The Devonian Period began at 419.2Ma (419 million years ago) and lasted nearly 60 million years, ending at 358.9Ma (358 million years ago), the fourth of the Paleozoic periods of the geological epoch, belonging to the Phanerozoic Paleozoic
The Devonian period is also known as the age of fish, so let's take a look at how fish evolved! fish
Classes are generally divided into five categories: jawless, shieldfish, spiny fish, cartilaginous fish, and teleost fish. The first fish was not born in the Devonian, but was the earliest vertebrate that emerged 500 million years ago.
From this point of view, fish may be our ancestors! The earliest vertebrates, the Kunming fish and the Haikou insect, produced in my own Yunnan Chengjiang biota (one of the three major camborist biota) at this time the fish are still jawless, as the name suggests, their mouths are like a funnel, mainly by sucking, sucking food and water together, and the gills are filtered. The nailfish also belong to the jawless class. The population of achnap is complex, including cephalic beetles, achphalomorphs, cup beetles and finfish, which vary in size and lifestyle. They do not have true even fins and no bony axis bones. The surface of the body has a well-developed armor composed of bone plates or scales, so it is called a turtlefish.
The nailfish also belong to the jawless class. Populations of armored fish are complex, including cephalic beetles and missing turtles
, cup turtles and finfish, etc., they vary in size and have a variety of lifestyles. They do not have true even fins and no bony axis bones. The surface of the body has a well-developed armor composed of bone plates or scales, so it is called a turtlefish.
Of course, this way of eating is obviously very passive, and with the passage of time, the marine environment has become more and more complex, and animals have begun to evolve in line with the times. This also produces a jawbone, which can open and close the mouth, which also increases the possibility of more predation.
The first animal with the real jaw was the shield fish, whose jaw was evolved from the gill arch of the fish, which is a new milestone in the history of animal evolution. Shieldfish lived around the time of the Silurian period to the same extent that, like the armorfish, the head of the shieldfish was wrapped in many bony pieces of armor to protect against enemy attacks. Not only that, but the shieldfish's chest is also equipped with armor pieces, and the back of the body is covered with scales, making it impossible for the enemy to mouth. We can imagine that shield fish and armorfish belong to the "classic car" family in the ocean at that time, bloated and bulky, and slow to move. However, the internal structure of the two is not the same, and the shield fish has a jaw and even fins, which is a standard fish. Shieldfish are common fossils in the Late Silurian and Devonian periods, but they were completely extinct at the end of the Paleozoic Period.
There is another animal in the shield fish that must be mentioned, that is, the Dunn's fish. The Dunn's fish lives in shallower waters and its main diet is sharks, bony fish, trilobites, ammonites, nautilus and so on. Its body is about 8-10 meters long, weighs up to 4 tons, and its head and neck are covered with thick and hard exoskeletons. Toothless, instead of teeth is the cephalic nail located in the snout, like a knife, very sharp.
It is one of the most ferocious carnivores in the Devonian ocean. But such a top predator can not resist the long river of time in the end, the huge body and size greatly affect its speed and sensitivity, which makes it gradually lose to small sharks and other carnivorous fish in the evolutionary process, coupled with the environmental changes of the earth at the end of the Devonian Period, which eventually makes it leave the stage of biological reproduction and evolution.
Although the Dunn's fish seems to have evolved very advanced, it does belong to the chordate phylum and cannot be called a vertebrate.
Spiny fish, however, were the earliest known jawed vertebrates. The jawbone of the shield fish is called the original jaw, which is not strong enough, and the jawbone at this time is located inside the mouth, and it is not possible to open and close its mouth as freely as it is now. Until 420 million years ago, the modern jaw appeared, this jaw has been reinforced by membranous bone pieces, is the most primitive modern jaw, the earliest evolved modern jaw fish is the initial full jaw fish.
The most distinctive feature of spiny fish is that each fin except the caudal fin has a hard fin in front of each fin. They appeared in the early Silurian period, flourished in the late Silurian and Devonian periods, and gradually declined and died out in the Carboniferous and Permian periods. Typical of these are the gravis, which look like yellow croakers, are small and do not exceed 30 cm in length.
The next class we'll talk about after the spiny fish is the cartilaginous fish we know, which have been found in the ocean from the early zhizhi to the present. However, only two surviving orders remain, the suborder Plate gill (shark, ray) and the full-headed suborder (Silver Dragon).
The last and most abundant of the fish species is the teleost fish. Now we can see the fish
The vast majority belong to the class of teleost fish. There is a class of bony fish called the suborder Meatfin Fish. They are the bony fish that spawned the tetrapods and were key to the evolution of fish to amphibians. In the next issue we talk about amphibians, we will see you in the next issue!
reference
Tong Jinnan, Yin Hongfu, Paleontology
Gao Yan", "Ancient Creatures"
Millais Children's Book Wang Zhangjun's "A Brief History of Life"
Li Jinling, Jin Fan, "Swimming in the Ocean 200 Million Years Ago"
Baidu Encyclopedia
The image comes from the Internet
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