Complete detailed information on ammonoids (a subclass of Molluscs, Cephalopoda)

Ammonite, a subclass of the phylum Cephalopod Molluscs. Ammonites are not living animals but extinct marine invertebrates that lived from the Devonian to the Cretaceous. It first appeared in the early Devonian period of the Paleozoic era (about 400 million years ago), flourished in the Mesozoic era (about 225 million years ago), and was widely distributed in the Triassic oceans around the world. Thousands of years) extinct. Ammonites are usually divided into 9 orders, about 80 superfamilies, about 280 families and about 2000 genera, as well as many species and subspecies, etc. Nautilus is a close relative of it. Basic introduction Chinese name: Ammonite Latin scientific name: ammonite Alias: Snake Stone Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Subclass: Ammonoidea Family: 280 Genus: 2000 Distribution area: Marine Basic introduction, ammonite - evolutionary development, detailed information on ammonite, appearance characteristics, ammonite shell structure, ammonite suture changes, systematic classification, distribution, evolutionary development, collection value, research significance, others, incarnation of the god Amun They are related to snake stones, ancient ammonites, and octopuses and squids. It basically introduces the cephalopod molluscs of the ammonoid subclass (Ammonoidea), with more than 600 species. It existed in large quantities in the late Paleozoic and Mesozoic eras. Extinct about 100 million years ago. Its fossil shells are either straight or rolled, with a diameter of up to 200 cm. The inner shell is divided into many small spaces to provide buoyancy. It lived from the Devonian to the Late Cretaceous and is named because its surface usually has chrysanthemum-like lines. Knowledge about ammonoid animals comes mainly from ammonite shells and operculum preserved as fossils and from observations of the distribution and preservation status of ammonites in strata and based on comparisons with nautiloids living in modern oceans. Ammonites evolved from the Nautilus order in the early Devonian period 400 million years ago. During the next 370 million years, they existed in large quantities in the world's oceans until the Cretaceous period. Things like belemnites and terrestrial dinosaurs became extinct from the earth at the same time. Ammonites - Evolutionary Development Ammonites first appeared in the early Devonian period of the Paleozoic Era about 400 million years ago. They flourished in the Mesozoic Era and were widely distributed in the Triassic oceans around the world. Therefore, it predates the appearance of dinosaurs by 170 million years. Ammonites evolved from nautiluses and are cephalopods with organs for movement in their heads. There is a hard shell outside the body - this is the dwelling it built itself, similar in shape to a nautilus. During the evolution of cephalopods, except for the nautilus, other species no longer carry a heavy hard shell, but move forward lightly. Ammonite shells come in various shapes, including triangular, cone-shaped and rotating shapes, with rotating shells being the most common. The shell of ammonite is also divided into front, back, back and abdomen;. The size of ammonite shells varies greatly. The average shell is only a few centimeters or tens of centimeters, the smallest is only 1 centimeter, and the large one reaches 2 meters.

"Prism ammonite" is the earliest ammonite to appear. There was a mass extinction of species 245 million years ago, causing "ammonite" to disappear from the earth. Later came the "odontoliths," and when this animal became the dominant marine animal in the Triassic, dinosaurs also began to live on land. However, ammonites disappeared at the end of the Triassic about 200 million years ago. Later, there were also "belly ammonite", "oyang stone" and "belemnite". Ammonite detailed information Appearance characteristics Cephalopods, the organs of movement are in the head. There is a hard shell outside the body, similar in shape to a nautilus. The size of ammonite shells varies greatly. Generally, the shells are only a few centimeters or tens of centimeters, and the smallest ones are only one centimeter. The largest ones are larger than the large millstones in rural areas and can reach 2 meters. Ammonite shells come in a variety of shapes, including triangles, cones, and spirals. Generally speaking, there are outer-rolled circular shells, inner-rolled circular shells, rod-shaped shells, tower-shaped shells, outer-rolled triangular shells, irregular spiral shells, etc. Round shells with inner and outer curls account for the vast majority of ammonites. The ammonite shell is also divided into front, back, back and abdomen.

