The earth has been evolving for billions of years, from biological explosions to biological extinctions, countless species have performed the legend of life in this vast land!
They are the best witnesses of Earth's history, appearing today as fossils that tell the stories of the past.
Ammonite (Source @ smuki/Fotolia)
Arrow Stone (Source @cometshopnew.com)
Silicified wood (Source@Petrified Forest National Park)
Where do they come from? What kind of fossils have been formed? Let's witness history!
01
The Ordovician after the Cambrian period is known in paleogeology as the Great Explosion of Life. The most widely distributed fossils in the Ordovician oceans were the hornstones of cephalopods.
Hornstones (Source@Nobu Tamura)
The shape of the hornstone resembles the horns of an animal, both straight, curved or coiled. The types of horn stones are Aurora horn stones, horn horn stones, Michlin horn stones, anterior ring horn stones, etc. Among them, Aurora hornstone is a representative of the hornstone fossil.
Aurora Hornstone (Source: Christopher, Tania and Isabelle Luna)
Aurora hornstone is a fossil of marine invertebrate mollusks belonging to the cephalopod order Taphis, trumpet hornstone family, and Aurora hornstone genus, growing geologically from the Ordovician period about 440 million to 510 million years ago.
Aurora Horn stone (Source@Ghedoghedo)
Aurora horn stone, also known as "Chinese horn stone", is mainly produced in the Ordovician strata of Hubei, Hunan, Sichuan, Chongqing and other regions of China.
Aurora Horn stone (Source @ Literature [1])
Aurora hornstone has a hard shell, the shell is either straight or coiled, the surface of the shell has a corrugated stripe, there are many horizontal plates in the shell, the shell length can reach more than two meters, most of which are between tens of centimeters and one meter.
Aurora Horn stone (source @ literature [2])
When sectioned longitudinally, it can be seen pointing at the elongated cone-like body tube at the tip of the shell, while in the center of the cross-section, its rounded tube can be seen. The body tube is smaller than the diameter of the shell, mostly located near the center, and partially close to the edge.
Aurora Horn stone (Source @ Ghedoghedo).
Aurora horn stone has a relatively short life age and can be used as a "standardized stone" to determine the stratigraphic age.
02
Brachiopod phylum, once called molluscs, belonged to benthic, seafaring tentacle crown animals with a pair of hard shells.
Brachiopods (Source@Wilson44691)
But unlike bivalves, their shells are up and down, rather than left and right. The hinge is located on the back, while the front can be opened for cooperative predation or defense.
Fossil brachiopods (Source@Didier Descouens)
They began to evolve in the Cambrian period and flourished most during the Paleozoic period, with the highest level of species diversity.
Fossil brachiopods (Source@Wilson44691)
About 30,000 fossil species were found , but later weakened significantly during the mass extinction event at the end of the Paleozoic period , leaving only a few species to survive to this day.
Brachiopods are small, up to 2.5 cm long and wide, some only about 1 cm, some fossil species can be about 38 cm wide, and the largest extant species are about 10 cm long.
Fossil species are more morphologically variable than existing species, and are generally tongue-shaped or oval-shaped. The surface is smooth, either prickly, or covered with a plate-like structure and crests. Most are pale yellow or white, but some have red stripes or spots, while others are pink, brown or dark grey.
03
Ammonite, a generic term for ammonite subclass species, is a group of extinct marine molluscs with a spiral-shaped shell and wrists.
Ammonite (Source @digitalatlasofancientlife.org)
They appeared on Earth around the early Devonian period of the Paleozoic Era, flourished most during the Mesozoic Period, and finally became extinct at the end of the Mesozoic Cretaceous Period along with dinosaurs, arrowstones and other organisms.
Ammonite (Source@ Jonathan R. Hendricks)
Because ammonites evolve quickly and are widely distributed, they are ideally suited as standardized stones, and geologists can use them to determine the age of formations containing ammonite fossils.
Ammonite (Source@Jonathan350)
Ammonites periodically make ascending movements forward during growth, secreting from the mantle membrane at the rear to support the animal body, increase buoyancy and strengthen the shell.
(Source@Daz Originals)
Therefore, the shell can be divided into two parts: the part where the animal body inhabits without the next door is the living room; the part with a series of next door is the air shell, and the space separated by the two adjacent next doors is called the gas chamber.
Ammonite profile (Source@Lynn Recker)
The contact line next door to the shell wall is called the suture line, which is a very important symbol of ammonite classification. Each next door has a circular next door hole where the body tube is located.
Types of Sutures (Source@Ian Alexander)
The body tube may play a role in linking the software to the shell and adjusting the buoyancy to make the shell sink and float. It is usually located at the edge of the abdomen, but a few categories of body tubes are in the dorsal or near-center position.
