Through special preservation, we established a phylogenetic connection between the Ediacaran and Cambrian metazoans. We describe the first three-dimensional, pyriteized soft tissue in Namacalathus of the Ediacaran Nama Group in Namibia, which follows a basic form of a stalked, cup-shaped, calcite skeleton with six radially arranged lobes protruding to a tip In the openings and side cavities. There are thick body walls and possible J-shaped intestines in the cup. The usually thorny bones and the middle layer of the bone holes are selectively pyritized to support organic-rich components and possibly sensory points. Tripartite structure. These characteristics indicate the total population lophotrochozoan affinity. These morphological data support molecular phylogeny and prove that the origin of modern lophotrochozoan phylum and its biomineralization ability have deep roots in the Ediacaran period.
Ediacara-Special preservation of Cambrian fossils, approx. From 570 to 500 million years ago (Ma), it provided an in-depth understanding of the first radiation of metazoans. Although the oldest hypothetical skeletal metazoan is known to come from the end of the Ediacaran period, due to the general lack of clear bone characteristics and soft tissue preservation, it is impossible to clearly determine the affinity and therefore the origin of the main metazoan group cannot be understood. Here, we describe the first, three-dimensional, pyrite mineralized preservation of soft tissue in the Ediacaran skeletal metazoan Namacalathus hermanastes from the Nama Formation in Namibia, with new features supporting bilateral, lophotrochozoan affinity. By doing so, we have also established a strong evolutionary link between the late Ediacaran and the early Cambrian taxa.
Namacalathus is a sessile, benthic skeletal creature, widely distributed in various carbonate environments, including clotted rock reefs and shallow lagoons, approx. Before 550 to 540 Ma. Namacalathus has a goblet-shaped skeletal form, formed by a hollow stem that swells from approximately into a calyx. It is 3 to 35 mm in diameter, with a central top opening and 5 to 7, but usually 6 side cavities (1-3). Some individuals have spines on the outer surface of the stem and cup (2), and neighboring individuals are found to have a shared cavity, which is interpreted as representing potential bilateral, asexual, outer buds (3). The current bone mineralogy is usually low-magnesium calcite, but the original mineralogy may be magnesium calcite or aragonite (1,4). Maintaining plastic deformation means that the bone wall is flexible and therefore rich in organic matter (1). The bone microstructure is described as diagenetic, travertine-like cement (5), but the well-preserved specimens show a leaf-like exoskeleton layer and endoskeleton layer, with the middle layer presumably rich in organic matter (3).
Namacalathus is considered a cnidarian because of its six-radial symmetry and cup-shaped morphology, as found in some hydrops, newts and stauromedusae (1). Others have proposed protozoan affinity because there is no proliferative growth (6) or total lophorate based on leaf-like bone microstructure and bilateral budding (3). Recently, based on phylogenetic analysis and general morphological similarity with sessile, Cambrian skeletonized “dinomischids” and hardcore fishes, stem group ctenopsis mothers and sex have been proposed (7).
Here, we report the unusually well-preserved Namacalathus individuals found in the uppermost Omkyk member of the Nama Group in Namibia. They come from a low-energy, very shallow, carbonate-dominated internal slope environment, which was 547.32 ± in one era. Below the 0.65 Ma gray layer (see Figure S1) (8). Individuals of Namacalathus range from 4 mm to 12 mm in diameter, although many are partially covered by sediments and preserved as reddish brown to yellow (hydroxy) oxide minerals, FeOx ["FeOx" here means unspecified iron oxide (hydroxy) ] Pyrite (FeS2), or as raised gray limestone castings, sometimes shows the weathered part through a calcified skeleton (Figure 1 and Figures S2A and S3). 73 individuals (numbered 1 to 73) were found on a flat sample of bedding, some of them with stems (Figure S2, A and D), 29% of them remained upright in the inferred growth position, 48% fell slightly, 23% undecided direction (Figure S3). The host lithology is a fine layered micrite graded from mud-rich marl, with some silt-grade quartz and recrystallized biological debris, usually in contact with columnar bodies (Figure S2C). The individual Namacalathus was immediately covered by thin (<1 mm) micrite carbonate, which contained silt-grade horn-like debris fragments of quartz, albite, clay, and phosphate minerals (Figures S4 and S5).
