First, the characteristics of coelenterates
Coelenterates, including extant and extinct hydra, jellyfish, coral, etc. , belonging to the lower double-embryo multicellular animal, is named digestive cavity or coelenterate because of its central cavity for digesting food. The phylum has the following characteristics: ① it is a multicellular metazoan with a clear division of labor; ② The body wall is composed of ectoderm, endoderm and mesoderm, and there is a cavity in the middle, which is called body cavity. The upper mouth is not only the entrance of food, but also the discharge hole of waste, and there are one or several circles of tentacles around the mouth (Figure 2-7); (3) Coelenterates are mostly marine animals, and a few live in fresh water. There are two kinds, the stationary hydra type and the floating jellyfish type. The hydra type is cylindrical, single or group, and the jellyfish type is umbrella-shaped (Figure 28); ④ Ectodermal cells can secrete calcium or horny exoskeleton, but some coelenterates have no bone capacity.
Figure 2-7 Structure of Anemone
(According to Paleontology Department of Wuhan Institute of Geology 1983)
Figure 2-8 Comparison of jellyfish type (a) and hydra type (b)
(quoted from He Xinyi, 1987)
According to the soft structure, whether there are stinging cells and bones of coelenterates, coelenterates can be divided into stinging cells and non-stinging cells. Spinibarbus subfamily can be divided into four classes: Hydra, Primitive Jellyfish, Cephalotaxus Cephalotaxus and Coralline Algae, among which Coralline Algae have the most fossils and have the greatest stratigraphic and ecological significance.
Corals include modern anemones, stony corals, red corals, extinct four corals and horizontal corals. , are marines, individually or in groups. Most of them have exoskeletons, mainly calcium. According to the characteristics of tentacles, the number and arrangement of diaphragms and the characteristics of hard bones, the software can be divided into four subclasses: transverse coral, four corals, six corals and eight corals, among which four corals and transverse corals have more fossils, which is of great significance to stratigraphic indication.
Second, four coral subclasses.
(A) the basic characteristics
Four coral forms can be divided into single type and compound type. The single shape is mainly pyramid or curved cone, which can be subdivided into several types according to the size and bending degree of coral apex angle (Figure 2-9).
Figure 2-9 Monomer Shape of Four-ray Coral
(According to Paleontology Department of Wuhan Institute of Geology 1983)
Composite coral consists of many individuals, which are divided into massive and massive. Individuals who are not in contact with each other are called plexiform complexes, which are divided into dendritic and full-shaped; Closely connected individuals without gaps are called massive complexes, which are divided into polygons, polygonal stars, embedded and interconnected (Figure 2- 10).
Figure 2- 10 Complex types of four corals
(According to Paleontology Department of Wuhan Institute of Geology 1980)
(2) External structure
The external structure includes the outer wall, surface wall and calyx of coral, which are described as follows:
◎ Outer wall: The outer wall of individual coral is called the outer wall, which is the basic structure of early coral development. With the outer wall, other structures can be attached and appear one after another. But in adulthood, the outer wall is often not an independent structure, and sometimes it is formed by thickening the outer end of the partition wall.
Surface wall: A layer of gray film on the surface of the outer wall, which is the growth line secreted by the drooping part of the coral body wall during the upward movement. The thin ones are called growth lines or horizontal lines, and the thick ones are called growth wrinkles. The formation of growth lines and growth wrinkles is related to the growth cycle of corals. According to the research of modern coral, each thin growth line represents a day and night, while each growth zone and growth wrinkle represent the growth cycle of month and year respectively.
Calyx: cup-shaped cavity at the end of coral body, where corals inhabit and grow. It has various shapes, such as cup, cone, saucer and so on. The calyx characteristics of early corals and adult corals are often different.
(3) Internal structure
The internal structure of coral can be divided into vertical structures, such as partition walls; Horizontal structure, including horizontal plate, scale plate and foam plate (Figure 2- 1 1, Figure 2-12); Shaft structure (Figure 2- 13), central axis and central column.
