MESOZOIC ERA: CHARACTERISTICS, DIVISIONS, GEOLOGY, SPECIES - GEOGRAFÍA - 2024

The Mesozoic Era was the second era of the Phanerozoic Aeon. It began approximately 542 million years ago and ended 66 million years ago. It has been studied in depth by paleontologists, since it was in this era that the best known animals of antiquity lived: dinosaurs.

Likewise, this era holds a mystery, the causes of which specialists have not yet been able to unravel: the mass extinction of the dinosaurs. During the Mesozoic Era, the planet became more habitable, both for plants and animals, even having characteristics similar to those it has today.

Representation of a scene from the Mesozoic Era. Source: Gerhard Boeggemann, via Wikimedia Commons

General characteristics

Duration

The Mesozoic Era lasted approximately 185 million years distributed in three periods.

Intense tectonic activity

During this era the tectonic plates were very active. So much so that the supercontinent Pangea began to separate and form the different continents that are known today. Because of this, the current oceans were formed.

Dinosaurs

Dinosaurs appeared and diversified, which had hegemony throughout the time that the era lasted. Here appeared the large herbivorous dinosaurs and fearsome predators such as the Tyrannosaurus rex and the velociraptor. The dinosaurs dominated both the land and the water and the air.

Mass extinction process

At the end of the last period of the Mesozoic Era, a mass extinction process took place in which the dinosaurs disappeared.

According to specialists, the causes of this could have been several. The two most likely causes were the fall of a meteorite on the site where the Yucatan Peninsula is today and the intense volcanic activity.

There are many who believe that both things could happen simultaneously. What is certain is that the climatic conditions of the planet changed significantly at the end of the Cretaceous period, which caused that very few species of living beings that existed could adapt.

Divisions

The Mesozoic Era was found divided into three periods: Triassic, Jurassic, and Cretaceous.

Triassic

It was the first division of the era. It lasted approximately 50 million years. In turn, it was divided into three eras: early, middle and late Triassic. Here the first dinosaurs appeared and the earth's surface was forming a single mass known as Pangea.

Jurassic

The second division of the era became known as the age of the dinosaurs. It lasted approximately 56 million years. It was divided into three epochs: early, middle and late. Here the great dinosaurs appeared and at the geological level the separation of the Pangea began.

Cretaceous

Last period of the Mesozoic Era. It spanned approximately 79 million years, divided into two epochs: Lower Cretaceous and Upper Cretaceous.

It was the time when large land predators such as the famous Tyrannosaurus rex existed. Likewise, the separation of the Pangea continued here. It culminated in the planet's best-known mass extinction process, in which dinosaurs became extinct.

geology

During the Mesozoic Era there were a lot of changes at the geological level. The activity of the tectonic plates was very intense, which caused the collision and separation of some of them. This in turn caused a rearrangement of the water masses that existed at that time.

Tectonic activity

At the beginning of the Mesozoic Era, all the supercontinents that had existed in later eras were forming a single land mass, which specialists called Pangea. Despite being a united mass, in the Pangea two well-differentiated areas were distinguished:

• Laurasia: it was located in the north of the Pangea. It contained the territories that today correspond to the European continents and North America.
• Gondwana - As observed during ancient geological eras, it was the largest piece of land. It was made up of the territories that currently correspond to Africa, Australia, South America, India and the Arabian peninsula.

This is how the earth's crust was at the beginning of the era. However, as time progressed and as a result of the friction of the tectonic plates, the supercontinent Pangea began to separate. This separation began during the first period of this era, the Triassic, and was further accentuated during the Jurassic.

Configuration of the planet in the Triassic. Source: User: LennyWikidata, via Wikimedia Commons

As a result of this first fractionation of the Pangea, the two supercontinents mentioned above separated: Gondwana to the south and Laurasia to the north.

The most intense tectonic activity was recorded during the last period of the era, the Cretaceous. It was in this period that Laurasia and Gondwana became separated in such a way that the resulting chunks of land closely resemble the continents that exist today.

Among the changes that the Gondwana supercontinent underwent at the end of the period, the following can be mentioned: South America separated from the African continent, Australia separated from Antarctica and began to move further north, India separated from Madagascar and became moved north, towards the Asian continent.

Orogeny

During this period, from the orogenic point of view, there were no relevant episodes, except perhaps the formation of the Andes mountain range on the South American continent, caused by the tectonic activity of the South American and Nazca plates.

Changes at the level of water bodies

At the beginning of the period, there were only 2 oceans on the planet: the Panthalassa, which was the largest and surrounded the entire Pangea, and the incipient ocean Tethys, which occupied a small gulf at the eastern end of the Pangea.

Later, during the Jurassic period, the first signs of the formation of the Atlantic Ocean were seen. By the end of the era, the Pacific Ocean had already formed, which was what it is today, the largest ocean on the planet. The Indian Ocean also had its genesis in the Mesozoic Era.

At the end of the Mesozoic Era, the planet had a configuration very similar to what it has today, in terms of oceans and land masses.