Museum number F1547, Geological Survey Museum of Namibia. For numbered individuals, please refer to the diagram. S2A. Scale bar, 2 mm. (A to D) The upright Namacalathus cup shows the central opening (CO) and the fold (white arrow). There are ridges (R) and domes (D) around the CO, with pincushion lobes (Lo) and iron oxide staining (FeOx) of the sediments surrounding the fossils. (B) Folds (arrows) around CO and related D. (C) Illustration of (B) showing the radiation D (black arrow) and folds (white arrow) around the CO. (D) Front view showing the fold (white arrow)) around the central CO and lumen (L), with opposite folds (black arrow). (E) The casting is preserved, CO and the top of the three L have a calcite skeleton (black arrow). Deposits between lumens stained with FeOx (brown arrows). (F) CO and L are stored in FeOx with a calcite skeleton (black arrow) underneath. (G) Collapsed Namacalathus cup with R and D around L. (H) Illustration (G), showing the dome and ridge (black arrow) around L. Barbed (Sp).
The best-preserved individual exhibits a raised pincushion-like shape that surrounds the central and top openings. The diameter of the center top opening ranges from 1.3 to 12.3 mm (n = 37, average = 3.6 mm), can be circular (Figure 1, E and F, and Figure S3, K to N) or show 5 to 7, But there are usually six iso-oblique folds radiating outward (Figure 1, A to D and F, and Figure S3, A to J, P, and Q). The folded height ranges from 0.18 to 2.78 mm, and the width ranges from 0.43 to 4.66 mm (Table S1). Both types of openings are preserved as FeOx crust (Figure 1, A to D and F, and Figure S3, A to G and M to Q) or limestone castings (Figure 1, E and I, and Figure S3, H to L And W to X). In the cup where the central opening and the lumen are visible, the central opening fold is opposite to the fold across the lumen (Figure 1D). The complete lumen is similarly observed as FeOx crusts (Figure 1, G and H, and Figure S3, P to U) or castings (Figure 1I and Figure S3, V to Y). Compared with limestone castings (average = 2.34 mm), the lumen height (average = 1.59 mm) preserved by FeOx is smaller, but the preservation method does not significantly affect the width of the lumen (average = 1.8 mm; Figure S6B) . There are small (0.33 to 1.27 mm; Table S2), dome-shaped or elongated ridge-like swelling around the edge of the central opening and lumen (Figure 1, A to C, G and H, and Figure S7), concentrated in The fold apex around the top opening (Figure 1A and Figure S3, A and C, and S8, A and B) or parallel to the lumen edge in a specimen (Figure 1, G and H, and Figure S3R and S7, C and D), or in pairs radiating from the apical opening to the lumen (Figure 1, B and C, and Figure S3, C, D, and P). The calcite skeleton is also preserved (Figures 1, E, F, and J, and Figures S3, Q, Z, and Aii to Av), showing a solid radiation spur with a length and width of 0.4 mm, in which the FeOx crust has not been preserved (Figure 1J and Figure S3, Z to Av).
X-ray micro-computed tomography (μCT) imaging of two individuals (numbers 4 and 32) showed that pyrite mineralization showed the presence of soft tissue and a cup-shaped calcite skeleton, with no stems below the plane surface of the cushion (Figure 2). 2 and Figure S8). Visual inspection of the fossil (Figure 1) and μCT image both showed that the uppermost soft tissue appeared as six radially arranged leaves, separated by folds protruding to the central opening and the top of the lumen (Figure 2). A cluster of large spirally coiled bacteria, possibly Obruchevella, mainly from Neoproterozoic and Cambrian sequences (9), was also selectively mineralized by pyrite outside the Namacalathus cup (Figure 2, C, F to H and K to M).
