How did little, fuzzy creatures that ran beneath the feet of dinosaurs come to control the world?

The evolutionary history of mammals is explored in-depth in a recently published book.

Soon after the first dinosaurs appeared during the Triassic period, small hairy mammals began to emerge from the ground and start scurrying about. These mammals had formidable teeth that they used to gnaw on plants, insects, and eventually dinosaurs. But where did these creatures with a body temperature above freezing come from? How did they avoid being killed by the massive asteroid that collided with Earth 66 million years ago, wiping out all of the dinosaurs that were not birds? How are mammalian species currently faring, especially in light of the impending threats?

Paleontologist Steve Brusatte addresses all of these concerns and more in his new book, "The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us," which was published by Mariner Books on Tuesday (June 7). Very few people are better equipped to tell this story than Brusatte, the chair of paleontology and evolution at the University of Edinburgh in Scotland. Brusatte's first book, "The Rise and Fall of the Dinosaurs: A New History of a Lost World" (Mariner Books, 2018), connected readers with a wide variety of scientists and their numerous discoveries regarding the time of the dinosaurs.

Brusatte delves into the mammalian lineage, returning to the synapsids in his latest book. Synapsids were an odd group of animals that existed during the Carboniferous period (359 million to 299 million years ago) and eventually developed into mammals. He follows the evolution of mammals up to the present day, offering exciting anecdotes along the way (for example, did you know that the bones in mammals' ears were previously a part of their jaws?). as well as introducing readers to the researchers who were instrumental in developing the field of mammology into what it is today.

But don't just take our word for it. In an email Q&A about his work that Live Science conducted with Brusatte, you can discover more about his new book directly from Brusatte himself. The comments provided by Brusatte have been modified very little for clarity.

Since the topic of your newest book is mammals, I feel compelled to ask: What became of the dinosaurs? You have consistently been recognized for your exceptional studies on dinosaurs, and you are even serving as the paleontology advisor for the upcoming film "Jurassic World: Dominion" (Universal Pictures, 2022). What was it about mammals that piqued your interest?

I have always been and will continue to be very interested in dinosaurs. My first job out of college was in paleontology, and I've devoted the better part of the last two decades to studying dinosaurs. However, the more I've worked on the history of dinosaurs—as I've followed them from their beginnings, through their expansion into monstrous sizes, and finally to their extinction—the more naturally I've begun to wonder what occurred after dinosaurs became extinct. How did mammals succeed in dinosaurs as the dominant species? And in the end, I realized that it is just as fascinating a story as the evolution of dinosaurs. After all, we belong to the mammalian kingdom. This, then, is our history: the account of our most profound beginnings, of our forebears, of how our relatives have persisted for more than 325 million years, and of everything that the Earth and the cosmos have done to us.

The history of mammals goes back very far. What were some pre-mammal species like, and when did they inhabit the Earth before animals developed into mammals?

The story of mammals begins about 325 million years ago, during the Carboniferous period, a humid realm of coal swamps, the time of the first jungles, and an age in which dragonflies were the size of pigeons and millipedes were more extensive than humans. During this time, dragonflies were the size of millipedes and were more extensive than humans. In these swamps, an unremarkable scaly creature had two halves split apart. The lineage that eventually gave rise to lizards, crocodiles, dinosaurs, and birds originated from one family tree branch. The other branch had an evolutionary change that resulted in a large hole developing behind the eye to attach powerful jaw muscles. These creatures were known as synapsids. They would evolve into mammals in the long run.

These animals, which eventually gave rise to the lineage of mammals, evolved characteristics of modern mammals, such as hair, warm-bloodedness (endothermy), strong jaw muscles and bites, and so on. What other ways did these modifications help them survive, and how did those help them thrive?

Early synapsids were put through a lot of hardships. They formed in the dampness of the coal swamps, but as all of the land masses collided to form the supercontinent Pangea, the jungles died out, and a large portion of the Earth turned into a scorching desert. Then, approximately 252 million years ago, there was a cataclysmic mass extinction, considered the worst time of mass mortality in the history of the Earth. This occurred due to gigantic volcanoes erupting in Siberia, which caused global warming.

Despite everything, the synapsids managed to survive and adapt. Because they needed to keep their bodies warm, they developed hair. Instead of placing their trust in the capricious vagaries of their surroundings, they evolved to become warm-blooded, which gave them an internal furnace that regulated the temperature of their bodies. Their jaw muscles got enormous, and their teeth changed from the bare steak blades of their predecessors into a complex array of canines, incisors, premolars, and molars that we're able to grasp, slice, pulverize, and chew the food they consumed. They evolved large brains, a keen intelligence, and acute senses of smell and hearing in addition to their already impressive intelligence. They were able to adapt to their surroundings and weather the storms of their early history because of all of these factors, which made them more adaptable than their forefathers.

What is the oldest mammal that has ever been documented? What made it stand out from the rest of its pre-mammal cousins and make it unique?

Pangea, a supercontinent roughly 225 million years ago, was home to the first actual animals. This period is known as the Triassic. These were tiny, nearly unremarkable creatures, and if you came across one, you would almost certainly mistake it for a mouse. They appeared to be particularly submissive when contrasted with the other animals emerging with them simultaneously, including dinosaurs.

