CAMBRIAN: CHARACTERISTICS, SUBDIVISIONS, FLORA, FAUNA AND CLIMATE - GEOGRAFÍA - 2024

The Cambrian is the first period that makes up the Paleozoic Era. It spanned from 541 million years ago to 485 million years ago. During this geological period, the Earth witnessed the greatest diversification and massification of existing life forms.

In the Cambrian, the so-called “Cambrian Explosion” occurred, in which a large number of multicellular animal species appeared that mainly populated the seas. In this period chordates made their appearance, a phylum to which amphibians, reptiles, birds, mammals and fish belong.

Trilobite fossil. Source: Pixabay.com

The Cambrian period has been one of the geological eras most studied by specialists. They have evaluated the geological changes that occurred during the period, the evolution of existing living organisms, as well as the environmental conditions that existed at that time.

However, there are many aspects that remain to be clarified with the study of the various fossils that are still being recovered today.

General characteristics

Duration

The Cambrian period lasted 56 million years. It was a momentous period, full of significant changes.

Amplification of life forms

One of the main characteristics of the Cambrian period was the great diversification and evolution of living beings that at that time populated the planet. In the Cambrian a large number of species and phyla appeared that have even remained until today.

Divisions

The Cambrian period was divided into four epochs or series: Terreneuvian, Epoch 2, Miaolingian and Furongian.

geology

During the Cambrian, the most significant geological changes had to do with the fragmentation and reorganization of supercontinents and their fragments.

Most specialists agree that the continents or fragments of the earth's crust that were found in the Cambrian were the result of the fragmentation of a supercontinent known as Pannotia.

As a product of the fragmentation of Pannotia, four continents were formed: Gondwana, Baltica, Laurentia and Siberia.

Apparently, the speed of continental drift was high, causing these fragments to separate from each other relatively quickly. This is how Gondwana moved towards the south pole, while the other four were located at the north pole of the planet.

It is important to mention that the displacement of these fragments of the earth's crust led to the formation of new oceans in the space that separated them, namely:

• Lapetus: separated Baltica and Laurentia.
• Proto - Tethys: separated the three continents of northern Gondwana
• Khanty: located between the Baltics and Siberia

Similarly, the northern half of the planet almost entirely was covered by the Phantalassa Ocean.

It is believed that during the Cambrian the surface of the continents was attacked by an important erosive process, in such a way that the panorama of these was rather that of an extensive plain.

Weather

Few records are had of the climate during the Cambrian. There are really few fossils that allow us to study the environmental characteristics of this period.

However, it can be said that the climate during the Cambrian was much warmer than that of other geological periods. This is because there were no large ice chips on the planet.

Likewise, since almost the entire northern hemisphere was occupied by the immense Phantalassa ocean, many affirm that the climate was temperate and oceanic.

Similarly, scholars agree that, in terms of climate, there were no seasonal fluctuations. In such a way that it can be affirmed that, at least during the Cambrian, the climate was quite stable without sudden changes in temperature.

However, at the end of the Cambrian there was a drop in temperature, which caused certain parts of the continents that were slowly moving, to be covered by ice. This brought negative consequences for the living beings that inhabited the planet.

Therefore, it can be said that the Cambrian climate was warm and stable for most of the time, which allowed life to develop over time, in what many still call "The Great Cambrian Explosion".

Lifetime

While it is true that life appeared in the Archaic eon, the life forms that existed when the Paleozoic era began, specifically the Cambrian period, were very simple. They were only limited to very simple living beings, both unicellular and multicellular, generally soft-bodied.

During the Cambrian period an unusual diversification of life forms occurred. The specialists called this process "The Cambrian Explosion".

The Cambrian Explosion is a phenomenon that even today draws the attention of most specialists who have devoted themselves to studying geological eras.

This is because, in theory, a great diversity of living things appeared almost simultaneously. All this according to the fossil records that have been recovered from this period.

Among the main doubts that have arisen among specialists, two main ones can be mentioned:

• How is it possible that life forms belonging to different evolutionary pathways arose almost at the same time?
• Why did these new forms of life appear on Earth so abruptly and suddenly, without evidence of their ancestors?

-Reasons for the Cambrian Explosion

Until today, specialists have not been able to establish specifically what were the reasons why life diversified so widely during the Cambrian period. However, there are some conjectures that seek to answer this question.

Environmental transformation

During the Cambrian period, the Earth underwent a series of changes and transformations at the environmental level that allowed it to become more habitable. These changes include:

• Increase in atmospheric oxygen.
• Consolidation of the ozone layer.
• Sea level rise, increasing the possibilities for more habitats and ecological niches.

Tectonic movement

There are specialists who suggest that during the Cambrian period a significant tectonic phenomenon must have occurred, or as they call it, “of great magnitude”, which caused the sea level to rise, even expanding over some surfaces of the existing continents..

This hypothesis has been very receptive in the community of geologists, since it is known that during this period tectonic activity was frequent.

Changes in animal morphology

During this period it was observed that existing animals developed a series of modifications in their body structure, which allowed them to adapt to the environment and adopt new behaviors such as in the food field.