This is the same as modern nautilus. The opening is the front and the original shell is the rear. The outer part of the gyroscope is the abdomen, and the surface corresponding to the abdomen is the back. Ammonite shell structure The shell of ammonite is a conical tube mainly composed of calcium carbonate. The beginning of the shell tube is small, usually spherical or barrel-shaped, and is called the carcass. The shells of most ammonites are convoluted in a plane with the carcass as the center, and a few are in straight shells, spirals or other irregular shapes. Each shell ring of the flat convoluted shell is called a gyroscope. Its periphery is the abdomen. The side surrounding the inner gyroscope is the back. The shell surface between the abdomen and the back is the side. During the growth process, ammonite animals periodically move forward in an ascending manner, and behind them, the mantle secretes partition walls to support the animal body, increase buoyancy and strengthen the shell. Therefore, the shell can be divided into two parts: the part where the animal body lives without partitions is called the living room; the part with a series of partitions is the air shell, and the space separated by two adjacent partitions is called the air chamber, and the partitions are A curved surface, usually of complex shape, with strong folds especially near the shell wall. The contact line between the partition wall and the shell wall is called a suture, which is a very important symbol in the classification of ammonites. Each partition has a circular partition hole where the body tube is located. The body tube may play the role of connecting the software and the shell and adjusting the buoyancy to make the shell sink and float. It is usually located at the edge of the abdomen, but in a few cases it is located dorsally or near the center. The degree of convolution of ammonite shells is very different, and can be roughly divided into loose scroll, contact scroll, external scroll, semi-external scroll, semi-internal scroll and internal scroll. The shapes of the shells are also diverse: from thin plates to spherical shapes, some are triangular and convoluted, some are straight rod-shaped or ring-shaped, the abdomen is pointed, flat or round, etc. The surface of the shell is sometimes smooth, and sometimes has different types of decorations. Common decorations include growth lines, longitudinal spiral lines, transverse ribs, knobs, thorns, grooves, ridges, etc. These decorations vary depending on thickness, strength, density, and direction. and combine with each other to create many variations. 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. The shell mouth of the ammonite is covered with a operculum. Some operculums have a single flap (single operculum), some have double flaps (double operculum), and some have double flaps fused (combined operculum). Usually the mouth cover is kept separately from the ammonite shell. Fossils of ammonites with openings are rare. The systematic classification signs of ammonites include shell shape, degree of convolution, shell surface decoration, body tube position and suture characteristics, etc. Ammonite suture changes Among them, the characteristics of the sutures are of particular importance. Each suture can be divided into an outer suture and an inner suture. The outer suture is a section of suture on the outer surface of the shell, and the inner suture is a section of suture on the back surface. The basic elements of the suture are the lobe and saddle. The lobe is the part of the suture that bends backward, and the sella is the part that bends forward. According to the distribution positions of the leaves and saddles, they are called ventral leaves (or ventral saddles), dorsal leaves (or dorsal saddles), lateral lobes (or lateral saddles), etc. A series of folds in which the sutures do not completely become independent saddles and lobes on the lateral surface are called costal lines; a series of secondary saddles and lobes located between the ventral lobe and the first lateral lobe are called occasional saddles and lobes. There are two ways of proliferating leaves and saddles: ① Saddle-split type, in which the saddle is split to form independent leaves and saddles; ammonite ② Leaf-split type, in which the leaves are split to produce new leaves and saddles. According to the shape of the leaves and saddles, ammonite sutures can be summarized into 4 basic types: ① Edgeless ammonite type: the leaves and saddles are complete, few in number, and there is only one wide rounded leaf on the side, found in Devonian ammonites; ② Prism ammonite type: leaves and saddles are complete, more in number, and the leaves are pointed, found in Devonian to Triassic ammonites; ③ Tooth ammonite type: saddles are complete, leaves are serrated, found in Carboniferous to Triassic ammonites; ④Ammonite type: The leaves and saddles are strongly bifurcated or toothed, found in ammonites from the Permian to the Cretaceous. The characteristics of sutures are the main symbol for classifying orders and suborders, and are also important symbols for classifying superfamilies, families, genus, and even species. The position and direction (forward or backward) of the carcass and body tube are also meaningful at the level of order and suborder. Shell decoration plays an important role in identifying genus and species, as well as certain families. The shape of the shell and the degree of convolution are signs of genus and species classification.