Volcanic activity

At the end of the Mesozoic Era, intense volcanic activity was recorded, specifically in the Cretaceous period, which was the last.

According to the fossil records and the analysis of specialists, it was in the area known as the Deccan plateau, in India, that this activity took place. There are lava flows from those eruptions.

Likewise, according to the information collected, the magnitude of these volcanic eruptions was such that even the lava in certain places could reach 1 mile thick. It is also estimated that it could have traveled distances as long as 200 thousand square kilometers.

These large-scale eruptions brought catastrophic consequences for the planet, so much so that they are even mentioned as one of the possible causes of the extinction process that occurred at the end of the Cretaceous period and the beginning of the Paleocene (Cenozoic Era).

Emission of gases and other materials

The volcanic activity that occurred in this era caused a large amount of gases, such as carbon dioxide (CO2), to be emitted into the atmosphere, as well as a lot of dust, ash and debris.

This type of material, which was kept in the atmosphere for a long time, is capable of reflecting sunlight. Because of this, the sun's rays could not reach the earth's surface.

This resulted in a considerable decrease in the temperature of the planet, which ceased to have the warmth and humidity that it enjoyed during the Triassic, Jurassic and much of the Cretaceous.

The planet became an inhospitable place that made it very difficult for the species that existed, especially the dinosaurs, to survive.

Weather

The climate during the Mesozoic Era varied in each of the periods that made it up. Despite this, it can be stated that during almost the entirety of the era the climate was warm, with high temperatures.

At the beginning of the Mesozoic Era, the climate in the interior of the Pangea was quite arid and dry. This was so thanks to the immense size of this supercontinent, which caused much of its land to be far from the sea. It is known that in the areas near the sea the climate was somewhat milder than inland.

With the advance of time and the entrance to the Jurassic period, the level of the seas rose, which caused a change in climatic conditions. The climate became humid and warm, which favored the diversification of plants, causing a large number of jungles and forests to develop in the interior of the Pangea during that period.

During the late Cretaceous period the climate continued to be quite warm. So much so that, according to fossil records, the poles were not covered with ice. This indicates that temperatures across the planet must have been more or less uniform.

These conditions remained so until the end of the era. At the end of the Cretaceous period, the planet's temperatures dropped considerably, an average of 10 degrees. Scientists have several hypotheses as to why this happened.

One of these theories states that the intense volcanic activity surrounded the planet with a layer of gases and ash that prevented the penetration of solar rays.

Lifetime

The Mesozoic Era was characterized by several milestones regarding the development of life: in the botanical part, the first angiosperms (flowering plants) appeared, and in the zoological part, the diversification and dominance of dinosaurs.

-Flora

Plant life forms were greatly diversified during the Mesozoic Era. During most of the era, the type of plants that dominated the landscape were ferns, which were quite abundant (especially in humid places), and gymnosperms, which are vascular plants (with conductive vessels: xylem and phloem) and are also seed producers.

At the end of the era, specifically in the Cretaceous period, flowering plants, known as angiosperms, made their appearance.

Angiosperms

They represent the most evolved plants. Today they are the ones with the largest number of species. However, when they appeared in the Cretaceous period, they were found in a much lower proportion than gymnosperms.

The main characteristic of these plants is that their seeds are enclosed in a structure known as an ovary. This allows that seed to develop protected from external agents that can damage it. This simple fact constitutes a huge evolutionary advantage in reference to gymnosperms.

In the Mesozoic Era they were represented by three groups: the conifers, the benettitales and the cycads.

Conifers

These types of plants are characterized by the fact that their seeds are stored in structures known as cones. Most of these are monoecious, that is, they present the male and female reproductive structures in the same individual.

Its trunks are woody and have evergreen leaves. Many of the forests that populated the planet were made up of conifers.

Cicadaceae

This group of plants are characterized by having woody trunks that do not have branches. Its leaves are located at the terminal end and can reach up to 3 meters in length.

They are dioecious plants, which means that there were individuals that possessed female reproductive structures and individuals that possessed male reproductive structures. Its seeds, covered by a material with a fleshy texture, were oval.

Benettitales

They were a group of plants that abounded during the Jurassic period of the Mesozoic Era. They became extinct at the end of the Cretaceous.

Two main genera are identified from this type of plant, the Cycadeoidea and the Williamsonnia. The former were small plants, without ramifications, while the specimens of the genus Williamsonnia were tall (2 meters on average) and did present ramifications. They were plants that closely resembled the cycads, which is why until recently they were considered to belong to this genus.

-Fauna

The fauna of the Mesozoic era was dominated by reptiles, mainly from the Jurassic period, and until the extinction of the late Cretaceous, dinosaurs were the dominant group.

Not only in the terrestrial habitat, but in the marine and the aerial one. Likewise, the first birds and the first placental mammals appeared in the Jurassic.

Aerial vertebrates

The skies of the Mesozoic Era were crossed by a large number of representatives of the reptilian group. They were able to acquire the ability to fly thanks to the fact that they developed a kind of membrane that stretched between the toes of their front or rear limbs.

