Ammonite (scientific name: Ammonoidea), named after the fact that its surface usually has a chrysanthemum-like line pattern, is a suborder of the mollusk phylloscopus cephalopoda. Ammonites first appeared on Earth around the late Silurian period to the early Devonian period, flourished in the Mesozoic Era (about 225 million years ago), distributed in the Triassic oceans around the world, and finally became extinct in the late Cretaceous Period (about 65 million years ago) along with dinosaurs.
Ammonites are generally divided into about 80 superfamilys in 9 orders, about 280 families and about 2000 genera, as well as many species and subspecies. Cephalopods, organs of motion in the head. There is a hard shell on the outside of the body, similar in shape to the Nautilus. In the evolution of cephalopods, only the Nautilus also carried a heavy hard shell, slowly swimming in the water, relying on the hard shell to protect itself, while other species have evolved to shed their hard shell and move forward lightly. According to the way the Nautilus moves, ammonite is also an animal with an inexhaustible swimming speed and poor motor coherence.
Restoration of ammonite
Seeing the restoration of ammonites, the impression in everyone's mind may be the appearance of their close relatives, nautilus, and it is generally difficult to say the specific difference between them and nautilus. Some ammonites have the same shell as the living nautilus, and also have a separated air chamber inside the shell. Looking at the shapes alone, it seems difficult to distinguish them.
Nautilus and ammonite restoration with growth stripes, transverse ribs
Ammonites periodically make ascending movements forward during their growth, and behind them are secreted by the mantle membrane next door (next door refers to the membrane-like material separated by two adjacent air chambers, and after becoming fossilized, its form is like a partition. ) 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 inhabits without the next door, called 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, most of the ammonite has 26 air chambers, and the nautilus that is still alive is generally 30. The ammonite is next to a curved surface with anterior and posterior folds relative to the Nautilus, often with complex shapes, especially at the near shell wall where the folds are very strong.
The contact line between the next door and the shell wall is called the suture line, which is a very important symbol in the classification of ammonites (the suture line refers to the line at the junction between the next door and the shell surface. The sutures of the Nautilus are curved in the same direction, while the fossils of ammonite are various fluctuating and distorted shapes, and the sutures of ammonite have evolved to be more complex than those of the Nautilus, because this can increase the contact surface between the flesh and the shell, make the internal structure more stable, and enhance the strength of the shell to meet the needs of moving in deep water and avoiding predators.
Each next door has a circular next door hole where the body tube is located. 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.
The degree of unwinding of ammonite shells is very different, and can be roughly divided into loose rolls, contact rolls, outer rolls, semi-outer rolls, semi-inner rolls and inner rolls. The shell is also diverse in shape: from thin plate to spherical, some are triangular spiral, some are straight rod or ring, the abdomen is pointed, flat or round, etc.
Various special-shaped shells (image source: see watermark)
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 of ammonite is covered with a mouth cover. The mouth cover has a single flap (that is, a single mouth cover, the Paleozoic mouth cover is rarely mainly a single mouth cover, and the single mouth cover is a piece of thin sheet, which cannot completely close the mouth, and it is also easy to decompose and disappear. ）
Some have double lobes (i.e., double-mouthed lids), which appeared in the Jurassic: consisting of a pair of roughly triangular, slightly outwardly convex calcareous tablets with a straight joint line between the two flakes. ）
Some are also made up of double-lobed joints (called closed mouth covers, which are only found in the Late Cretaceous Period, consisting of three layers, with a thin outer layer, a surface with spotted, granular, ridged and grooved concentric lines, thick middle layers, foamy or tubular structures. The inner layer is thin and the inner surface is smooth. ）
Usually, the mouth cap is separated from the ammonite shell and preserved, and the ammonite fossils with the mouth cover are very rare.
15 is a closed mouth cover, 23 is a double mouth cover, and 46 is a single mouth cover.
Image source: See watermark
The size of ammonite shells varies greatly, with the average shell only a few centimeters or tens of centimeters, the small one only 1 centimeter, and the large one reaching 2 meters.
Ammonite fossils are found in shallow sea sediments and symbiosis with many marine fossils. Through the determination of paleomagnetism and paleothermia of ammonite-bearing strata, lithology and lithofacy analysis and the study of ammonite paleoecology, it is speculated that ammonite inhabits the sea with a certain depth in the tropical to temperate zone, and has different living habits due to the thickness of the shell wall, the shell shape and the shell surface decoration, for example, the type with thick shell wall and the thick shell decoration is the less active type; the shell wall is thinner, the surface is smooth and the shell shape is the more active type of living in the deeper water body.
Prismatic ammonites that appeared in the early Devonian period
Ammonite fossils have the characteristics of rich shell decoration, thick shell wall and beautiful appearance. Ammonite fossils were found in Dongyuan Zengkeng, with a total of more than 200 pieces, which is currently the largest number of ammonite fossils found in the country, the richest variety and the largest ammonite fossil group, of which there is a 42 cm extra-large ammonite fossil, which is the crown of the southern country. Due to their well-preserved appearance and peculiar ornamentation, these fossils look more like chrysanthemums growing in stone, and their shape is cute.
Ammonite fossils
Ammonites evolve rapidly, have a large distribution range, and are easily identifiable, making them the most effective standardized stones for dating rocks, dividing and comparing formations, and geologists can use them to determine the age of formations containing ammonite fossils. It has great scientific value in stratigraphy and paleontology. At the same time, ammonite has a good collection value because it is well preserved in the formation and has a beautiful and harmonious curve.
Tooth ammonites appeared in the Late Permian to Triassic
It contains a variety of ammonites in the Paleozoic and Mesozoic strata of China, especially the Early Devonian ammonite group in Guangxi, the Permian ammonite in South China, the Triassic ammonite in Guangxi, Qinghai and Tibet, and the Jurassic and Cretaceous ammonites in Tibet.
Ammonite fossils have been found in the marine strata of Guangxi, Guizhou, Qinghai and Tibet in China, especially in the Mount Everest region of Tibet, there are a large number of ammonite fossils produced, and even readily available. Because more than 200 million years ago, it was once the ancient Himalayan Sea, and due to the orogeny movement, the earth's crust rose and the seabed became a mountain. Therefore, the ammonite living on the bottom of the ocean is presented on the ground, becoming a witness to the changes in the movement of the Himalayan mountain crust, and also providing favorable evidence for the restoration of the local paleo-ecological environment.
Section and outer surface of ammonite fossils
The longitudinal profile of the ammonite fossil is beautifully spiral-shaped, brownish yellow translucent, the color is like amber, and the folk in Fujian and Taiwan believe that ammonite can be transported and qi, bringing people good luck, good feng shui, multi-joy collection, indoor pairs of placement. The individual is large, the color is beautiful, and the exquisite can be called a gem-level collection. However, the overall production of ammonite is very large, and its scientific research value exceeds the collection value.
(Graphic data from the Network)