Therefore, some people also conceive that the baculites and the non-edge ammonites evolved from the orthogonal stones with oval carcass and ventral tubes at almost the same time. Ammonite fossils are produced in shallow sea sedimentary strata and occur together with many marine biological fossils. Through the paleomagnetism, paleotemperature measurement, lithology and lithofacies analysis of ammonite-containing strata, and the study of ammonite paleoecology, it is inferred that ammonites inhabit sea areas with a certain depth from the tropics to temperate zones, and are affected by shell walls. Different thickness, shell shape and shell surface decoration have different living habits. For example: the type with thicker shell wall and thick shell decoration is the less active type; the type with thinner shell wall, smooth surface and pointed pancake shape The shell-shaped ones are the more mobile types that live in deeper water bodies. Ammonites evolve rapidly, are widely distributed and easy to identify. They are the most effective standard fossils for dividing and comparing strata. According to the vertical evolution of ammonite in the stratum, it is divided into quite fine ammonite zones. For example, in the Triassic, Jurassic and Cretaceous periods of the Mesozoic Era, more than 30 ammonite belts can be divided into each period. The average duration of each ammonite belt is between 1 and 2 million years. In Western Europe, The Serbukhovian strata in the late Early Carboniferous of the Paleozoic era are divided into 30 ammonite belts, and the average duration of each ammonite belt does not exceed 500,000 years. Determining the absolute age of strata using isotopes and other methods is far from achieving this accuracy. There are various ammonites in the Paleozoic and Mesozoic strata in China, especially the Early Devonian ammonites in Guangxi, the Permian ammonites in South China, the Triassic ammonites in Guangxi, Qinghai and Tibet, and the Jurassic and Cretaceous ammonites in Tibet. meaning. There are records of ammonite fossils being found in the marine strata of Guangxi, Guizhou, Qinghai and Tibet in my country. Especially in the Mount Everest area of ​​Tibet, a large number of ammonite fossils are produced and even readily available. Because during the Mesozoic Era, there was the ancient Himalayan Sea. As the crust rose due to tectonic movements, the seafloor turned into mountains, and ammonite fossils were also exposed. People once called this kind of animal whose convoluted shell is decorated with ribs, edges and ridges “Ammon’s horns” or “snake-stones”. During the evolution of cephalopods, only the nautilus still carries a heavy hard shell and swims slowly in the water, relying on the hard shell to protect itself, while other species have shed their hard shells during evolution. , move forward lightly. Judging from the movement of the nautilus, ammonites are also animals that do not swim very fast and have poor movement coherence. There are many shell decorations on the surface of the ammonite shell. Shell decoration is the general term for growth lines and growth lines, which are parallel to the screw mouth. Some have vertical stripes that are parallel to the spiral direction of the shell, and some have horizontal stripes that are perpendicular to the direction of the shell. Ammonite shells are mainly composed of calcium carbonate and are mostly flat-spun shells. The shell is spirally rolled in a plane with the carcass as the center. A few shells are straight shells, spiral shells or other irregular shapes. During the growth process, ammonite animals periodically secrete partition walls from the mantle. The space separated by two adjacent partition walls is called an air chamber; the contact line between the partition wall and the shell wall is called a suture; each partition wall has a circular partition wall. The foramen is where the body canal is located, usually on the edge of the abdomen, and rarely on the back or near the center. The surface of the shell is sometimes smooth, sometimes decorated with growth lines, longitudinal spiral lines, transverse ribs, knobs, spines, grooves, ridges, etc. The shell mouth of the ammonite is covered with a mouth cover. The character of sutures is of particular importance in the systematic classification of ammonites. Each suture can be divided into a section on the outer surface of the shell called an outer suture, and a section on the back surface called an inner suture. The basic elements of the suture are the lobe and saddle. The lobe is the part of the suture that bends backward, and the sella is the part that bends forward. According to the distribution position of the lobes and saddles, they are called ventral lobes (or ventral saddles), dorsal lobes (or dorsal saddles), lateral lobes (or lateral saddles), etc. A series of folds on the sides that do not completely become independent saddles and lobes is called a rib system. According to the morphology of leaves and saddles, ammonite sutures can be summarized as edgeless ammonite, edged ammonite, toothed ammonite and ammonite. The exit of the software part is the shell mouth. The shape of the shell mouth is also different, including round and oval, and generally has an abdominal curve. The shell opening is covered and is called the operculum. Its composition is calcareous or horny. After the soft part shrinks into the shell, the mouth cover is tightly closed to protect the soft part.