But don't be fooled by the fact that animals are typically relatively small. They were quick, intelligent, and able to adjust on the fly. Their more straightforward jaw structure was the primary trait that distinguished them from their forebears. Mammals have only one bone in their jaws called the dentary, in contrast to their ancestors, who had several smaller bones. A singular anchor for the entirety of the teeth as well as the muscles of the jaw. It's excellent for taking substantial bites. Ideal for taking bites that can be precisely timed to subdue prey and eat food. And what became of those extra jaw bones once they were no longer necessary for the process of feeding? They shrunk in size and went inside the ear, where they assisted these mammals—and their descendants, like us!—in transmitting sound from the eardrum to the cochlea. Because of this, our hearing is superior compared to the vast majority of other species.

Early mammals were relatively small species ranging in size from shrews to possums for hundreds of millions of years. Why were they so small, and when exactly did mammals start growing to their adult size?

During the Triassic, Jurassic, and Cretaceous periods, mammals coexisted with dinosaurs for over 150 million years. During this entire period, we are unaware of any mammal growing to be larger than a badger. They remained diminutive because of the dinosaurs. Because animals had little space to expand their range, they were forced to live in the shadows. However, they made the underworld their own by controlling it. They branched into many other species, including scurriers, climbers, diggers, swimmers, and even gliders with skin wings. Because these early mammals were so skilled at hiding in plain sight, they prevented the size of dinosaurs from decreasing through time. There was never a Tyrannosaurus rex that was the size of a mouse, nor was there a Brontosaurus, the size of a rat. This is because mammals quickly filled those niches and never gave them up.

It's hard to believe that mammals first appeared during the time of the dinosaurs, but they did. According to the fossil evidence, how did the two interact?

Dinosaurs ensured that mammoths remained modest in size. Mammals were essential to the growth of dinosaurs. For tens of millions of years, it essentially remained in a state of evolutionary equilibrium. But there is one incredible fossil that was discovered in China, and it is from a mammal that lived during the Cretaceous period and was called Repenomamus. This mammal was about the size of a lapdog. It was buried so swiftly and transformed into a fossil so quickly that the remains of its final meal, dinosaur bones, were preserved in its stomach. This occurred because the process happened so fast. This mammal started its day by chowing down on newborn dinosaurs. Certain dinosaurs would not have survived if mammals had been there!

How on Earth did mammals survive the impact of the asteroid that took place 66 million years ago on our planet?

An asteroid the size of Mount Everest was aimlessly hurtling through the heavens sixty-six million years ago, and it just so happened to make a beeline for the Earth. This asteroid is widely believed to be responsible for the extinction of the dinosaurs. It slammed into the ground with the energy equivalent of more than a billion nuclear bombs. It carved a crater over 100 miles (160 kilometers) wide in Mexico and penetrated the Earth's crust more than 100 miles (160 kilometers) deep.

I am confident in saying that today was the single worst day in the entire course of my existence. Tsunamis, earthquakes, wildfires, winds, dust obscuring the light, fading trees, and the collapse of ecosystems are all potential outcomes of climate change. The dinosaurs could not adapt, and they all perished except for a few bird species. The answer is yes; there are still mammals around today. But what the vast majority of people don't realize is that the same fate nearly befell mammals as it did dinosaurs. According to our best estimates, approximately 90% of all animals died. Only a handful of brave individuals managed to escape the ordeal alive. These were animals on the smaller side, which allowed them to burrow and hide more efficiently, and they were omnivorous, which meant they could consume a wide variety of foods. One of our forefathers was found to be among those people. If it had not survived the destruction caused by the asteroid, this dialogue would not be taking place, and we would not be here.

What kinds of mammals came into existence after the extinction of the dinosaurs (with the apparent exception of birds)?

Imagine that instead of your feet, you were the tiny, furry paws of our mouse-sized ancestor who made it through the asteroid's devastation. The globe appeared to be a lonely place all of a sudden. The T. rex had vanished. The triceratops had vanished. Ecosystems were wide open. There were plenty of opportunities. The mammals jumped on the chance right away. It is essential to remember that during the more than 150 million years that dinosaurs coexisted with mammals, no mammal ever grew more significant than a badger. After that, there were animals the size of pigs within just a few hundred thousand years of the extinction of the dinosaurs. Around one million years from now, there will be mammals the size of cows! And it was from these mammals that many of our most common ancestors descended, including horses, dogs, monkeys, bats, and whales.

What do you consider to be one of the most peculiar mammals that have since been extinct?

There were once woolly elephants and rhinos, armadillos the size of Volkswagens, deer with antlers larger than a dining room table, strange beasts called chalicotheres that looked like an unholy hybrid of a horse and a gorilla, "thunder beasts" called brontotheres with battering-ram horns, and rhinos that did not have horns but weighed around 20 tons [18 metric tons] — the giant mammals to ever live on land. There is no living example of any of these things now.

