65 million years ago, the planet Earth was rocked by a catastrophic event; a giant asteroid
impact that wiped out the non-avian dinosaurs and many other species.
But from this devastation emerged a new world, one that would be shaped by the survivors
of the apocalypse.
In the aftermath of the extinction, mammals and other small creatures that had been lurking
in the shadows of the dinosaurs began to thrive and diversify, eventually giving rise to the
incredible range of life forms that we see on Earth today.
This new world was filled with strange and wonderful creatures, from giant birds and
carnivorous marsupials to saber-toothed cats and massive ground sloths.
In the oceans, ancient reptiles like the ichthyosaurs and plesiosaurs were replaced by new and formidable
predators, such as the fearsome megalodon shark.
The landscapes of the world were transformed as well, with vast grasslands and forests
spreading across the continents and providing new habitats for a host of different species.
Join us as we explore the Earth after the dinosaurs, a time of incredible change, innovation,
and survival.
[LOGO]
About a million years after the extinction of the dinosaurs, the Earth was a very different
place from what it is today.
During this time, known as the Paleogene period, the continents were still in the process of
moving and changing shape.
The planet was much warmer than it is now, with tropical forests spreading across the
globe, and the sea levels were much higher.
The early Paleogene was characterized by the proliferation of mammals, birds, and reptiles,
many of which were quite different from the species we see today.
The ecosystems of the time were also different, with different food webs and interactions
between species and began to evolve and adapt to the changing environments.
With the huge dinosaurs now out of the way, mammals could exploit the planet's resources
for themselves.
Within a few million years of the asteroid impact the fossil record shows an explosion
in mammalian diversity.
There is abundant fossil evidence for the evolution of shrew-like mammals called morganucodontids
that evolved into the mammals that we see today.
Some of the earliest known fossils of mammals are from the Jurassic period, around 165 million
years ago, and include small, insect-eating mammals similar in size and shape to modern-day
shrews.
One of these is a 200-million year old species named Megazostrodon, which measured about
10-12 centimeters [4 to 5 inches] long.
It most likely ate insects and small reptiles, and was probably nocturnal because it had
a larger brain, and the enlarged areas of its brain were discovered to be those that
process sounds and smells.
This evolutionary trait was likely to avoid being in competition with reptiles or becoming
prey to the dinosaurs.
It might be hard to believe but, all living mammals today, including us, descend from
this one line that survived.
In the oceans, the first animals to appear after the dinosaurs were ammonites, which
were relatives of the modern-day nautilus.
They were important predators in the ocean and helped to maintain balance in the marine
ecosystem.
In addition to mammals and ammonites, other early animals on Earth after the extinction
of the dinosaurs included birds, reptiles, and fish.
The early bird species were mostly small and similar in size to modern-day sparrows, while
the reptiles of the time included turtles, lizards, and snakes.
Fossil evidence shows that these early mammals changed in size and shape over time, as well
as in their adaptations to specific habitats and food sources.
For example, whales evolved from a terrestrial ancestor that lived around 50-52 million years
ago and gradually became better adapted to life in the water, until they became the fully
aquatic whales that we know today.
This animal is named Pakicetus, a four-legged creature about the size of a goat that scientists
now recognise as one of the first whales.
Although it had the body of a land animal, its head had the distinctive long skull shape
of a whale’s.
Over time, these animals adapted to the water and they lost their limbs, their nostrils
shifted backwards and upwards, and forelimbs turned into flippers, and of course, they
grew in size immensely.
Fossils of Pakicetus have been discovered in the Tethys Sea region, which was a shallow
sea that existed between the ancient continents of Gondwana and Laurasia.
During the Miocene epoch, the oceans were home to a variety of marine animals, including
many that are still present in the oceans today, such as dolphins, whales, sea lions,
seals, sea turtles, and various types of fish.
However, there were also many prehistoric marine animals that have since gone extinct.
Megalodon, a giant prehistoric shark, is thought to have first appeared about 23 million years
ago during the Miocene epoch.
Megalodon was a top predator in the oceans, and it is estimated to have grown up to 108
meters [60 feet] in length, making it one of the largest known sharks to have ever existed.
Some of the other prehistoric marine animals that were present in the oceans during the
time Megalodon was swimming around were creatures such as Basilosaurus which was a large prehistoric
whale that could grow longer than 15 meters [50 feet] in length and lived during the Eocene
epoch and is one of the earliest known whales.
There was another top predator in the oceans at the time, and it was something even bigger
than Megalodon.
We’re talking about Livyatan: A prehistoric whale that lived around 8-12 million years
ago during the Miocene epoch.
This whale is estimated to have been about 13 meters [43 feet] long and had massive teeth,
suggesting that it was a formidable predator.
The Livyatan is a close relative of modern sperm whales.
But there were more than just sharks and whales in the seas and oceans.
Dunkleosteus was a massive prehistoric fish that lived during the Devonian period, and
was known for its huge size, powerful jaws, and bony armor.
The infamous Mosasaurus that the Jurassic Park movies brought to life was a type of
marine reptile that lived during the Late Cretaceous period.
The largest fossil specimen measures a whopping 17 meters long [56 feet].
Mosasaurus had a long, streamlined body with four flippers and a powerful tail that allowed
it to swim rapidly through the water.
Its skull was elongated and had numerous sharp, pointed teeth, which it used to catch fish
and other prey.