Ammonite (Source@Daz Originals)
Ammonite shells come in a variety of shapes: from thin plates to spherical shapes, some are triangular spirals, some are straight rods or rings, and the abdomen is pointed, flat or round.
Ammonite (Source@ jonnysek—iStock/Getty Images)
The surface of the shell is sometimes smooth, sometimes with different types of decoration, common decorations such as growth lines, longitudinal spiral lines, horizontal ribs, tumors, thorns, grooves, ridges, etc.
(Source @Literature[4])
In addition, there are different types of color bands on the surface of the shell, but the vast majority of color bands cannot be preserved on fossils.
(Source@Jonathan R. Hendricks)
04
Along with ammonites, which became extinct in large numbers at the end of the Cretaceous period, arrowstones were also abundant.
Arrow Stone (Source@Ghedoghedo)
Arrowstone appeared from the Early Carboniferous, Jurassic to Early Cretaceous to its peak, most of which were extinct at the end of the Cretaceous, is an important fossil in the marine Jurassic and Cretaceous strata, and today's Europe is its main distribution.
Section of a fossil arrowstone (source@Antonov)
It lives mainly in the continental shelf region and has a body structure similar to that of modern squid, but its inner shell is far more developed than that of the squid. It consists mainly of sheaths, closed cones and anterior nails
3 parts,
Among them, the sheath is most easily preserved as a fossil.
Restoration of arrow stone structure (source @ literature [3])
The arrowstone has about 10 tentacles that protrude from the end of the head with suction basins and hooks that can grab small creatures in the ocean for their food.
It has wing-like fins on either side of the front of its body, which help it control the direction of its advance and swim slowly. When in danger, the arrow stone will also push itself forward quickly by spraying water outwards, thus escaping the danger.
Arrowstone Group (Source@PierreSelim)
The individual size of the arrow stone varies greatly, generally the sheath length is 4 to 12 cm, the total length of the body is generally 24 to 90 cm, and the longest can reach more than 4 meters.
Arrowstone Partial Structured Stone (Source @cometshopnew.com)
In addition to determining stratigraphic age, arrowstones can also determine the water temperature at that time, and provide information for determining paleoclimate and continental drift.
Arrow Stone (Source@Géry PARENT)
05
Silicified wood is a fossil formed by the remains of ancient trees after a long process of chemical element replacement (specifically the process of silicification).
Silicified wood (Source@Michael Gäbler)
Creatures have long appeared on the earth in the form of woody trees, all over the world, and can be found on six continents of the world. Among them, most of them are silicified wood for the purpose of conifer.
Silicified wood (Source@Jon Sullivan)
After a tree collapses, if for some reason it is covered with mud and buried in the ground, the wooden organic objects that make up the trunk will gradually decompose under the action of the temperature and pressure of the surrounding soil layer.
Silicified wood (Source@Clemens Schmillen)
If the moisture, temperature and pressure of the soil covering the trunk and the surrounding environment (including mineral-rich groundwater) meet certain conditions, the impurities decomposed by the wood trunk will combine with the mineral elements in the surrounding soil to form crystals.
Silicified wood (Source@Olga Ernst)
Under the action of groundwater, minerals such as silica, iron sulfide, calcium carbonate and other minerals in the soil layer slowly penetrate into the inner part of the wood trunk, while the organic wood on the outer layer of the wood trunk is decomposed, and these inorganic minerals newly infiltrated into the wood trunk from the soil layer replace the organic wood in the original trunk.
Silicified wood (Source@Jonathan Zander)
The decomposition of one substance (organic wood fiber) occurs simultaneously with the deposition of another substance (inorganic silica), so that one mineral is replaced by another mineral, which is called "accounting", of which silica is mostly composed, so it is also called "silicification process".
Silicified wood (Source@Sergio Kaminski)
After thousands of years of decomposition and replacement, the organic wood of the dried wood is replaced by inorganic silicon calcium crystals. After the silicification process of the wood trunk is completed, the entire wood trunk is similar to a wood trunk jade, which is resistant to preservation.
Silicified wood (Source@Darwin Pucha Cofrep)
The integrity of a silicified wood depends on the time interval between when the tree dies and when the trunk is fully silicified. If the silicification process is fast, it is easy to survive and the shape is complete, while if the silicification process is slow, the part of the trunk will decompose and lose shape when the minerals in the soil layer have not yet penetrated.
Silicified wood (source@Wilson44691)
The Mohs hardness of silicified wood is about 7.0, which is similar to quartz. Complete silicified wood can accurately identify the bark traces, cell shapes and rings of the original tree, making it an important fossil sample.
Silicified wood enlargement (source@Wilson44691)
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