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. If you enjoyed the video, show some support
with a like, we appreciate it, and make sure to subscribe to stay tuned here for more videos
in the series! Thanks for watching!
