forest fires, volcanic eruptions, … or other disasters making life a little more difficult? Then, well, you get it. (pp. 275–276)
The details of animal history, biology, related geology, and techniques of studying burrows all add up to a satisfying journey through the worlds of burrowing animals. Martin ends with an examination of the Anthropocene and how studying ancient burrows informs our understanding of current and projected future changes:
How do burrows of the past relate to our future, and perhaps hold the key to better predicting how we and the rest of life will adapt to a warming world? This is again where curiosity-driven research about how burrowing animals reacted to and survived mass extinctions in the geologic past might apply. For one, I predict that research on fossil burrows used originally to find fossil fuels will have its utility flipped. Instead, we will use these traces of past lives to discern climatic cycles, which in turn should help us better predict and prepare for the grimmest of climate change scenarios in our near future. (pp. 291–292)