The operculum only appeared in the early Devonian period, and is divided into two categories: one is the single operculum that appeared in the Triassic, which is a thin piece of horny bag that cannot completely close the mouth; the other is the single operculum that appeared in the Mesozoic Era. The double operculum, which only appeared in the Luoji and Cretaceous periods, is composed of a pair of calcareous plates that are roughly triangular and slightly protruding outward. Collection value Ammonite fossils are produced in shallow sea sedimentary strata and occur together with many marine biological fossils. Through research, it is speculated that ammonites inhabit sea areas with a certain depth from the tropics to temperate zones. Ammonites are the most effective standard fossils for dividing and comparing strata, and can be divided into quite fine ammonite zones. Various ammonites contained in the Paleozoic and Mesozoic strata in China are of great significance. Ammonites China's Devonian ammonites are mainly produced in Nandan, Guangxi and other places. Carboniferous fossils are also mainly produced in Guangxi. Permian ammonites are widely distributed in southern my country. Triassic ammonites are mainly found in Guizhou, Tibet, Sichuan, Hubei and other places. There are a large number of Jurassic ammonite fossils in the Mount Everest area of ​​Tibet, which are even readily available, because more than 200 million years ago, there used to be the ancient Himalayan Sea. Due to orogeny, the crust rose and the seafloor turned into high mountains. Therefore, ammonites living at the bottom of the ocean appear on the ground and become witnesses of changes in crustal movements in the Himalayas. They also provide favorable evidence for the restoration of the local paleoecological environment. There are very few ammonites in Cretaceous China. The longitudinal section of the ammonite fossil is a beautiful spiral shape, brownish yellow and translucent, and the color is like amber. Folks in Fujian and Taiwan believe that ammonite can transport and circulate qi, and bring good luck and good feng shui to people. Many people like to collect it. Placed in pairs indoors. The individual ones are huge, the ones with beautiful color are expensive, and the exquisite ones can be called gem-level collectibles. In 2012, 70cm diameter ammonite slices were sold in the Taiwan market, with a pair worth NT$800,000. However, the overall output of ammonites is very large, and its scientific research value exceeds its collection value. Research Significance Ammonites are the most useful fossils for estimating the age of rocks. Using ammonites, experts can divide geological time to an accuracy of 500,000 years. Compared with the earth's age of 4.6 billion years, 500,000 years is a very short period of time. Most of the Jurassic and Cretaceous periods were divided using ammonites in this way. Ammonite fossils are widely distributed—fossils of the same species may be found thousands of miles apart. This is because during the Jurassic, Pangea began to break up, providing a channel for ammonites to spread around the world. Other Incarnations of God Amun and Snake Stones The scientific name of ammonite comes from the ancient Egyptian god Amun. The priests used sheep heads to express the image of the god Amun. The curled sheep horns resemble ammonite shells and are a symbol of the sheep god. In 88 AD, the famous Roman naturalist Pliny was the first to mention ammonites in his writings. He called the ammonite the horn of the god Amun. Amun was originally the Egyptian god of wind and air. From 2000 BC to 1360 BC, Amun occupied a prominent position among the Egyptian gods and was revered as the first creator god. The Thebes, which believed in Amun, built There are temples at Karnak and Luxor dedicated to Amun. One of the representative symbols of the god Amun is a ram with two spiral horns, which is very similar to the coiled shell of ammonite. Therefore, Pliny regarded ammonite as a sacred stone and believed that it had the magical power to evoke the future.

In the Middle Ages, people regarded ammonites as coiled headless snakes, making ammonites full of mystery. The British called ammonite "snake stone". A small town in Yorkshire, England has always said that the ammonite is a headless snake whose head was beheaded by the 7th century saint Hilda. Therefore, the city emblem of this small town has three snake-headed ammonites. It is said that wizards can use ammonite to make sleeping gods appear holy. The incarnation of the god Amun. Ancient ammonite-like creatures are related to octopus and squid. 400 million years ago, there was an ancient ammonite-like creature, nautiluslike, wandering in the vast ocean, searching for fish and other prey. Nautiluslike had dozens of tentacles and lived in spiral or conical shells, which paleontologists have long hypothesized. But a new study has found that many members of this ancient family are sedentary, spending most of their time on the seafloor where methane bubbles bubble up. These creatures are related to octopus, squid, and cuttlefish.