Book: The Rise And Reign of Mammals by Steve Brusatte
Krishna
We reviewed and liked very much this author’s earlier work, The Rise and Fall of the Dinosaurs.
The book starts with the end of dinosaurs and how mammals peeked out scurrying around. The author brings the same passion he showed in his earlier book which we have reviewed about the dinosaurs, The Rise and Fall of Dinosaurs, to this book too, only about the mammals. It is a treat to read of the now extinct and fairly weird mammal species that existed in the distant past but has now gone extinct. (Many known ones like Mammoths and Sabre Toothed Tiger and some unknown like dire wolf, and even more bizarre animals).
At the start there was this animal with a sail on its back, the better known Dimetrodon. Though it looked a bit like the dinosaurs, it was very different and was the start of the mammalian branch. Another similar animal Edephosaurus, which was one of the first vegetarian species – also a mammal. They were called pelycosaurs and were the start of the mammal lineage after the Permean era (where life was nearly wiped out in a big extinction). And there were caseids, which had tiny head and bloated body and looked like a caricature rather than a real animal – it was also vegetarian. Naturally, Edaphosaurus and caseids, eatling plants, became in turn food for carnivores like Dimetrodon. But pelycosaur numbers dwindled by climate change ice cap melting and the diversity declined during the middle of Permian period (273 million years ago). A new organism called therapsid emerged to take advantage of the new environment. In South Africa fossils of that period were found which seem to denote a strange animal called dicynodon, which seems to be a reptile-like head capped by a beak but also having canine tusks!!
They dominated the world during mid Permian period (prior to dinosaurs) and also started evolving warm bloodedness. As a prerequisite, they also grew hair to prevent heat loss.
Steve summarizes all life thus – remember it is over a period of billions of years – bacteria forms first, then joins to form complex organisms, which evolved into vertebrates – molluscs, clams, sea urchins, shrimp and crabs. Fishes evolved from first vertebrates. Then they split into therapsids, forerunners of mammals and another branch – therapsid – evolving into reptiles. A fascinating, but concise summary.
Permian period mass extinction was due to massive volcanic eruptions of a size unimaginable today. It killed more than 96% of the species existing then! Several plant eating dicynodonts thrived before the mass extinction. They fed the small carnivorous biarmosuchus (belonging to therapsid family). The larger gorgonopsians were the apex predators then. This had sabre tooth and a flexible jaw that opened wide to eat large prey. They became extinct as a part of Permian extinction.
Oligokyphus is an animal that thrived thereafter. The mammals got progressively tinier as the conditions changed. They survived multiple catastrophes that way. They were mostly rat or mouse size vermin in the Triassic period. Oligokyphus was an exception as it needed a bigger gut to digest plants, being a herbivore. They had to compete with non mammals like turtles, lizards, and crocodiles. And a huge reptile was beginning to spread. Dinosaurs.
The dinosaurs initially were battling crocodiles for supremacy. Both were growing bigger in a biological arms race. The surviving small mammals (cynodonts) may have become nocturnal as an added precaution. These mammalian ancestors may have thus lost the keen sense of sight, using smell, touch and hearing for navigation and hunting.
Most mammals can’t see colour either, which is why most have drab brown, tan or gray fur. At the end of Triassic, there was another huge lava eruption and another mass extinction – 30% of the species became extinct, among them early mammals like the tusked dicynodonts. The dinosaurs, though, survived into the Jurassic era. Among the victims were Lisowicia, a plant eater the size of elephants.
The fact that huge dinosaurs survived this extinction period is true but the causes are shrouded in mystery. The dinosaurs got bigger in a newly empty world where they were apex predators and diversified. The mammals stayed small and also thrived in the niches the dinosaurs could not get to.
One of the biggest learning for me is the negation of my earlier views. I mostly thought that while dinosaurs lived, the mammals could not thrive, even though they survived and it is the extinction of dinosaurs that paved the way for mammalian hegemony thereafter. This book describes how the mammals thrived all through the dinosaur period. Yes, they did not dominate and stayed small until after the dinosaurs as they could not outmatch the dinosaurs in their strength and ferocity but thrive they did in specific niches. This was an eye opener for me.
The book goes off into tangents that are still of interest for dedicated paleontologists but loses lay readers like me. Page after page of who found what fossils and how they became famous is monotonous and so are (with apologies) of the author’s expeditions and meetings of people of the same profession across the world. The book could have done without these, with no loss of information – at least for lay readers. It may have tightened the pace a lot more, as a bonus.
But there is enough to keep your interest and astonish you. You learn for example that whales are mammals (yes, most of us know that already) and in particular, placental mammals. Therefore whales have belly buttons! Also at least according to fossil evidence found so far, whales evolved from land mammals to fully aquatic animals from India, which was an island for most of this transformation.
We also learn that dolphins are a form of whales – or at least diverged from whales later. The whales split into two types and the toothed whales (sperm, killer, dolphins, narwahls etc) also developed echolocation and the toothless baleen whales (blue, humpback) diverged losing their teeth.
Echolocation filled the need for finding prey in dark oceans so well that the whales did not need, and thereby lost, their sense of smell! And whales have proportionately larger brain than most animals and are considered very intelligent creatures. Prehistoric whales were even more scary. The Livyatan was sixty feet long and could swallow an apex predator (T Rex) whole – we are only talking about the size of its mouth and not a battle between the two! Baleen whales grew to an even larger size but were toothless. They had baleen or strings of keratin to catch food thrugh the filter when they take in water in their mouths. So they don’t have, and don’t need, echolocation.
We learn that elephants grew fan like ears to be able to dissipate body heat better in warm climes where they live. In contract, the wooly mammoth, which lived in Siberia, has small ears to conserve body heat! The hairs on these beasts was also variable from blond to orange to brown to black! Some hairs were nearly transparent while others were bi coloured, with a mishmash of colours on the same strand!
And Mammoths are more closely related to Indian elephants than African elephants.
The author turns his attention last to one of the mammals. Us. He starts with hominids who were precursors to homo species (that includes us) and talks of the first hominids. It (we?) was concentrated in Africa and was diversified into multiple hominid species. They are the first ones to use crude stone tools. They are the first ones to start eating meat (as opposed to insects and leaves)
Homo species originated thereafter and they were the first ones (homo erectus to be precise) to leave the African homeland and spread. The tools got more sophisticated and it spread over multiple continents. Homo erectus met Australopithicus (another biped) before they became extinct. They were not stopped by the sea after spreading from Africa to Middle East and Asia. They built watercraft and crossed seas! They became multiple species. Homo Luzonensis in Philippines; homo floresiensis in Indonesia. Some of them shrunk, and became dwarf-like in size.
Homo Sapiens evolved from the Homo species before them, also in Africa and started spreading. They went father – into South America, into Pacific islands, and even Australia.
Among the previous homo species were two well known groups – Neanderthals in Europe and Denisovans in Asia. They were not primitive; Neanderthals were bright; they created artwork, cared for the sick and mourned the dead. They tamed fire; created spiritual structures.
To hear Steve tell the story, the neolithic age where we domesticated animals (starting with wild wolves in Siberia which we tamed into dogs) and agriculture (‘the taming of plants’) occurred much later then the extinction of the rival homo species including Neanderthals and Denisovans.
He goes philosophical and slightly maudlin contemplating the future of mammals and even us, with all the destruction that humans have done to the biodiversity and environment. It does feel right to end the book thus.
All in all, a good book to read and enlightens us while entertaining us.
7/10
— Krishna