The Rise of Mammals: From Dinosaurs to Dominance in Earth’s History
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Chapter 1: Transitioning from Dinosaurs to Mammals
In this ongoing exploration of Earth’s history, we have traced every 100 million-year segment from the planet's formation 4.6 billion years ago up to 100 million years ago. This journey has highlighted the emergence of the Sun, Moon, and Earth, along with the inception of life and the gradual increase in complexity. As we move closer to the present day, we now focus on the era where mammals finally take the spotlight, albeit not just yet.
During the latter part of the Cretaceous Period (145 to 66 million years ago), dinosaurs were still the reigning champions of the planet. Iconic species like Triceratops, Velociraptor, Ankylosaurus, and the formidable Tyrannosaurus rex dominated the landscape. T. Rex, which roamed the Earth approximately 72.7 million years ago, weighed around 8.8 tonnes and embodied pure ferocity. However, it was not the largest dinosaur; that title belonged to the gigantic herbivores known as titanosaurs, such as Patagotitan, which measured 35 meters in length and tipped the scales at a staggering 70 tonnes—longer than a blue whale and twice as heavy as a Brontosaurus.
Beasts Before Us: The Untold Story of Mammal Evolution
This video delves into the fascinating evolution of mammals, showcasing their rise in a world dominated by dinosaurs.
Section 1.1: The Floral and Faunal Changes
During this time, flowering plants began to proliferate, eventually becoming the predominant group of plants, comprising about 90% of all species today. This rapid growth coincided with the evolution of pollinators like bees, butterflies, and moths, forming a crucial ecological partnership.
As we look at the plant life, the first grasses emerged, marking a relatively recent development in Earth's botanical history. Alongside these grasses came the initial appearances of grasshoppers, ants, and aphids.
Subsection 1.1.1: The Catastrophic End of an Era
The Cretaceous Period met a sudden conclusion around 66 million years ago. The planet faced challenges due to greenhouse gases emitted by volcanic activity from the Deccan Traps in India. This period of instability was exacerbated when an asteroid, roughly the size of Bristol, struck the Earth, creating the Chicxulub crater, which spans 200 kilometers wide and 20 kilometers deep in the Yucatán Peninsula. This cataclysmic event led to the extinction of about 75% of all species.
Interestingly, while we often think of dinosaurs as creatures of the distant past, they only recently vanished from the Earth.
Section 1.2: The Legacy of Birds
Birds, which evolved from theropod dinosaurs, are direct descendants of these ancient creatures. Fascinatingly, there are currently more species of birds than mammals, with approximately 11,000 bird species compared to just 6,400 mammals. T. Rex itself can be whimsically compared to a large, wingless chicken—fierce yet undeniably linked to its avian descendants.
Chapter 2: The Ascendancy of Mammals
As we transition into the Paleogene (66 to 23 million years ago), Neogene (23 to 2.5 million years ago), and Quaternary Periods (2.5 million years ago to present), we observe that after each extinction event, the environmental landscape changes drastically. Newly available niches must be filled, and food webs need to be reestablished. This time, evolution favored mammals.
The Rise and Reign of the Mammals - with Steve Brusatte
In this insightful video, Steve Brusatte discusses the evolution and dominance of mammals following the extinction of the dinosaurs, highlighting their remarkable adaptability.
The defining characteristic of mammals, derived from the Latin word 'mamma,' refers to their unique mammary glands. Mammals can be categorized into three groups: monotremes, which lay eggs; marsupials, where young develop in pouches; and placentals, which carry young in their wombs. Though mammals first appeared around 225 million years ago, they were initially small and unremarkable. Interestingly, around 70% of all mammal species today are rodents, bats, or shrews.
However, some mammals grew to monumental sizes, evolving into creatures such as mastodons, saber-toothed tigers, and woolly rhinoceroses. Remarkably, about 52 million years ago, mammals even adapted to return to aquatic life, giving rise to dolphins and whales.
One Mammal to Rule Them All
Yet, it's not just size that matters in the animal kingdom; brain size plays a crucial role. This brings us to a certain small, mostly hairless, yet highly intelligent mammal that would come to dominate the planet...
This article represents Part 47 in a series of 50 that chronicles Earth's history, detailing significant events and changes over extensive periods. For those interested, you can also explore Part 46: DINOSAUR and Part 48: HUMANS. If you'd like to follow the entire series, please join me on this journey.