Graptolites are fossils of graptolites,Paleozoic filter feeding animals[4]It is called "graptolite" by scientists because it is compressed into a carbonaceous film in its preservation state, much like the trace written by a pencil on the rock layer.[1]
Graptolite is a general term for graptolites. It is an extinct group of marine organisms, usually belonging toHemichorda, which existed from the Middle Cambrian to the Early Carboniferous.The bones secreted by graptolite worms are called rhabdosome.The size of graptolite is generally several centimeters or tens of centimeters, and the larger one can reach 70cm or more.The composition of graptolite was previously regarded as chitin.The analysis results of Fulkart and Geneo in 1966 showed that the graptolite bone does not contain chitin, but contains many amino acids such as glycine and alanine, which may be derived from hard protein,Transmission electron microscopeThe bone ultrastructure shown below has the appearance of protein bone collagen, which is likely to be composed of bone collagen.Therefore, the composition of graptolite seems to be a non chitin organic matter.[2]
Classification characteristics
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They are generally divided into 6 orders:Dendrobiles(Dendrograptolite)Orthograptolite Dendrograptolite, Tubular Graphophora, Cavity Graphophora, Stem GraphophoraCrustaceansAnd Orthograptolites (Aragonia, Cryptorachia, Axonomia).
Dendrobiles
Multiple horizontal harrows or knots.Many branches, generally irregular.The epidermal tissue at the beginning often evolves into a stem, root or chassis for fixation and living. Some use wire tubes to support floating life.
The graptolite body of the tree graptolite is dendritic, with irregular branches, and no transverse harrow or twist between branches.The normal trachea is straight and zigzag, and may have mouth prickles.With root structure.It survived from Middle Cambrian to Early Carboniferous.
The graptolite body of gridded graptolite is conical, fan-shaped or discoid, with stem and root structure, or the fetal tube is exposed with wire tube.Positive branches, each branch is parallel or nearly parallel, and the branches are connected by transverse harrows in a grid shape.The positive cytoplasm is straight and zigzag, or partially isolated, and the shape of the accessory cytoplasm is uncertain and generally not obvious.It survived from Late Cambrian to Early Carboniferous.
Orthograptolite Dendrograptolite
Without transverse harrow and twist, the branches are regular and often positive.The pipeline is exposed for floating life.
The inverse graptolite has three original branches, each positively branched for several times, generally 3-4 levels, up to six levels.The pen stone branches are mostly flat.The positive cytoplasm is straight and zigzag, and the accessory cytoplasm is short and simple.It survived in the early Early Ordovician.
The graptolite body of the branch graptolite is flat, and there are two original branches. Generally, the positive branches are 5-6 levels, up to 8-9 levels. The graptolite branches are usually longer than one level, and the number of the last branches is very large and nearly parallel.The positive trachea is straight and tubular.It survived in the Early Ordovician.
Guangraptolite
Dendritic or crusty population, with irregular branching of positive and accessory trachea, and undeveloped stem trachea.It survived from Ordovician to Silurian (Guizhou and Shaanxi in China have reported such graptolites).
Ophiograptolite
The pellicular group, the beginning of the positive tubule expanded into a balloon, called the lumen;With a slender, erect neck at the end.It survived in the early Early Ordovician.
Stematograptolite
The population is crusty and irregular in shape. The stem cell contains a stem line with irregular branches, with positive cells, but the accessory cells are not developed.Early Ordovician.
There are three kinds of trachea: positive trachea, accessory trachea and stem trachea.Graptolite branches branched regularly or irregularly.Generally, graptolites are numerous.The epidermis is thick and can be extended laterally into a horizontal rake to connect the adjacent pen stone branches.Graptolite twigs can also be wavy bent to connect adjacent graptolite twigs to form oval meshes, called kinks.It survived from Middle Cambrian to Early Carboniferous.
Crustaceans
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The graptolite body is shell like, like cavity graptolite.However, the space between the positive tubules is thin, with a short and upright neck, and the mouth is deformed, often with a mouth leaf.Paraducts are slender and cylindrical.It is known that it only appeared in Europe from Ordovician to Silurian.
Orthograptolite
There is only one kind of trachea (equivalent to the tree shaped graptolite positive trachea), without accessory trachea and stem trachea.The branches are regular and consist of one to many pen stone branches.The epidermal tissue is thin and supports floating life.Ordovician to Early Devonian.According to the characteristics of the middle axis, it can be divided into the non axial suborder, the hidden axial suborder and the axial suborder.
Anaxial suborder, the initial cell tube grows downward, the fetal tube is exposed, and no axis is formed.There are many graptolites or only one graptolites, which are drooping to the top.The shape of the cell tube can be divided into graptolite, fibrillar graptolite and Chinese graptolite.It can have lateral branches and secondary branches.It survives in the Ordovician Period, and can be seen in the Early Silurian.
Cryptorachia, graptoliths are composed of two or four independently climbing graptoliths, which are double ribbed or single ribbed.Crushing is often separated along the climbing line between graptolite branches.The central axis is developed or undeveloped, located between graptolite branches on the climb.It survived from the middle early Ordovician to the late Ordovician.
The graptoliths of the axial suborder are composed of one or two rows of ascending tubes.The central axis is developed.There are many shapes of cell tubes.These graptolites can be divided into two groups according to the arrangement of the cell tubes on the graptolite body: the double graptolites of the double row cell tubes and the single pen epoch of the single row cell tubes.It is not easy to separate graptolites along the climacteric line between graptolites branches when they break.The epidermal layer of the trachea can degenerate into a grid.The graptolites existed from the middle of Early Ordovician to Silurian;Graptolites from Silurian to Early Devonian.
Fossil research
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According to the state of fossil preservation, the type of symbiotic animals and the bone structure of graptolites themselves, scientists speculate that some graptolites live solidly at the bottom of the submarine camp, for example, most of the tree shaped graptolites have fixed stems, roots and other structures;Another part of graptolites live in floating camp, such as orthograptolites, which have filaments called "wire tubes" to attach to the floating body.
Graptolites can coexist with fossils of brachiopods, trilobites and other animals.But there are also some specific environments where only floating graptolites exist without other organisms or only a few plankton are associated.
Graptolites are usually preserved in black shale. The reason may be that the sedimentary environment at that time was relatively calm, with strong reduction at the bottom, insufficient oxygen, and more hydrogen sulfide, which was not suitable for the survival of benthos. However, graptolites floating in such an environment can live in the surface water body, and the dead body can sink into the water bottom to become a fossil;Another reason may be that when graptolites float from the normal water body to the water body that is not suitable for survival, they die in large numbers and sink into the sea bottom. However, benthic animals on the sea bottom are rare, and if these graptolites are not "eliminated", they will be preserved in large numbers and become fossilized stones.In addition to shale, some graptolite fossils can also be found in fine sandstone, siltstone or limestone.[1]
research meaning
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Graptolite is widely distributed and rapidly evolved. The same species can be found on many continents in the world.According to the stage characteristics of graptolite evolution and special type of geological process, it has unique value in stratigraphic correlation.[3]