Coral begins to form radial folds at the bottom of the body while secreting the outer wall and the outer wall, and the upward protruding part of the folds secretes to form an upright plate-shaped partition wall to support the soft body. The next door of the four corals appears in a certain order, the longest is the primary next door, and then the first and second next doors grow in turn. The concave part between the partition walls forms a series of regular curved small plates when moving up intermittently, which are called scales. Scales only develop between adjacent walls and the edge of coral body (Figure 2- 12), and they are arranged concentrically or herringbone in section (Figure 2- 12-2). If the depression between the partition walls is not deep, the secreted small plates become irregular in size, grow ahead of the partition walls and cut through them, which is called foam plates (Figure 2- 12 4). The central flat part of coral soft body often moves up in stages, and secretes a series of horizontal or inclined transverse plate supports. Transverse plate can be divided into complete transverse plate and incomplete transverse plate. Incomplete transverse plate means that the upper and lower transverse plates are staggered or different (Figure 2- 1 1). Some corals can have a solid "gray column" in the center, called the central axis, which is formed by the expansion of coral partition walls at the inner end; Other coral structures with cobweb-shaped cross sections are called central columns, and the central axis and central columns are collectively called axial structures (Figure 2- 13).
Figure 2- 1 1 coral lateral type
(According to Paleontology Department of Wuhan Institute of Geology 1980)
1. Complete transverse plate; 2. Arch on the transverse plate; 3. Incomplete transverse plate; 4. Differentiation into central transverse plate, edge inclined plate and scale plate; 5. Divided into internal inclined plate and horizontal transverse plate.
Figure 2- 12 Scale plate and foam plate
(According to He Xinyi 1987)
Figure 2- 13 Shaft Structure
(According to He Xinyi 1993, comprehensive)
1. Central axis; 2. Central column
According to the combination of longitudinal structure, transverse structure and axial structure, the evolution process from simple to complex can be divided into three structural types, namely single belt type, double belt type and triple belt type, of which one foam type belongs to special double belt type (Table 2-4).
Three. Transverse coral subclass
Lateral coral, named after its lateral development, is an extinct subclass of Corallina. Most of them are complex, and they are also divided into two categories: block and clump. The individual cross section of the block complex is polygonal and half-moon, and the shape of the complex is spherical, semi-spherical and discus-shaped. The individual of cluster complex is cylindrical, and the shape of complex is sheng-shaped, dendritic and chain-shaped.
Table 2-4 Table of Four Types of Coral Structure Combination
In the skeleton structure of transverse coral, the partition wall is underdeveloped or no partition wall. Its transverse plate is complete or incomplete, complete with horizontal, concave and arch, incomplete with staggered, funnel and foam shape (Figure 2- 14), and most of them are scale-free. Another main feature of transverse coral is that it has the characteristic structure of communicating individual cavities or connecting individuals with each other, which is called connecting structure, and can be further divided into three types: connecting holes, connecting pipes and connecting plates (Figure 2- 15).
Fig. 2- 14 transverse plate types of transverse plate corals (all longitudinal sections)
(According to Paleontology Department of Wuhan Institute of Geology 1980)
The left picture shows the complete transverse plate; The last three pictures are incomplete horizontal plates.
Figure 2- 15 Connection structure of transverse coral
(According to He Xinyi 1993)
Four. Ecological and geographical historical distribution of corals
(a) coral ecology
Coral is a benthic marine animal, which generally lives in a warm shallow sea environment with a water depth of100 ~ 200 m. There are two main ecological types: non-reef-building corals and reef-building corals. Non-reef-building corals are mostly single, with strong adaptability and can survive at various depths and low temperatures. Most reef-building corals are complex and have a narrow living range. They live in warm and clean shallow seas with normal salinity. The most suitable water depth is about 20 m and the water temperature is 25 ~ 30℃. At present, there are a large number of coral reefs in the latitude 30 north and south of the equator, but they are mainly distributed in the tropical and subtropical shallow waters between latitude 28 south and north, especially in the area between latitude 13 near the equator of the Pacific Ocean. Therefore, according to the strict ecological environment and certain distribution laws of reef-building corals, we can infer the equatorial position, paleolatitude and paleoclimate changes in various historical periods, and provide important paleontological evidence for continental drift and plate tectonics.
(2) Geographical and historical distribution
Tetracorals first appeared in the Middle Ordovician and became extinct at the end of Permian. Its development has four prosperous periods, namely, Late Ordovician to Middle Silurian, Early Middle Devonian, Early Carboniferous and Early Permian. Transverse corals began to appear in the Late Cambrian and flourished in Silurian and Devonian, but decreased greatly in Carboniferous and almost disappeared at the end of Paleozoic.