Our human predecessors would have encountered, interacted with, and hunted some of them. In my book, you will get to know each of them individually. The vast ground sloths that lived during the ice age are the extinct creatures that come to mind when I think of the most bizarre animals that have since become extinct. These days, sloths are typically quite cute and cuddly. They are slacking off. They are adorable. However, only approximately 10,000 years ago, some sloths were taller than 10 feet (3 meters) and had claws that resembled Edward Scissorhands'. They could have glanced into a window on the second story without even trying or dunked a basketball without even attempting it. How could it possibly be any stranger than that?

When did the first primates appear, and what were some of their distinguishing characteristics?

We didn't start to find evidence of baby teeth in the fossil record for at least another 100,000 years after the asteroid that caused the extinction of the dinosaurs. They do not have any jagged peaks or ridges but relatively smooth, rounded edges, making them ideal for eating fruits. They are known as Purgatorius, the primate with the most extended evolutionary history. It would appear that monkeys were one of the first mammals to take advantage of the extinction of the dinosaurs to broaden their range and increase their genetic diversity.

However, evidence derived from DNA suggests that primates may have had a more extensive past. They, or rather, I should say that we have so many mutations in our DNA that if we did a back-calculation based on the known rates of DNA change in the present day, we would predict that primates originated alongside dinosaurs in the Cretaceous period. This would be the case if we used known rates of DNA change in the present day. However, we have not yet located any fossils of them. Is it possible that the results of the DNA test were inaccurate? Or maybe we haven't looked for fossils in the correct places because we don't know where to look. I am inclined to believe the latter, and I think whoever discovers the first genuine Cretaceous ape will achieve a great deal of notoriety in paleontology.

Let's talk about the history of the human race. What environmental and climatic shifts were taking place at the same time that early people were evolving?

In the book, I try not to concentrate on human beings. I don't want to make this situation about the two of us. In the end, humans are just one of many magnificent groups of mammalian species that have developed over time. Whales eventually grew to be the largest animals that have ever lived. Modern blue whales are even more significant than submarines. Bats were able to take flight after transforming their arms into wings. The bodies of elephants and rhinos became significantly more important over time, and they developed the most spectacular teeth and tusks. And the items on the list continue. Therefore, I don't want to give the impression that humans are the inescapable pinnacle of mammalian evolution and that the entire 325 million years of synapsid history was just a prelude that led up to us in a friendly and tidy package. That is far too straightforward of a narrative. However, it is equally important to acknowledge that humans are amazing creatures. We have developed giant brains, consciousness, the ability to collaborate with others, the capacity to mold the world in myriad ways, and even the capacity to tame and clone other mammals.

Our journey as humans began 5 and 7 million years ago when our ancestors diverged from other apes that eventually evolved into chimpanzees. This event marked the beginning of our journey. Before our minds grew to be highly complex and we developed the ability to fashion tools out of stone, we started walking upright. And all of this was taking place simultaneously as the climate was shifting and forests in Africa, our historic homeland, were succumbing to deforestation and being replaced by grasslands. At least, that's how the tale goes. Even though this turns out to be a bit too simplistic, the real story is significantly more profound, complicated, and enjoyable. And if you want to know the answer, you'll have to read the book!

The human race is currently at a critical juncture, particularly about the climate change humans produce. What might happen to mammals in the future based on what we know from fossils of mammalian species that lived through times of climate change?

Currently, mammals are in their most precarious position since confronting the asteroid 66 million years ago. This also means that we are at our most precarious point. And, as much as it pains me to say it, the reason for all this is that one species of mammal has had such a negative effect on the other 6000 or more species of mammals, and that species is us. The pace at which we are affecting global change is astounding. We engage in activities such as hunting, clearing land, converting forested areas into farming, releasing greenhouse gases into the atmosphere that contribute to the warming of the Earth, and a great deal more. We undoubtedly played a significant role in the extinction of many of the fascinating "megafauna" that lived throughout the Ice Age, such as the woolly mammoth and the saber-toothed tiger. We hunted them, damaged their habitats, and fragmented their populations.

At least 350 mammal species have become extinct since Homo sapiens began their march across the globe, accounting for approximately 5% of all mammal species. It may not seem significant, but if we keep going at this rate, half of all animals may become extinct in the not-too-distant future. There is a considerable amount of uncertainty there. I don't want to come across as pessimistic or overly confident about the future because it's difficult to anticipate what will happen.

What I am aware of, though, is that we humans have developed large brains, incredible intelligence, and the capacity to cooperate. We are mindful of the damage we are causing to our world, and we can devise solutions. Saber-toothed cats and numerous other extinct creatures never possessed the same powers to change or improve the planet. We do. It is up to us to decide what steps to take next.

 

 

Article source :  https://www.livescience.com/rise-reign-mammals-steve-brusatte-book

Image source :  https://pixabay.com/id/vectors/dinosaurus-tyrannosaurus-rex-hitam-309638/

# How the planet came to be ruled by tiny, hairy creatures that used to scurry around under the feet of dinosaurs

# How little, hairy creatures that scuttled beneath the dinosaurs' feet became the dominant species

# How did little, fuzzy creatures that ran beneath the feet of dinosaurs come to control the world?