The Triassic Period marks the beginning of the Mesozoic Era and the end of the Paleozoic Era. This period is the first of the three that make up this Age, beginning approximately 252 million years ago and ending 200 million years ago.
This period is characterized by the rise of a group of diapsid reptiles that later became very important: the dinosaurs.
We can subdivide the Triassic into:
- Lower Triassic. It begins 252 million years ago and ends 247 million years ago. The period after the great extinction of the Permian, it is characterized by a recovery of the terrestrial fauna and flora.
- Middle Triassic. It begins 247 million years ago and ends 235 million years ago. The Tethys Sea appears, giving Pangaea its characteristic C shape.
- Upper Triassic. It begins 235 million years ago and ends 200 million years ago. An almost total separation of the supercontinent Pangea is observed.
The Triassic Period begins after the great Permian extinction (last Paleozoic period). This extinction swept away more than 99% of life on Earth, leaving the planet almost without animals or plants. Earth was plunged into chaos by major eruptions and earthquakes, destroying almost everything that was there.
At the beginning of the Triassic, the emerged land was made up of a single continent: Pangaea. This C-shaped supercontinent was surrounded by a single ocean known as Tethys, which begins to separate the supercontinent into 2: Laurasia and Gondwana.
The climate was very warm, with high but milder temperatures as we moved away from Ecuador, but there was no ice at the poles (the only ice that existed was in the mountain ranges). On the coasts, the warm climate was milder, and as we approached the poles we found wetter climates and forests, while the central part of Pangea was characterized by a very dry arid climate.
As we approach the end of the Triassic Period, the supercontinent Pangea suffers from the action of tectonic plates and begins to separate into two. At the end of the Triassic, it is already separated into two major continents: northern Laurasia and southern Gondwana. This is the organization that the continents will have during the Jurassic.
In the Paleozoic Era (before the Triassic), the first thing that colonized the mainland was plants. Great ferns and later gymnosperms.
Angiosperms have not yet appeared. That after a great extinction that destroyed practically everything on Earth, it is easy to explain how the animals could survive and later radiate in different ancestors due to their ability to move and therefore escape from danger, but the plants are static and there were studies on how they could survive such extreme conditions.
In reality, the plant itself was not what survived, but a tiny part of it: the seed.
There are a number of seeds that can survive extreme temperatures and very adverse conditions (such as floods or fires that last for days) and then sprout or even some that need that adverse condition to remove competition to sprout.
These are the types of plants that usually appear wild after a forest fire, and are thought to be the characteristics that allowed the Earth to repopulate with forests.
After the great extinction of the Permian, many niches were left free and to colonize again, so the plants were the first to fill them again.
There was no major change in the number of species of gymnosperms or ferns, but the number of individuals increased mainly in coastal (ferns and palms) and inland (conifers) areas. The only place where gymnosperms did not have a large population was in the central desert.
The boom in the number of plant populations allowed the climate to be humid and gradually softened the aridity for the entry into the Jurassic.
After a mass extinction, there are a large number of niches that remain empty and therefore all living beings try to occupy those that can, which forces some of them to change and evolve.
The terrestrial fauna that survived the great Permian extinction consisted of both invertebrates (although their size was reduced to what we know today, and did not undergo a great evolutionary change with respect to previous times) and vertebrates of which reptiles and what are known as mamipheroids-reptiles (therapsids) stood out.
At the beginning of the Triassic, the most predominant fauna was that of terapids, with famous specimens belonging to the group of cynodonts such as the Thrinaxodon.
The cynodonts were a series of medium-sized therapies that already presented very mammalian structures such as the presence of a zygomatic arcade (unique in mammals).
Some authors argue that these mammy-reptiles already had hair or primitive mammary glands, but the soft structures are difficult to preserve in fossil form. What has been preserved are a series of hairs called “vibrisas”, commonly known as “the whiskers”, a series of sensory hairs that give the animal extra knowledge of the surrounding environment.
The vibrisa is a white but keratinized structure, something that allowed its preservation but has been found in a few specimens (that’s why it is assumed that only some of them had it, it has not been generalized).
In the group of reptiles, we can already distinguish two groups: Lepidosauromorpha and Archosauromorpha.
Within Lepidosauromorpha there are extinct groups such as the Sauropterygios, among which are marine reptiles such as the Mosasaurus, and those properly called Lepidosaurus which are modern reptiles, which have survived to the present day and where snakes, lizards, and varans appear among others.
Archosauromorpha’s group includes reptiles with much more prehistoric and archaic features, such as pteranodons, crocodiles, and dinosaurs (and with them also birds, but the first prehistoric bird originated several million years later).
Thus, Archosauromorpha is one of the most incredible evolutions and changes in a series of animals that dominated the Earth for almost 200 million years.
Del Triasico is an animal that we have already mentioned several times in the blog, known as Euparkerya and which we can call “the ancestor of the dinosaurs”, and introduced great changes in the group of archosaur reptiles that allowed them to take advantage of other animals to dominate the Earth.