Verb (abbreviation of verb) identification method of coral fossils
recognition methods
Specimens must be combined with thin film or light film at the same time. Thin slices (or light slices) must have two kinds: horizontal slices and vertical slices, in order to fully understand the structure of coral bodies.
1. Cross section
You can see scales, transverse plates (which can only be seen if the transverse plates are uneven), foam plates, central axis and complex columns in the middle, and the individual contact relationship of the complex.
(1) The difference between scale plate and horizontal plate: the real scale plate is regular and distributed at the edge of coral body, while the horizontal plate is generally not as regular as scale plate and distributed at the center of coral body.
(2) In general, scale board and foam board will not exist at the same time.
terrace cut slice
There are two situations:
(1) Through the section of coral individual center, the partition wall cannot be cut (but it can sometimes be seen if it is as long and dense as the center), and the structures shown on other sections can be seen.
(2) When the coral edge is sliced, no axial structure can be seen, but other structures can be seen.
(2) identification step
1. First, identify four corals and horizontal corals.
The shape and basic structure are different: coral is large, simple and complex; The longitudinal structural partition wall is the most developed; The lateral structure is complex. Transverse coral is very small, generally less than 5mm, which is very complicated; The partition wall in the row structure is underdeveloped or does not exist, but the transverse plate in the row structure is extremely developed.
2. It was identified as four corals.
If it is determined to be luminous coral, determine its structural type: single belt, double belt, triple belt and foam type. Then observe from the outside to the inside.
(1) Look at the appearance first, and distinguish between monomers and compounds, and compounds should distinguish between blocks and clumps.
(2) Observe the thickness of the external wall.
(3) the characteristics of the next door-refers to the shape and series.
(4) the shape and development degree of the transverse plate (shape refers to flat or bending, and development degree refers to width).
(5) The arrangement law, density and width of scale bars.
(6) The width of the foam belt composed of foam boards, the size and regularity of the foam boards.
(7) The existence and development of central axis and complex central column.
3. It is identified as a transverse coral.
(1) Pay attention to the external morphology (block or cluster) and connection structure.
(2) To understand the various structures and performances on different sections.
VI. Skills Training —— Identification of Common Coral Fossils
(1) objective requirements
(1) has mastered the main structural characteristics of coral through practice.
(2) Understand the general characteristics and basic structure of transverse coral.
(3) Master a certain number of fossil representatives of four corals and horizontal corals.
(two) the use of instruments, tools and supplies.
Multimedia equipment, binocular stereo microscope, magnifying glass (15 ~ 20×), experimental report, fossil specimen.
(3) Requirements of evaluation report
(1) Each person shall observe at least 10 specimens, describe 5 specimens, draw the main structures and mark them.
(2) Compare the similarities and differences between four corals and horizontal corals.
(4) Identify the content
1. Identification of common coral fossils
Streptelasma Hall, 1947 (torsion center coral) (1- 16 in Figure 2): single body, pyramid-shaped or nearly cylindrical, with thick knots on narrow sides. There are many next doors, some long and some short, and the long next door is twisted on the shaft. Usually has a narrow main internal groove. The center of the transverse plate is raised without scale. Middle ordovician-middle SILURIAN.
Tachylasma Grabau, 1922 (fast-wall coral) (Figure 2- 16-4): a small wide cone monomer. The partition walls are arranged in a quarter-feather shape, and the two side partition walls and the opposite two side partition walls are particularly thickened at the inner ends to form a rod shape. The main septal wall shrinks, the main internal sulcus is obvious, and the secondary septal wall is short. The transverse plate is convex. Without scale. Carboniferous-Permian.
Kueichouphyllum Yu, 193 1 (Guizhou coral) (Figure 2- 16 bis): Monomer, curved cone column, large. There are many next doors and some gathering centers on the first floor. The length of the secondary partition wall is 1/3 ~ 1/2 of the coral radius. The main transverse plate belt thickens. The main internal sulcus is clear. The bandwidth of the scale plates is equivalent to the length of the secondary partition wall, and the scale plates are arranged in a regular concentric shape. The transverse plate bulges towards the center in the form of foam. Late Early Carboniferous.