Museum number F1547, Geological Survey Museum of Namibia. (A) to (D), (F) to (I) and (K) to (N), none. 32, and (E), (J), and (O), no. Figure 4 shows the CO surrounded by FeOx (green-blue), showing Lo, L, and folds (yellow arrows). The calcite skeleton (CS; blue) remains below the bedding surface, outlines L. CT, central tube; scale bar, 2 mm. (A) Plan view of Namacalathus cup. (B) False-color μCT section of the core (C to C’of A). (C, F to H, K to M) Reconstruction of the Namacalathus cup rotating from the central axis. Oh, the big bacteria, it may be Obruchevella. (D, I, and N) Photomicrographs of the continuous longitudinal surface during serial sectioning (A and A’, B and B’, and D and D’of A), the arrow traces the film on the CO. (E, J, and O) A three-dimensional model rendered with gray-scale CT cross-sections, highlighting Lo, CS, and CT. Sp, spine; P, pore; CT, central structure; Fl, flange; white arrow, iron oxide concentration in the cup; blue arrow, upward.
Serial slices polished by Namacalathus (No. 32) confirmed the existence of an internal calcite skeleton with selective pyrite mineralization. The overlying soft tissue leaves are preserved by framoidal pyrite, most of which are oxidized to FeOx, so Called FeOx framboids here are pseudomorphs after pyrite (Figure 2, D, I, and N and 3, and Figures S9 and S10). The backscatter scanning electron microscope (SEM) image also distinguishes between the calcite framework of selective pyrite mineralization and the fragments that are completely preserved by pyrite mineralization (Figure 3A and Figures S11 and S12). There is a horizontal calcite skeleton flange extending 950 μm from the central opening (Figures 2N, 3A, and 4C), and its straight side is close to the pyrite shards, as shown by the cathodoluminescence (CL) imaging (Figure 4D) . FeOx staining up to 0.5 mm thick is also evident in the cup near the inner wall (Figure 2, D, I and N; 3A; and 4B), extending into the lumen (Figure 2N and Figure S10), B and C) , And plaques up to 0.1 mm thick on the outer wall (Figure 2I). There are thin FeOx-rich channels 50 to 300 μm wide, which extend vertically through the entire wall thickness, usually through the central part of the spines (Figure 3, A, E, and F, and 4, E, and F). The slit is also parallel to the bone wall (Figure 4H), or between the spinous processes (Figure 4I), and may bifurcate (Figure 4I). These slits extend to a depth of at least 450 μm (Figures S10 and S13). FeOx staining is evident on the outer and inner walls of the channel termination (Figure 2, D, I, and N; 3, E, and F; and 4, E, and G to I). CL imaging shows that the skeleton is composed of poorly partitioned, mainly dark-emitting, massive new-shaped crystalline calcite (Figure 4, F and R), in which crystals of different orientations exist on both sides of the pyrite mineralization pore (Figure 4F).
Museum number F1547, Geological Survey Museum of Namibia. (A) to (F), no. 32. Slice D and D’(Figure 2N). (G) to (J), no. 68. (A) Scanning electron microscope (SEM) images show CS and Fl and L, pyrite/FeOx leaf soft tissue (FeOx) and CT, and S. (B) Inset (A), the soft tissue leaf of Namacalathus is on the bedding surface filled with FeOx framboids (Fr). (C) Illustration of (B) showing FeOx Fr. (D) The illustration of (A) shows the FeOx Fr wire (shown by the arrow) passing through the CO, which is connected to the CT. (E) The illustration of (A) with a spine filled with vertical holes of FeOx Fr. (F) Illustration of (E) showing FeOx Fr. (G) FeOx Fr in the central area of the frame and CT. The illustrations of (H) (G) show that the middle layer of FeOx Fr (FeOx) in CS expands toward the bedding surface, and S2 spherical deposits and FeOx (shown by the arrow) partially replace the spheroids (P). SC, buried calcite. (I) Illustration of (G), FeOx cement around S3 calcite and debris particles. (J) Illustration (G), FeOx Fr in CS.