During this period the articulated limbs and the compound eye appeared, among others.

Flora

The representatives of the plantae kingdom that existed during the Cambrian period were quite simple. Mainly there were some organisms capable of carrying out the photosynthesis process.

These were unicellular, that is, they were made up of a single cell. These include some types of blue-green algae and other types of organisms that appeared later.

The latter were calcareous in appearance and were deposited on the seabed, forming small heaps. But not all of them had this configuration, there were some that were grouped together forming small sheets that as a whole were known as oncoids.

Algae were found in the seas, while on the earth's surface the only specimens of plants were some lichens, which are very simple forms of plants.

Similarly, there is evidence of the existence of another species of organisms of the plantae kingdom, the acritarchs. These were living beings of which there is an abundant fossil record.

Specialists have established that acritarchs were part of phytoplankton, which is why they have traditionally been considered plants. However, there are others who consider that acritarchs are a phase or stage in the development of some organism of the animal kingdom.

Despite this, it has been possible to collect abundant fossils of these organisms, although they have not been studied in depth, because their microscopic size has made the work of specialists difficult.

Fauna

Animals found in the Cambrian period lived mainly in water. They lived in the vast oceans that covered the planet.

Most of the animals that inhabited the Cambrian were complex invertebrates. Among the greatest exponents of this group are: trilobites, some large invertebrates and other groups such as mollusks, sponges and worms.

Sponges

During the Cambrian period, it was common for a large number of sponges to be found on the seabed, classified today within the phylum porífera.

These are characterized by having pores throughout their body structure. The water circulates through these, which allows them to filter and retain the small food particles that are suspended in it.

Thanks to the fossil records, information has been obtained on how those first sponges might have been. According to these, there were tree-like sponges and others with a cone shape.

Arthropods

Arthropods have always been a very large group of animals. Today it is the most abundant phylum in the animal kingdom. In the Cambrian this was no exception, as there were a large number of animals belonging to this phylum.

Within this group, the most representative were the trilobites. These were a group of arthropods that abounded during this period and were maintained until almost the end of the Permian period.

The name Trilobites comes from its anatomical configuration, since its body was divided into three parts or lobes: axial or spinal, left pleural and right pleural. It was also one of the first animals to develop the sense of sight.

Mollusks

This phylum underwent a great transformation, diversifying into several classes, some of which are still found today.

These include: gastropod, cephalopod, polyplacophora and monoplacophora, among others. It is known, thanks to the fossil records, that there were also other classes of mollusks that are extinct: Stenothecoida, Hyolitha and Rastroconchia.

Echinoderms

It is a phylum of animals that had a great expansion and diversification during the Cambrian period. During this period, new species of echinoderms appeared that could adapt to the different environmental conditions that existed.

However, only one class survived in time and has remained to this day, the crinoid class.

Chordates

This was perhaps the most important group of animals that had its origin in the Cambrian period, since from them a large number of animal groups have diversified such as vertebrates (amphibians, fish, reptiles, birds, mammals), the urochordates and cephalochordates.

The distinctive feature of chordates is that they have a structure known as the notochord. This is nothing more than a tubular cord that extends throughout the entire dorsal part of the individual and has a structural function.

Likewise, among other characteristics of chordates, we can mention the presence of a central nervous system, a post-anal tail and a perforated pharynx.

Anomalocaris. Source: Yinan Chen, via Wikimedia Commons

Likewise, in the seas there were some predators that fed on the rest of the smaller organisms. Among these we can mention the Anomalocaris, which was the largest known predator during the Cambrian period.

This was an animal related to the arthropod phylum. It had long arms covered with extensions like thorns, which served to bring food closer to its mouth, several rows of teeth that served to grind and process food, in addition to having compound eyes, which allowed it to perceive the slightest movement close to him.

As for the size, it could reach up to 1 meter in length. It was the biggest predator of the time. So much so that it was at the top of the food chain.

Subdivisions

The Cambrian period is divided into several epochs: Terreneuvian, Epoch 2, Miaolingian and Furongian.

Terreneuviense

It was the oldest time of the Cambrian period. It had its beginnings 541 million years ago. Its beginning was marked by the appearance of fossil specimens of an organism known as Trichophycus pedum and its end was determined by the appearance of trilobites.

During this time the diversity of living beings was still scarce, since it was in the following subdivisions in which it was expanded.

Epoch 2

It began about 521 million years ago. Its beginning was determined by the appearance of the first trilobite fossils.

Specialists have established that the end of this era was determined by the extinction of a large number of animal specimens. This was due to a variation in environmental conditions, which prevented some species from surviving.

Miaolingian

It was only named after it in 2018. It is the third and penultimate period of the Cambrian. It began approximately 509 million years ago. During this time the trilobites began to increase in number and diversify.

Furongian

It began 497 million years ago. Its beginning was marked by the appearance of a new species of trilobites, the Glyptagnostus reticulatus and its end by the appearance of a type of marine chordate animal known as the conodonto.

References

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