What kind of evolutionary history did the "leader" of the Paleozoic Era experience?

When it comes to paleontology, many people may think of dinosaurs first. Dinosaurs are the most eye-catching animal group in the Mesozoic Era and can be regarded as the leaders of the animal kingdom at that time. The leader of the Paleozoic Era is none other than trilobites.

Saying that they are the leaders does not mean how powerful they are, but refers to their diversity. So far, the trilobite fossils discovered by humans, both in terms of variety and quantity, far exceed those of other species. It is no exaggeration to say that they exceed the sum of all other species of the same period.

Although many people have heard of the name trilobite, not everyone knows the origin of this name. In fact, this name is a direct translation of the English word "Trilobite". "Tri" means three, and "lob" comes from "lobe". Because their bodies can be divided into three parts from the horizontal direction: the central axis, left lobe and right lobe, and from the vertical direction, they can be divided into three parts: head segment, thorax segment and tail segment. However, compared with insects, which are also arthropods, there are still many differences. The legs of insects are concentrated in the thorax, while the legs of trilobites are scattered in various parts of the body.

In addition, the stomach, intestines and other major internal organs of trilobites are concentrated in the head, and they mainly feed on organic matter on the seabed. In addition, the body is covered with a hard exoskeleton, and there are small thin legs without much meat, which makes them neither taste good nor nutritious. But as the saying goes, "grasshoppers are also meat", not to mention that there is such a large population to support them, predators will naturally not let them go, but they still have some choices, usually only eating the head that is relatively nutritious and not so difficult to chew. This is one of the reasons why many trilobite fossils do not have heads. Another reason is that many fossils are shed empty shells. By the way, in addition to a genus that is formally called bat insects, in ancient my country, headless trilobite fossils were also called bat insects or bat stones, because the trilobite with only the tail carapace left looked like a bat with wings spread.

In order to resist natural enemies and adapt to the environment, trilobites did not only focus on armor. In the Cambrian period, trilobites represented by Ledlicki were generally characterized by a flat body, ribs extending from the chest to both sides, a small tail, and spines extending from the central axis. In the Ordovician period, they were in their heyday with rich forms, heads and tails tending to be equal in size, and bodies became more three-dimensional. Among them were the largest Tyrannosaurus, the Kavalerski comb worms with long eyestalks like snails, and the mirror-eyed worms with well-developed compound eyes and good at swimming.

After experiencing the Ordovician extinction event, only a few species of trilobites remained in the Silurian period. However, in the Devonian period, they let themselves go, showing richer and more exaggerated shapes than those in the Ordovician period, such as the three-horned trilobite with long spines and a trident on its head. Many trilobite enthusiasts got into the hobby from the trilobites of this era. On the one hand, this exaggerated shape was used to show off to the opposite sex, and on the other hand, it was because in the Devonian period, fish had a weapon that could easily break through defense - the jaw.

After the Devonian period, trilobites were basically in a state of lingering, but they still persisted for 150 million years before they bid farewell to this world completely. Such a record is not achieved simply by stacking armor, but is the result of extensive adaptability.

Although trilobites never reached the top of the food chain even in their prime, their existence time makes the dinosaurs, which ruled the earth for about 150 million years, feel ashamed, not to mention us humans who have only a few million years of history. In this sense, perhaps calling them the leaders of the Paleozoic Era is a bit conservative. They are the real leaders of the paleontological world.