Rule, Mammalia

Dinosaurs loom large in the archaeology of eons ago. But the story of mammals can be traced back to that era. A readable romp through millions of years of evolution is provided by paleontologist Steve Brusatte in his latest book, The Rise and Reign of the Mammals. The story begins over 300 million years ago with a split between the ancestors of reptiles (diapsids) and mammals (synapsids). In the heyday of the dinosaurs, tiny mammals have proliferated, running around and getting their food while avoiding being stepped on or eaten by their larger reptilian cousins. They burrow, they hunt at night, and have poor color vision. But then an asteroid comes along, causes massive global environmental change, and the mammals rise to conquer the earth.

 

What makes a mammal? The name comes from the mammary glands. Nutritious food for the young. We are also characterized by fur and hair. Apparently, woolly mammoths sported many different colors, somewhat like the hairs of our human heads. And one characteristic that I hadn’t thought about much, but Brusatte goes into significant detail, are the three bones that make up the ear. You don’t find these in present-day reptiles or in birds, the descendants of the dinosaurs.

 

I had not counted on the importance of dentition in tracing the evolution of mammals, although as someone who has played Bios Megafauna, perhaps I should have paid more attention. Brusatte remedies the gaps in my knowledge with his extensive discussion of the size and shape of teeth and the diets of our many mammalian ancestors. I admit to skimming some of these parts, but otherwise I found the book to be engaging and very readable. There are creatures familiar to me, and others I had never heard of that were strange in more ways than one.

 

What stands out in the evolution of the mammals from the Eocene to the present day is the key role played by climate change. As temperature, humidity (or aridity), and oxygen levels alter the landscape and its flora, sources of sustenance change and wreak havoc on the food web. Creatures have to adapt or face extinction. Some succeed, others fail. The kings and apex predators of yesteryear have given way to the new ruler of Mammalia, us human beings. But we are now entering a season where global temperatures are changing faster than they ever have. Will we adapt? Or is this our twilight? What will a future archaeologist or perhaps an extra-terrestial have to say about our rise and reign? Will it simply be a blip in our planet’s evolutionary history? Will life retreat back to the ocean?

 

The largest creature that has ever lived on our planet is alive today. The blue whale. Greatest denizen of the oceans and a member of Mammalia. Will they survive the latest onslaught? Who will be the new ruler of the waves?