Museum number F1547, Namibia Geological Survey Museum, number. 32. The longitudinal section highlights the characteristics of CS and FeOx. (A) Parts D and D’(Figure 2N) and (B) Parts B and B’(Figure 2I) show the highlighted areas. (C and D) Fl covered by CS and FeOx (contact arrow). (E) Hole (arrow) along Sp. (F) FeOx small frame is lined with holes (F) (yellow arrows), forming grain boundaries (white arrows). (G) The pores filled with FeOx framboids (shown by the arrow) and the cross section of the central tubular structure (CT, boxed). (H) CS and FeOx staining parallel (white arrow) and exoskeleton wall (yellow arrow). FeOx is concentrated where the channel penetrates the outer wall of the cup (red arrow). (I) Channels with bifurcations (blue arrows) and FeOx (white arrows) in the area between the spines. The concentrated FeOx is located on the outer wall and where the channel penetrates the inner wall of the cup (red arrow). (J) The leaves are surrounded by FeOx stain (shown by the arrow) and connected to the CT (boxed). (K) FeOx dyeing is consistent with bright luminous calcite. (L and M) CTS section in (G) and (J) with calcite (white arrow) surrounding F (yellow arrow). (N and O) The FeOx staining of the film (shown by the arrow) is consistent with the brighter luminescence (shown by the arrow), connected to the CT. (P) Illustration (O), CT and calcite (C) and center F (yellow arrow). (Q and R) CS; Lumens (L), there are S1 and S2 deposits outside and inside the cup, respectively.
A tubular structure was found within three-quarters of the area, usually composed of a central area of framboidal FeOx and an unzoned, dimly glowing, crystal-clear calcite (also used as a late cement filler in carbonate sediments) Existence) defines that Namacalathus cups are analyzed and can be distinguished in polished serial sections, as well as imaging by CL and backscatter SEM (Figure 2, D, I, and N; 3, A, and D; and 4, L, and M ; And Figures S4, S9, S13 and S14) and μCT (Figure 2, E, G, H, J to M and O). This structure has an elliptical cross-section with a diameter of up to 400 μm and can be connected to a 100 to 400 μm thick FeOx thin layer covering the central opening of the cup (Figure 2, D, I and N; 3D; and 4, N And O). Then the tube descends into the cup, moves to the inner wall, expands to a circular cross-section of up to 600μm, and then bends in the cup to form a J-shaped structure (Figure 2, E, J and O), sometimes the width is reduced to the end and disappears without adhesion (Figure S12).
FeOx framboids are abundant in soft tissues (Figure 3C and Figures S11 and S12) and bones (Figure 3J and Figures S5 and S12). There are no leaflets in the wider sediments. The newly deformed sparry calcite skeleton of Namacalathus also contains a large amount of FeOx framboids. These usually occur in the well-defined straight-edge middle layer (Figure 3G), where the pyrite mineralization extends almost to the entire width of the uppermost skeleton of the cup, thinning toward the bottom of the cup, where the calcified outer and inner bone layers thicken (Figure 3, G and H). The thin accumulation of FeOx framboids also occurs in patches along the inner and outer bone surfaces, and in addition, an inverted V shape is selected in the calcite part of the bone (Figure 3, G and J). CL imaging shows the partitioned calcite cement growing around the uncompacted sediment, projecting into the new calcite framework of Namacalathus and other new-form bioclastic particles (Figure 4F). The main bright CL bands of the partitioned calcite cement growing around the uncompacted sediments are consistent with the FeOx staining visible near the upper part of the cup (Figure 4, C and D), and also consistent with the FeOx thin layer passing through the central opening (Figure 4 And Figure 4). 2. D, I and N, and 4, N and O). The SEM image of this area confirmed the presence of a framboidal FeOx line (Figure 3D).
