The Ordovician period is the second period of the Phanerozoic and Paleozoic era in the earth's geological time. It appeared 490 million years ago and lasted only 0.01 billion years before ending. According to scientists, the Ordovician Period is divided into three periods, namely the Early Ordovician, the Middle Ordovician and the Late Ordovician. These three periods are the most serious periods of transgression (the geological phenomenon of seawater intruding into continental areas.) It can be said that the earth in the Ordovician period was a big greenhouse, and marine invertebrate animals further flourished, and also derived There are many terrifying creatures. The following ranking list will take you to see the creatures of the Ordovician period, tell you what creatures there were in the Ordovician, what were the giant creatures of the Ordovician? and the reasons for the mass extinction of organisms in the Ordovician. The ten most terrifying creatures of the Ordovician period

1. Eurypterus horseshoe crab

Eurypterus horseshoe crab was born in the Ordovician period, about 460 million to 445 million years ago. Also known as the order Elasmopoda and Euryptera, commonly known as eurypteran horseshoe crabs, plate-footed horseshoe crabs, and sea scorpions, it is an arthropod phylum Limostome that flourished in the Silurian period and became extinct in the Permian-Triassic period. event. It has survived for approximately 250 million years.

Some species of this type of animal were quite large, up to 2.35-2.55 meters long, and were among the largest creatures at that time. However, most species are around 20 cm.

They live near estuaries and deltas. They are terrible carnivores and social animals. Some species have two huge pincers on their heads, which are the evolution of their second pair of legs. It is used to attack the target. Its sharp claws can catch a slippery fish. And their whole bodies are covered with thick armor formed by exoskeletons to protect their bodies.

Horseshoe crab has a pair of compound eyes and a pair of small so-called single eyes. The third and fourth pairs of legs are used for walking, and the fifth pair of legs is used for swimming.

Due to the continuous evolution of the legs of horseshoe crabs, which have become very thick during evolution, some species have the ability to move on land. Fossil research shows that some of these species have evolved a second set of gills in addition to their original gills, which are used to breathe oxygen in the air, thus enabling them to land on land and live amphibiously. Horseshoe crabs once lived in large numbers in what is now New York State in the United States. In 1984, the horseshoe crab of the genus Eurypteryx was selected as the official specimen of New York State.

2. Nautilus

During the Ordovician period, although many types of sea scorpions appeared in the sea and were likely to dominate the ocean, there was one species that originally crawled slowly on the seabed. The original snails (Plectronoceras) formed partitions in their cone-shaped shells so that they could enclose the air and allow the bulky snail shells to float. Moreover, there were body tubes connected between the partitions, and by adjusting the inner space of the partitions, The ratio of gas to liquid controls the amount of buoyancy. When they no longer need to bear their weight, they only need to shrink their bodies and plug the seawater into the gap between the body and the living room. The squeezed seawater can only be sprayed out from the narrow funnel tube. In this way, it can not only generate jet propulsion , you can also control the direction of movement by rotating the funnel tube.

With such sophisticated equipment like submarines and jets, nautiloids became the fastest killer predators in the Silurian period and the most terrifying killer predators among the top ten terrifying creatures in the Ordovician. Every other animal in the ocean moves much more sluggishly, making them easy prey for voracious predators like nautiloids. Nautilus species radiated and evolved various shell shapes during the Paleozoic Era, including straight, arcuate, rolled, and rolled first and then straight. Some orthogonal stones are as big as a small truck, which is amazing.

Recently, some scholars have begun to notice that by observing the growth patterns on the nautilus shell, we can see the period of the moon orbiting the earth, just like the growth rings of trees. Because the nautilus has an evolutionary history of more than 400 million years, the number of days it takes for the moon to orbit the earth in different periods can be inferred by comparing the growth patterns on the shells of nautilus fossils from various ages. It was found that the number of days the moon takes to orbit the earth is gradually increasing, which means that the moon is gradually moving away from the earth. Astronomers from the United States and France also found that the moon has moved away by about 1 meter in the past 28 years. Through observation: there are 30 growth lines on the shell of the living species of nautilus, 26 growth lines on the shell of the Cenozoic Oligocene nautilus, 22 in the Cretaceous of the Mesozoic, and 18 in the Jurassic. There are 15 in the Paleozoic and Carboniferous periods, and 9 in the Ordovician. Therefore, during the Ordovician Period of the Paleozoic Era 420 million years ago, the moon only took 9 days to orbit the earth. It is speculated that the distance between the moon and the earth at that time was only 43% of the current distance. Incidentally, at that time, the earth rotated once, which was one day. Only 21 hours. The rhythmic growth of the nautilus shell provides extremely important clues and evidence for the study of ancient astronomy.

3. Ordovician trilobites

There were more than 500 species of trilobites living in the Ordovician ocean. Trilobites are very well-known fossil animals, perhaps second only to the dinosaurs. Trilobites are the most diverse of all fossil animals. Although there are not as many species in the Ordovician period as there were in the Cambrian period, their number is still huge. This is one reason why trilobite fossils are so common today.

Although trilobites only have armor on their backs, their exoskeletons are still quite heavy. Their exoskeletons are composed of chitin-based proteins combined with minerals such as calcite and calcium phosphide. Unlike other arthropods, which are able to reabsorb most of the minerals in their exoskeleton before molting, trilobites discard all the minerals in their armor during molt, so one trilobite can leave behind multiple well-mineralized shells. exoskeleton, which increases the number of trilobite fossils. During molting, the exoskeleton first separates between the head and thorax. This is why many trilobite fossils are either missing a head or a thorax. In fact, many fossils are the shed skin of trilobites, not dead trilobites. formed by insects. Most trilobites have two facial sutures on their heads to simplify the molting process. There is a pair of compound eyes on both sides of the head, and some species have quite advanced compound eyes.