Fig. 2- 16 Fossil Representative of Tetracoralline Subclass
1.Streptelassma (torsion center coral) (1a. Longitudinal section,1b. Cross section); 2. Guizhou coral (cross section); 3. Shizhan (Shizhu Coral) (3a. Cross section, 3b. Longitudinal section); 4. Fast cell body (fast wall coral) (4a. Cross section, 4b. Longitudinal section); 5. Shuang Ye coral (exfoliated coral) (5a. Cross section, 5b. Longitudinal section); 6. Canine (Canine Tooth Coral) (6a. Cross section, 6b. Longitudinal section); 7. False coral (7a. Cross section, 7b. Longitudinal section); 8. Hexagonal Coral (Hexagonal Coral) (8a. Cross section, 8b. Longitudinal section); 9. Liangshan Coral (9a. Cross section, 9b. Longitudinal section); 10. polyhedron (10a. Cross section, 10b. Longitudinal section); 1 1. Ceratophyllum wallichii (root coral) (11a. Cross section,11b. Longitudinal section); 12.Wentzelophyllum (like Brunei coral); 13. saccular coral (foam coral) (13a. Cross section, 13b. Longitudinal section); 14. Peach (slipper coral)
Dog Michelin, 1840 (canine tooth coral) (Figure 2-65438+6, 2006): Monomer, curved cone. The length of the primary partition wall and the secondary partition wall alternate, and the partition wall reaches the center in childhood, and the transverse plate belt thickens in the main part, and becomes shorter in adulthood. The main inner groove is deep and wide. Scales are arranged in herringbone or concentric shape, and the width is uncertain. The transverse plate is complete, convex or horizontal, and the edge part is slightly inclined downward. Carboniferous-Triassic.
Pseudomonas Yu,1931(pseudoula corallina) (Figure 2-65438+7, 06 in total): Monomer, large or medium, curved conical to cylindrical. With the edge foam belt, the foam board first develops on the opposite side, and there are 1 ~ 3 rows of small foam boards on the individual edge. The opposite partition wall is thin and long, often exceeding the center, and the main partition wall is obviously thickened. In the late adolescence, there are obvious internal sulcus. The transverse plate is relatively complete and slightly convex. Early carboniferous.
Dibunophyllum Thomson et Nicholson, 1876 (exfoliated coral) (Figure 2- 16 5): Monosomic, conical-columnar, tri-zonal coral with a large and symmetrical central column, which is equally divided by a long and protruding middle plate. The secondary partition wall is short, and the scales are often herringbone or semicircular. The main internal sulcus is developed, and the longitudinal section is obviously divided into three zones, and the horizontal plate is convex or nearly flat. Carboniferous.
Hexagonaria Gurich, 1896 (Hexagon Coral) (06 Figure 2-65438+8): polygonal complex, with deep calyx pore and obvious outer wall. There are two partitions, the first partition almost reaches the center, and the second partition has an indefinite length, which is generally equivalent to the width of the scale bar. Scales are regular or herringbone. Transverse plates are often divided into central transverse plates and edge inclined plates. Middle and late Devonian.
Fleming in stone, 1828 (shizhu coral) (Figure 2- 16-3): complex polygon or cluster. The next door is long and short, with an obvious central axis. Transverse plates are often tent-shaped, and some transverse plates have small horizontal transverse plates at the edges. Ruler bands are usually narrow. Carboniferous.
Polygonal coral (19 16) (fig. 2- 16, 10): massive complex, with many protrusions on the surrounding wall, and irregular polygons in individual shapes, with the outer wall often partially disappearing, among individuals. The three-zone structure is obvious. There is an obvious "inner wall" at the junction of the separation belt and the foam belt. Complex columns are typical. The edge foam board has large convexity and different sizes. The transverse plate inclines downward towards the center. Early Permian.
Comparison: The genus is very similar to Wentzellophyllum Hudson, 1958 (like Brunei coral) (Figure 2- 16, 12) in individual three-band structure. The main differences are as follows: ① The individual of this genus is irregular, and the outer wall partially disappears, but the outer wall is as complete as Brunei coral. (2) The foam board of this genus has a large crown and a slightly spherical cross section, while the foam board of the latter is dense and numerous, with a small crown. (3) This partition wall generally does not extend into the foam belt, while the starting point of the latter partition wall often extends into the foam belt intermittently.
