Field of Science

Book Review: "The Rise and Reign of the Mammals: A New History, From the Shadows of the Dinosaurs to US", by Steve Brusatte

A terrific book by Edinburgh paleontologist Steve Brusatte on the rise of the mammals. Engaging, personal and packed with simple explanations and analogies. Brusatte tracks the evolution of mammals from about 325 million years ago when our reptilian answers split off into two groups - the synapsids and the diapsids. The diapsids gave rise to reptiles like crocodiles and snakes while the synapsids eventually gave rise to us. The synapsids evolved with a hole behind their eye socket: it’s now covered with a set of muscles which you can feel if you touch your cheek while chewing.

Much of the book is focused on how mammals evolved different anatomical and physiological functions against the backdrop of catastrophic and gentle climate change, including the shifting of the continents and major extinctions driven by volcanic eruptions, meteors (during the K-T extinction event that killed the dinosaurs) sea level rises and ice ages. That mammals survived these upheavals is partly a result of chance and partly a result of some remarkable adaptations which the author spends considerable time describing. These adaptations include milk production, temperature regulation, hair, bigger brains and stable locomotion, among others.
Some these changes were simple but significant - for instance, a law named Carrier’s law limits lung capacity in slithering reptiles because each lung alternately gets compressed during sidewinding motions. When mammalian ancestors were able to lift their body upward from the ground and able to install a set of bones that constrained the rib cage, it allowed their lungs to be able to breathe and expel oxygen during movement and when the animal was eating. Needless to say, the ability to breathe and move while eating was momentous for survival in an environment in which predators abounded.
Another adaptation was the development of a specialized set of teeth that mark all mammals including humans - the incisors, canines, pre-molars and molars. Because these teeth form a specialized, complex apparatus, they emerge only twice in mammals - once during infancy and one more time during adulthood. But out chewing apparatus gave rise to another remarkable adaptation - in an evolutionary migration spread out over millions of years, bones of the jaw became the bones of the ear. The ear bones are a set of finely orchestrated and sensitive sound detectors that gave mammals an acute sense of hearing and enabled them to seek out mates and avoid predators.
Quite naturally, the book spends a good amount of time describing the mystery of why mammals survived the great meteor extinction of dinosaurs and much of other life on the planet. Except that it’s no mystery. Dinosaurs were bulky and specialized cold-blooded eaters which were exposed. Mammals were furry, rodent-like warm-blooded omnivores which could hide out underground and eke out an existence on charred vegetation and dead flesh in the post-apocalyptic environment. After the K-T event, there was no turning back for mammals.
The rest of the book spends time discussing particular features of mammalian evolution like flight in bats and the odd monotremes like the duck-billed platypus which lay eggs. A particularly memorable discussion is of the whales, the biggest mammals which have ever lived, which actually evolved from land mammals that would occasionally take to water to escape predators and seek out new food. With their exceptionally big brains and bat-like echolocation, whales remain a wonder of nature.
Brusatte also spices up his account with adventurous stories of intrepid paleontologists and archeologists who have dup up pioneering fossils in extreme environments ranging from the blistering tropical forests of Africa to the Gobi desert of Mongolia. Paleontology comes across as a truly international endeavor, with Chinese paleontologists especially making significant contributions; they were among the first for instance to discover a feather dinosaur, attesting to the reptile to bird evolutionary transition. Unlike old times when Victorian men did most of the digging, women are now a healthy percentage of the field.
Human evolution occupies only a few chapters of Brusatte’s book, and for good reason. While humans occupy a unique niche because of their intelligence, evolutionarily they are no more special or fascinating than whales, bats, platypuses, elephants or indeed the earliest synapsids. What we can take heart from is the fact that we are part of an unbroken thread of evolution ranging across all these creatures. Mammals have survived catastrophic extinctions and climate change events. Humans are now being responsible for one. Whether they are responsible for their own extinction or show the kind of adaptability that their ancestors showed is a future state only they are responsible for.

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