4. Ringo

Ringo is a type of echinoderm that became extinct in the late Devonian period. It is the oldest class of echinoderms with the simplest skeletal structure.

They are spherical in shape, similar to apples, hence the name (Ringo is the ancient name for apple). They are strikingly similar to crinoids in that they are attached to the base using stem segments and have an expanded shell composed of many different bony plates. It has a calyx and a wrist, and there are as many as 13 to 200 bone plates in the calyx (calyx plate). The calyx plate has plate holes, and the groove and hole system is complex.

Ringo have no real limbs, so they use short, unbranched arms called gills to filter food from the water. In addition, their bony plates have a unique hole structure for breathing. There are about 100 genera in the class Cylinthora, which began to appear in the Ordovician period and died out in the Devonian period.

5. Graptolite

Graptolite first appeared in the Middle Cambrian and flourished in large numbers in the Ordovician. It mainly operated by floating method, was widely distributed, evolved quickly, and was easy to preserve. Important zoning fossils from the Pottery Period. In the early part of the Early Ordovician, dendritic graptolite was dominant. In the middle period, axonate suborders of orthograptolites flourished in large numbers. In the late period, graptolites with axis suborders appeared. The middle and late Ordovician were the heyday of orthograptolites. . There are many graptolite fossils in the Silurian period, among which graptolite fossils are the main ones, such as graptolite, graptolite, saw graptolite, rake graptolite, etc. During the Devonian, most of the orthograptolites became extinct, leaving only a small number of monograptolites and dendrobites. Graptolites finally became extinct in the late Carboniferous.

6. Bryozoa

There are nearly 4,000 species currently living. From the Ordovician to modern times, there are about 15,000 fossil species. Allegedly responsible for the extinction of trilobites.

Biologists say the reason for the extinction of trilobites is this: with the rise of carnivorous creatures such as nautiloids, horseshoe crabs and fish, weak trilobites became the targets of devouring. Coupled with changes in the marine environment, trilobites became extinct, but there is no reliable evidence to confirm this statement.

Bryozoa appeared in the Ordovician, and bryozoans gradually emerged in the ocean, while trilobites gradually declined. This rise and fall made it easy for people to connect the extinction of trilobites with the rise of bryozoans. Recently, many parasitic bryozoans were found on the Ordovician trilobite specimens we collected, and pathological changes were obvious in the parasitic parts.

Some people may wonder why it is possible that bryozoans are parasitic on the surface of a trilobite, leading to its death? Crustaceans in modern oceans are often parasitized by such and such organisms. They all live together harmoniously. What's more, can the cold fossils prove that bryozoans are attached to living trilobites? They may be fixed to the trilobite carapace scattered after death.

7. Starfish

Starfish (echinoderms) The marine creatures of the Ordovician period are the earliest ancestors of modern animals. At that time, corals and ancient starfish called starfish grew on the ocean floor. They are also representatives of organisms that have survived from the Ordovician period to the present.

8. Armored fish

Armored fish are the ancestors of existing cyclostomes, such as lampreys. They first appeared in the Ordovician period and became extinct at the end of the Devonian period. It looks like a fish, and the armored fish head and the outside of the body are covered with bone plates. The mouth has no upper and lower jaws, a bony central axis and no real fins. It is different from fish, but similar to the living Cylostomia.

9. Fengjiao Kunmingfish

There is currently only one species of fish in the genus, Fengjiao Kunmingfish. It is also the oldest known vertebrate and the earliest fossil discovered by scientists. It was discovered in strata of the Cambrian Period 530 million years ago. It appears to have a skull and bones made of cartilage.

10. stromatoporoids

stromatoporoids are an extinct group of marine organisms. They are named after the layered surface of their vaginal bones. They appeared in the late Ordovician period and became completely extinct in the Cretaceous period.

There are almost all their representatives in the Silurian and Devonian carbonate sedimentary strata around the world. Quasi-radioactive stroma and other species were found in the Jurassic of Mount Everest in China. In Japan, it is mostly found on the Jurassic Bird's Nest limestone.

They are all marine, living in colonies, growing on the bottom of the sea or attached to other objects.

They usually live in shallow seas that are clear and warm, with moderate salinity, sufficient sunshine, and strong hydrodynamic force. Some also live in deeper waters in front of lagoons or reefs. Often form biological reefs with corals and algae.

In fact, in general, according to the current fossil data, among the ten most terrifying creatures of the Ordovician, the most terrifying ones should belong to the eurypteran horseshoe crab and the nautilus. More creatures still need to be explored and discovered by scientists. If the latest Ordovician horror creatures are discovered, this article will be updated as soon as possible. The reasons for the mass extinction of organisms in the Ordovician period. The Ordovician period was far more than the top ten recorded horrific creatures. There were also many echinoderms, arthropods, molluscs, etc. Compared to the Cambrian, the organisms in the Ordovician were more developed. Prosperous, but this period of such prosperous life also encountered the first mass extinction of species on the earth. The number of biological taxa during the Ordovician mass extinction was rated as the second among the five mass extinctions in the history of the earth.

The Ordovician mass extinction included the extinction of about 85% of species, 27% of families and 57% of genera. Scientists speculate that the main cause of this extinction was the entry of Gondwana into the Antarctic region. , affecting changes in global circulation, causing global cooling to enter the Andean-Saharan Ice Age, and sea levels to drop significantly.

Not only that, there were also three large-scale 8-level volcanic eruptions in the Ordovician, which was also the main reason. However, these are scientists' speculations and cannot be confirmed with their own eyes. Another more accepted theory is that a star 6,000 light-years away exploded and gamma rays hit the earth, causing the ozone layer to be destroyed, directly killing the Ordovician period. most organisms.