The Evolution Underground

A fascinating book that looks at burrows and a number of animals that make and live in them. Through various examples in the book, the author shows that burrows are not only an effective way to protect various animals from changes in the environment, but also a way for animals to change and engineer the environment to suit themselves. The chapters in the book makes up about half the book, with the rest given over to lots of endnotes and references. The numerous endnotes shows the amount of research and fact checking done to ensure that what is written in the book is supported by evidence and not just speculation on the author's part. And where there is speculation, the author points it out.

The first chapter gives an overview of what the book will cover. Starting with an expedition with undergraduates to examine burrows that alligators use, including one that has an unexpected alligator in it, the author then mentions why burrows are important for the survival of not just the alligators but also for a whole host of animals not just in the present but also in the past, including the ancestors of mammals. Burrows serve to insulate animals from changes in the environment, like temperature changes, fires and even possible extinction events.

Chapter Two looks at how human used burrows. The author uses the fascinating example of various underground cities he explored while on a trip to Turkey as the main example. He shows how humans at the time dug into the soft rocks of the region of Turkey to carve out living spaces for themselves and to shelter animals, as well as to preserve fruits and other food planted nearby. The underground cities also served as a form of defence from invading armies. Tunnels between cities were dug and used as transportation. Other more modern examples of underground living are then given, in the form of shelters against nuclear weapons. The author then speculates that burrowing animals like ants, badgers and moles might have provided examples for humans to emulate when planning such underground living quarters.

Chapter Three examines the burrows created by Gopher tortoises. These remarkable reptiles dig out burrows to live in, to procreate, and to protect themselves against the harsh environment. But the burrows don't just serve tortoises. A large variety of animals (over 400 recorded species) have been discovered to use the tortoise burrows, ranging from invertebrates to reptiles and mammals. Some of them are temporary residents, others are permanent. Some just use the burrows, while others dig and extend the burrows for their own use. The large number of burrows thus act as an ecosystem, earning the gopher tortoises the title of ecosystem engineers. The burrows not only support an entire ecosystem, they also serve to modify the landscape, aerate and turn over the soil. In general, the burrow systems help made the landscape a more hospitable place for the gophers themselves and the host of animals that depend on the burrows.

Chapter Four looks at whether burrows might have been used by dinosaurs. The answer is probably yes. The author describes one of the first burrowing dinosaurs he helped discovered, as well as the trace fossil of the burrow probably dug by the dinosaur. The descendants of the dinosaurs, the birds, would also make and use burrows. While most birds live in high places or on the ground, some birds like penguins, the burrowing owl, a parrot, kingfishers and bee eaters do use (and make) burrows.

Chapter Five is a somewhat speculative look at how burrowing animals survived the various global catastrophes that have marked the various ages of the Earth. It starts with a speculative story involving a Lystrosaurus, an early kind of synapsid (synapsids are an ancestor to all mammals), surviving the climate change that marked the change from the Permian to Triassic period. Surviving in the changed environment would involve burrowing to protect itself from the environment. But as the number of surviving Lystrosaurus grow in the area, they become an ecosystem engineer, changing the environment via their burrows to suit themselves. Other major environmental catastrophes at the end of the Triassic and the end of the Cretaceous periods are also covered. And at each once, the author makes a point that burrows offer one way for animals to survive the catastrophes, and to then repopulate the world with new species of animals.

Chapter Six looks at how burrowing might help marine animals survive the harshness of surviving out of water. It starts by looking at trilobites fossils and their burrows, particularly those found in what appears to be the fossil remains of a river, which is unusual for a marine species. It is only by examining the environment closer that the author finally makes the right conclusion; that the river is an estuary (where the river meets the sea), and that the trilobites were living and burrowing in a salty environment. He then moves on to the modern example of the horseshoe crab, whose lifestyle resembles those of the trilobites, by coming out on to land and burrowing into the sandy soil to lay their eggs and to hide themselves. Another example of a marine species surviving on land presented is the lungfish, which is able to burrow and hibernate when their watery environment dries up. Burrows would also serve to protect amphibians from the environment, and do it well enough that amphibians can be found even in the frozen arctic. The chapter closes by looking at iguanas that can survive hurricanes and storms using burrows, and pointing to evidence that modern snakes evolved from burrowing snake ancestors.

Chapter Seven looks at when burrowing might have begun by looking at the trace fossils of the Ediacaran lifeforms. The evidence shows that these organisms did not have the ability to dig burrows into the bacterial mats that line the sea floor. It is only when life began to acquire shells and other hard parts (like teeth and claws) in the Cambrian era that evidence of burrows began to be seen. Shells are also seen as evidence that some creatures were protecting themselves against predators, starting a never ending arms-race between the prey and predators. In this race, burrows would prove to be one defensive method that would be used by many life forms.

Chapter Eight looks at the various invertebrates that burrow, starting with the one probably best known to most people: earthworms. Earthworms turn out to be amazing burrowers, able to dig deep. More over, they are so numerous that studies have shown that they can collectively move tons of soil from underground and act as very effective ecosystem engineers. Ants are also featured, burrowing deep underground and digging out vast underground cities. Other larger invertebrates like lobsters, crayfish, crabs and shrimps are also featured, each other showing that while they are individually small, collectively they are very efficient at moving soil and changing the ecosystem they live in to suit themselves.

Chapter Nine opens with the eruption of Mount St. Helens and the devastation the eruption causes to the surrounding region. By now, you would not be surprised to learn that some animals survived the eruption and most of them would be those that were in burrows during the eruption, especially the pocket gophers whose burrows would not only protect them, but help to revive the forest by saving other animals and seeds that would rejuvenate the areas. The naked mole rat is also featured, as well as their unusual social structure that resembles the social ants. The largest burrowers known are also featured: the extinct giant ground sloth from South America was well as bears. Coming to the present, the author talks about the current environmental crisis and extinctions and makes the case the burrowing animals are a vital part of the environment and plans to try to save and preserve the environment should also consider the burrowing creatures.