Pterosaurs

They ruled the skies throughout the Mesozoic Era. They appeared in the Triassic period and became extinct in the mass extinction process of the late Cretaceous.

Its main characteristic was its wings, which were a membrane that extended from the trunk to the fingers. This enabled them to plan first and then learn to fly.

They were oviparous organisms, that is, they reproduced through eggs that developed outside the mother's body. Likewise, contrary to what might be thought, her body was covered with hair.

Its size could vary; They were as small as a sparrow, even very large like the Quetzalcoatlus (whose wings had an approximate wingspan of 15 meters)

In terms of their eating habits, they were carnivores. They fed on other smaller animals, such as insects or even fish.

Terrestrial vertebrates

In terrestrial habitats, the predominant animals were dinosaurs. There were so small that they did not reach the meter of height, until the immense herbivores of the Jurassic. Likewise, some were carnivores, while others fed on plants.

In each of the periods that made up the Mesozoic Era there were characteristic and dominant dinosaurs.

Triassic period

Among the dinosaurs that dominated this period can be mentioned:

• Cynodonts: This group is believed to be the ancestor of modern mammals. Among these, the most representative genus was the Cynognathus. This was small in size, and could reach up to 1 meter in length. It was quadruped, its legs being short. They were carnivores, so their teeth were designed to cut and tear the meat of their prey.
• Dicynodonts: This group of dinosaurs are also related to primitive mammals. Evolutionarily they were connected to the cynodonts. They were solid-bodied, short-boned. Its teeth were small and also had a structure similar to a beak, capable of cutting. Regarding the type of food, they were herbivores.

Jurassic period

During this period the large herbivorous and carnivorous dinosaurs predominated, which have become so famous through dinosaur cartoons and movies. Some of them were:

• Brachiosaurus: It was one of the largest dinosaurs that have ever existed. According to estimates, its weight could be around 35 tons and about 27 meters in length. It was quadruped and had an extremely long neck.
• Stegosaurus: this was a dinosaur whose body was fully armored and protected. Its back was covered by a kind of bony plates for protection and its tail had spikes that could measure up to more than 60 centimeters. They could reach a weight of up to 2 tons and lengths greater than 7 meters. It was also a herbivore.
• Allosaurus: it was one of the great carnivores that inhabited during the Jurassic. According to collected fossils, it could weigh more than 2 tons and reach more than 10 meters in length.

Representation of a stegosaurus. Source: Charles R. Knight

Cretaceous period

The dinosaurs that existed here have also been highly recognized thanks to their appearance in movies and cartoons. Here are a few:

• Ceratopsids: the famous Triceraptops belonged to this group. They were quadrupeds and their main characteristic was the shape of their head, which had a fairly noticeable widening, in addition to the horns it had. It could reach a weight of more than 6 tons.
• Theropods: the dinosaurs belonging to this group were the great predators of the time. The Tyrannosaurus Rex and the Velociraptor belonged to this group. They were bipedal and had very poorly developed upper extremities. Its teeth were extremely sharp, ready to tear the flesh of its prey.

Aquatic vertebrates

Life in the seas was also quite diverse during the Mesozoic Era. During the Triassic there were not as many vertebrates as in the Jurassic or Cretaceous. Here are a few:

• Notosaurus: it was one of the first aquatic reptiles. They were great predators of fish, thanks to the sharp teeth they possessed. It had four limbs and a fairly long neck. It is believed that they could also exist in terrestrial habitats close to the seas.
• Mosasaurs: these were perfectly adapted to marine life. Their limbs were modified to form fins that allowed them to move comfortably through the water. Likewise, they had a dorsal fin. They were fearsome predators.
• Ichthyosaur: it was one of the largest marine animals in terms of size, since it could measure up to 20 meters in length. Among its distinguishing features was its elongated and serrated snout.

Invertebrates

The group of invertebrate animals also experienced some diversification during the Mesozoic Era. Among the phyla that stood out the most, the mollusks can be mentioned, being represented by gastropods, cephalopods and bivalves. There are abundant fossil records of the existence of these.

Likewise, in marine environments the group of echinoderms was also another edge that flourished, especially stars and sea urchins.

On the other hand, arthropods also had their representation in this era. There were some crustaceans, especially crabs, as well as butterflies, grasshoppers, and wasps.

Here it is important to mention that the emergence and development of angiosperm plants was linked to the development of certain arthropods that, as is well known, play an important role in the pollination process.

References

1. Diéguez, C. (2004). Flora and vegetation during the Jurassic and Cretaceous. Cordova Botanical Garden Monograph. 11. 53-62
2. Fastovsky, DE, and Weishampel, DB (1996). The evolution and extinction of the dinosaurs. In The evolution and extinction of the dinosaurs Cambridge University Press.
3. Haines, Tim (2000) Walking with Dinosaurs: A Natural History, New York: Dorling Kindersley Publishing, Inc., p. 65
4. Lane, G. and William A. (1999). Life of the Past. 4th ed. Englewood, NJ: Prentice Hall
5. Stanley, S. (1999). Earth System History. New York: WH Freeman and Company.