• Paleogene Period

The Paleogene period is known for having marked the rise of mammals on our planet. In the same way the continents began to shape themselves towards the state they have today. Let’s find out what other changes accompanied this time.

What is the Paleogene period?

This is the first of the three periods of the Cenozoic era. It represents less than 1% of the geological time studied. However, rocks from this span were deposited recently and are found at or near the surface.

They are rocks that have not undergone much modification unlike many others that have the appearance of deposits. This facilitates access and interpretation for rocks from previous eras. That is why scientists have been able to learn a lot from them.

When it started?

This period gave beginning 65.5 million years BC. These were times during which sea levels fell, exposing dry land in North America, Africa and Australia. On the other hand, South America was left adrift in its own “ark”, since its birds, mammals and reptiles had their own evolution.

When I finish?

The end of this time came 23 million years ago BC, before the beginning of the Neogene period. Mammals managed to develop in size, number and diversity. By the time this time passed the life forms we know today filled the seas, and also gained dominion over the land.

Why is it called Paleogene?

The name of this period has origins in Greek and its meaning is born in ancient times. It is composed of palaios which means ancient and primitive time and therefore geno which means to generate or produce. It is a term introduced by German geologist Carl Friedrich Nauman in his book Lehrbuch der Geognosie of 1858.

What happened during the Paleogene period?

Emergence of mammals

During the Paleogene, mammals developed. Although they had coexisted during the last 100 million years of the Cretaceous with the dinosaurs, then they did not reach large sizes nor had they managed to diversify. When the reptilian tyrants disappeared, then they came to prosper and develop fully.

Fossil studies show that within about 10 million years of the Cretaceous extinction, already There were about 130 genera of mammals. These included bats, primates, rodents and whales, among many other animals that we already know today.

There is a greater understanding of the evolutionary history of the Cenozoic. This is because the deposits of this era are more accessible than the Mesozoic and Paleozoic ones.

To this we must add that mammal fossils are easier to identify. Their teeth are clearly differentiated into different types. The chewing parts that are the premolars and molars are different with each of the orders of mammals. A single chewing tooth allows you to identify which genus a fossil came from.

Bird diversification

At the beginning of the Paleogene, the first members of living orders and families of owls, hawks, ducks, penguins and vultures evolved.

Currently there is a great variety of birds depending on size and adaptations. But its basic structure has not changed much since the beginning of the Paleogene. This uniformity is not surprising, if we take into account that most birds fly and that the adaptations they obtained for this limit their structure.

Birds adapted to numerous habitats and increased their diversity. One of the first notable adaptations of birds was the development of large flightless predators.

An example of this was the Diatryma which was 2 m tall. It was characterized by having a huge head and beak, short, massive legs, large clawed fingers, and small vestigial wings.

The real success story among birds belongs to the fliers. A wide variety of adaptive types emerged during the Cenozoic era, making them as successful as mammals.

Development of large grasslands

Initially, scientists claimed that grasslands appeared in the Paleogene period, given that the first and only grass fossils were about 55 million years old.

In 2005, a study showed that different varieties of grasses had been digested by dinosaurs between 71 and 65 million years BC. This was confirmed by the analysis of fossilized dung, where they found microscopic silica particles known as phytoliths.

In this way it was demonstrated that at least 5 grass taxa existed during the end of the Cretaceous.

However, as part of the continuing evolution of flowering plants, grasses continued to develop during the Paleogene. With new growth originating near the root, rather than the tip of the plant, grasses presented protection from grazing and fire. Unlike trees, they regenerate quickly and provide renewable food sources for herbivores.

Grasslands developed in areas devastated by fire that could be started by lightning strikes. Animals quickly evolved to make use of this new habitat. This diversified grazing mammals such as antelope, sheep, cows, deer, horses and rhinos.

How is the Paleogene period divided?

The Paleogene period is composed of three phases or epochs that are known as:

Paleocene Eocene Oligocene

Each one has its own characteristics, as described below.