Liangshan Coral Tseng, 1949 (Liangshan Coral) (06 Figure 2-65438+9): Complex, cylindrical, with narrow edges and thick nodes. The center column is small and consists of a center plate, a spoke plate and an inner inclined plate. The scale band is narrow, with only 1 ~ 2 rows of scales. The transverse plate belt is wide, the transverse plate is nearly horizontal or concave, and the inclined transverse plate is developed. Permian.
Waagenophyllum Hayasaka, 1924 (Wigan coral) (1 1- 16 in Figure 2): complex, clustered. The beginning of the partition wall leads directly to the outer wall, with alternating length. The composite center column consists of spoke plates, inclined plates and middle plates. The transverse plate is narrow, steep and foam-like, inclining downward to the center, with developed scales. Permian.
Cystiphyllum Lonsdale, 1839 (foam coral) (Figure 2- 16, 13): Monomer, with wide cone, trumpet or column, filled with foam board, sometimes with short ridge partition wall, which develops around the individual and is irregularly distributed on the foam board. Silurian Period
Calceola Lamarak, 1799 (slipper coral) (Figure 2- 16, 14): single, slipper-shaped, with deep calyx, semicircular calyx cross-section, semicircular calyx cover, short ridge of septum, protruding to septum, and located in the center of the plane. Except for a few varieties, foam boards are generally not seen. Early and middle devonian.
2. Identification of Common Fossils of Sinocoralline
Chaetetes Waaldeim of Eichwald, 1829 (spiny coral) (Figure 2- 17-3): it is a complex block, consisting of slender polygonal columnar individuals with a diameter of 0. 15 ~ 1.2 mm, and the individuals are close to each other. Ordovician-Permian.
Favosites Lamarck, 18 16 (honeycomb coral) (Figure 2- 17, 1): massive complex, hemispherical, flat or otherwise irregular. The individual is a polygonal cylinder with tight body wall and common middle seam. Connecting holes are distributed on the wall (wall holes) with 1 ~ 6 columns. The transverse plate is complete and thin, generally horizontal or inclined, and the partition wall is rows of wall spines or wall tumors. Silurian-Permian.
Halysites Fischer von Waldheim, 1828 (chain coral) (fig. 2- 17-6): compound chain, consisting of columnar or elliptical columnar individuals. There is a middle tube between individuals with a rectangular cross section. These chains are connected at different angles, and the cross section of the whole coral body is screen-shaped. There are many and neat transverse plates. Next door is sometimes inconspicuous, and sometimes there are several short thorns arranged radially next door. Middle ordovician-SILURIAN.
Syringopora Goldfuss, 1826 (flute coral) (fig. 2- 17 quater): a cluster complex composed of cylindrical individuals connected by connecting pipes. The diameter of the connecting pipe is usually smaller than the individual diameter. The transverse plate is funnel-shaped, sometimes with discontinuous shaft tubes and thin body wall. Are there any thorns next door? Larvae usually grow from connecting tubes. Ordovician-early Permian.
Hayasakaia Lang Smith et Thamas, 1940, Emend Sokolov, 1947 (early plate coral) (fig. 2 17, No.5): a cluster, consisting of straight and curved prismatic individuals, with four rows of regularly distributed connecting tubes at the edge. There are continuous or intermittent foam bands along the edge of the body wall. The transverse plate is complete or incomplete. Early Permian.
Heliolites Dana, 1846 (Sunshot Coral) (fig. 2- 17 bis): a massive complex, usually spherical and sometimes branched, consisting of two kinds of tubes. The large tube is cylindrical, which is the habitat of corals. The partition wall is extremely short, often 12, with transverse plates. The tubule is prismatic, and it is a * * * bone secreted by the * * body. There is no partition wall, and the transverse plate is flat and dense. Late ordovician-middle devonian.
Fig. 2- 17 fossil representatives of Corallinae.
1.Favosites (honeycomb coral) (1a. Cross section,1b. Longitudinal section); 2. actinolite (sun coral) (2a. Cross section, 2b. Longitudinal section); 3. Spiny coral (3a. Cross section, 3b. Longitudinal section); 4. Porphyra syringae (flute coral) (4a. Cross section, 4b. Longitudinal section); 5. Early plate coral (5a. Cross section, 5b. Longitudinal section); 6.Halysites (chain coral) (6a. Cross section, 6b. Longitudinal section)