But despite its size and fearsome appearance, Mosasaurus was not a dinosaur, but a type
of lizard, and is considered to be one of the largest and most successful marine reptiles
to have ever lived.
And then there was Archelon, a type of sea turtle that lived during the Late Cretaceous
period and was one of the largest known turtles to have ever existed.
These are just a handful of the many creatures that evolved and adapted to aquatic life.
But it was not just in the oceans that life diversified and exploded into many different
species.
There were many strange and bizarre looking creatures that appeared on land as well.
Creatures that lived on land such as rodents evolved from early, shrew-like mammals, and
diversified into a variety of species, including mice, rats, squirrels, beavers, and many others.
Carnivores also evolved from early, shrew-like mammals and gave rise to cats, dogs, bears,
and other predator species.
The earliest known members of the cat family, Felidae, are believed to have evolved from
a group of small, shrew-like mammals called miacids, which lived during the Paleocene
epoch, approximately 66 to 56 million years ago.
The miacids were a diverse group of carnivorous mammals that were adapted to hunting small
prey.
Modern day Mongooses can trace their origins to miacids.
Over time, some miacid species evolved specialized features that made them more efficient hunters,
such as retractable claws and more powerful jaws.
One of these specialized miacids, called Proailurus, is considered to be one of the earliest known
cat-like animals.
Proailurus lived during the Oligocene epoch, around 30 million years ago, and had several
features that are characteristic of modern cats, including retractable claws and a more
powerful bite.
Proailurus evolved and diversified, eventually giving rise to various lineages of cats with
different anatomical features, including the saber-toothed cats.
One of the most well-known groups of saber-toothed cats is the Smilodontini tribe, which included
Smilodon and Homotherium.
These cats were well known by their long, saber-like canine teeth, which were used for
hunting and possibly for defense against predators.
The earliest known members of the dog family, Canidae, are believed to have appeared during
the Eocene epoch, around 56 to 33.9 million years ago.
One of the earliest known canids is a small, fox-like animal called Hesperocyon, which
lived in what is now North America around 40 million years ago.
Hesperocyon is believed to be the ancestor of all modern canids, including dogs, wolves,
foxes, and coyotes.
But there were other predators aside from the prehistoric cats and dogs roaming the
plains.
Terror birds, also known as Phorusrhacids, are a group of large, flightless, predatory
birds that were native to the Americas approximately 2 million years after the extinction of the
dinosaurs.
The exact timing of the appearance of terror birds is not well established, but it is believed
to have been in the Late Paleocene or Early Eocene, about 62-58 million years ago.
Titanis walleri was one of the last and largest species of terror bird.
These birds dominated the continent for millions of years before going extinct around 1.8 million
years ago, possibly due to climate change and competition from other predators.
Titanis was likely a carnivorous bird that fed on a variety of prey that may have included
other birds, mammals, reptiles, and possibly even large insects and invertebrates.
Fossils of Titanis have been found in various locations in North and South America, and
some of the bones show signs of carnivorous feeding, including tooth marks and damage
caused by digestion.
It is interesting to note that while some modern birds are descendants of dinosaurs,
the Phorusrhacids are not.
They are a separate and distinct group of birds that evolved independently from dinosaurs
and belong to a group of flightless birds known as Palaeognathae, which also includes
the modern ostrich, emu, kiwi, and the cassowary which is the deadliest bird in the world.
But terror birds weren’t the only interesting and bizarre creatures to appear.
Several species of prehistoric sloths evolved and lived during the Cenozoic Era, which spans
from about 66 million years ago to the present day.
Ground sloths were the size of huge bears that lived from the Oligocene epoch to the
Pleistocene epoch, which spanned from about 33.9 million years ago to 11,700 years ago.
They were quadrupedal and had large claws that were likely used for defense and digging.
Tree sloths lived from the Oligocene epoch to the present day.
They were arboreal and had long limbs and curved claws that allowed them to move easily
through the trees.
Today, the only surviving species of tree sloth is the two-toed sloth and three-toed
sloth.
But ‘where are the snakes?’
You might be asking.
The evolutionary history of snakes is complex and not fully understood, but scientific evidence
suggests that snakes evolved from a group of small, lizard-like ancestors called ‘stem
squamates’ that lived more than 100 million years ago, during the time of the dinosaurs.
These early stem squamates were likely small, insect-eating creatures that lived on the
forest floor much like the early shrew-like creatures.
Over time, some of these stem squamates evolved becoming more elongate and legless.
The earliest known fossils of snakes, such as Eophis underwoodi, date back to around
95 million years ago and show features that are similar to those of modern snakes, such
as the presence of a flexible skull and a long, slender body.
Titanoboa would evolve from a small group of boas and is considered to be the largest
snake ever discovered, with the largest known specimens estimated to have reached lengths
of up to 12.8 meters [42 feet] long and weighed up to 1,135 kilograms [2,500 pounds].
So while snakes did not evolve directly from tiny shrew-like creatures, they did evolve
from small, lizard-like ancestors during the time of the dinosaurs, and have since evolved
to become the diverse group of animals that we know today.
And finally we come to our own ancestors…
Fossil evidence shows that early primates had small bodies, long tails, and grasping
hands and feet, adaptations that would have been useful for climbing and foraging for
food in trees.
Over time, primates evolved into the diverse group of primates that we have today, including
monkeys, apes, and humans.
But there’s so much to cover about our own species, and we’d need more time.
So if you want to see that in another video, let us know in the comments.
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