Paleocene Epoch – From 65 to 54 million years BC

This is the initial period of the Paleogene and the Cenozoic Era. After the loss of the giant reptiles that had dominated the Mesozoic, small mammals and birds got the window they needed to multiply and diversify. This was also supported by the existence of dense forests that emerged after the extinction event.

The fauna did not reach a large size, at least at the beginning. Most of these species were no larger than a small pony. Ferns were abundant but gradually flowering plants and conifers began to predominate.

Deciduous trees multiplied in the swamp forests of North America, especially from the mid-latitudes to the Arctic. Grasses that had emerged in the previous period continued to grow in the Paleogene. Nine million years after the extinction period, herbivorous insects emerged that adapted perfectly to the changes.

Reptiles disappeared from the oceans, except for turtles and crocodiles. Sharks and teleost fish thrived, reaching the same level of dominance they have today. Bivalves, echinoids and foraminifera achieved their modern forms.

Finally, as a result of geological events, India collided with Asia, so there was a rapid increase in temperature at the end of this era.

Eocene Epoch – From 54 to 38 million years BC

It happened after the Paleocene and before the Oligocene. It began with extreme global warming in what were the warmest five million years of this entire era. It is possible that this was caused by a large release of methane from the ocean floor.

This led to the growth of trees in the polar regions, while subtropical or tropical angiosperm forests covered most of the territory today known as the United States.

Palm trees grew in Alaska and on Spitzbergen Island, and crocodiles lived in the Arctic Circle. Many new kinds of grasses also evolved, but grasslands had not yet developed. Therefore herbivorous mammals were browsers, and fed on leaves and grasses.

The first mammals with odd toes called perissodactyls (this is the case of rhinos and horses) and the first ones with even toes that are known as artiodactyls (camels) appeared at the beginning of this era.

On the other hand, the first marine mammals were whales in the seas. Primates also appeared. There were also large mammals but they disappeared at the end of the era.

Carnivores include the dog, weasel, bear, and cat families. Most modern orders of birds appeared at this time. Then Africa was an island continent. The climate began the long cooling trend, which would continue through the Cenozoic until the mid-Eocene.

Grasslands had not yet spread in the middle Eocene. Furthermore, North America was dominated by forests and forest mammals. Some of the species from this time included the odd-toed perissodactyls such as the Palaeosyopsthe primitive rodent known as Ischyromtomysand the primate Smilodectes.

We must not leave aside the primitive tapirs or Helatatesto the perridodactyls, Patreofelis, MachaeroidsEchmatemy, Sinopas, artiodactyls, Homacodon and Helohyus among others.

Oligocene Epoch – From 38 to 24 million years BC

This era occurred after the Eocene and before the Neogene period. He distinguished himself by perpetuating the global cooling that would lead to the ice age in the future. The forests began to diminish, while the grasslands expanded at their expense.

The first anthropoid apes also appeared. The newly opened landscapes favored the evolution of prey species and fast predators. Oredodonts multiplied in North America, along with three-toed horses and a variety of rhinoceroses.

The giant Indricotherium which was a type of rhinoceros the size of a medium saruopod appeared in Central Asia. Anthropoid monkeys emerged during this time.

South America was isolated for a few million years. That is why it developed a different fauna and flora in terms of giant carnivorous birds and predatory marsupials.

Cats and dogs were represented among carnivores, such as saber-toothed tigers. In the ocean both seals and sea lions also appeared. The two orders of whales living today, the toothed and baleen whales evolved.

Invertebrates preserved their most modern characteristics. For their part, coral reefs extended in the southern hemisphere to New Zealand. Added to this is the separation of Antarctica from South America, which promoted the formation of an insulating circum-Antarctic current and a permanent ice sheet, which occurred worldwide.

In the Oligocene, the Brontotherium, which was one of the largest land animals that ever lived in North America. Added to this are…