Spheroids are abundant in areas with visible iron staining, where the spheroids are partially replaced by pyrite/FeOx (Figure 3H). Similarly, the bed surface sediment particles above the Namacalathus instance are covered by pyrite/FeOx cement (Figure 3I). Therefore, CL imaging revealed three types of carbonate sediments associated with the Namacalathus cup (Figure 3C)-bioclastic-rich sediments fill the bottom of the cup (S1), spheroid-rich sediments, and upper part Partial pyrite/FeOx replacement. The cup (S2), and the debris-rich sediment (S3) overlying with pyrite/FeOx cement (Figure 3, H and I and 4R).
Therefore, we infer that the early precipitation of pyrite and calcite cements is the cause of this special three-dimensional preservation (10). This type of preservation occurs in a sulfate reduction environment, which has a high concentration of highly active iron, but the availability of organic carbon in early diagenesis is very low or very local, where pyrite precipitation is only related to unstable tissue Related, the cell structure is destroyed (10) and the form of pyrite there may reflect the relative sensitivity of the original material to decay (11,12). Under these conditions, small pyrite spheroids may form on the organic matter within a few hours to a few days (13). We infer that dendritic pyrite formed very early and replaced the organic-rich parts of soft tissues and presumably bones. The appearance of the pyrite mineralizing bacteria discovered together with Namacalathus is very rare in the fossil record and confirms that the rate of pyrite mineralization is sufficient to replicate soft tissues.
The bright CL band of the early calcite cement is associated with the sediment in the upper part (S2) of the cup, indicating high manganese and low iron pore water conditions (Figure S4). S2 sediments are also characterized by FeOx staining, which is presumably derived from the oxidation of pyrite. This confirms the coincidence of the cementation of early pyrite and early calcite. It is known that the formation of early carbonate cements is promoted by the degradation of cell walls, extracellular polymers, organic matter degradation, and other metabolic or microbial processes that may form spheroids [e.g., (14)]. The local dissolution around the soft tissue of the pyrite may be caused by the limited oxidation of the pyrite, leading to the formation of a mold, which was later filled with buried calcite spar cement.
At the end of the Ediacaran Gaojiashan section of the Dengying Formation in China (15), the Chengjiang and Guanshan Lagerstätten of the Early Cambrian in China (11), the Fenxiang Formation of the Lower Ordovician (16), the similar three-dimensional preservation of soft tissues in the pyrite, and the lower The Cretaceous Santana formation (12) is usually formed by the rapid burial of storms. In the Nama group, the proximal, very shallow, low-energy environment provides a fine-grained medium and sufficient calcium carbonate saturation to promote early cementation. Individuals of Namacalathus may also be quickly buried by thin intrusion of terrestrial lithic-rich sediments in their lives, and the folds of the central top opening may represent a state of contraction. Folding is unlikely to be buried, because the number of folds seems to be related to the number of lumens (Figure 1D). Cloudinids in a bed dominated by siliceous clastic rocks in the Wood Canyon Formation in Nevada show more spatially confined framboidal pyrite mineralization, retaining the cylindrical internal structure of the digestive tract that was recently explained as possible (17). The internal digestive tissue is completely unknown in the Ediacaran record, although it is common in the Cambrian Ragstatten (17). All in all, the process operating in this protected environment creates a unique Lagerstätte.
The middle layer rich in pyrite in the Namacalathus framework confirmed the existence of a tripartite framework with a central part rich in organic matter (3). FeOx framboids in thin layers in other parts of the framework also indicate the presence of a thin organic-rich layer, parallel to the potential line of growth. The additional presence of small calcite penetrating the wall and new-shaped calcite in different directions on both sides of the pores indicate that these are the main biological features, such as pores penetrating the wall and longer channels penetrating spines. The thickness of the middle layer of pyrite increases toward the upper part of the skeletal cup, indicating that this may be the initial bone formation area in contact with other soft tissues. This middle layer may have formed an organic template on which the outer and inner calcareous layers are formed, and therefore are areas where bones are actively growing, as observed in modern corals and long-stalked corals [e.g., (18) ]. FeOx staining is widely observed in thinner plaques inside and outside the cup and in the lumen, indicating the presence of soft tissue.
To sum up, Namacalathus has a cup-shaped calcareous skeleton, hollow shank, open center, generally six radial symmetry, large cavities on the side, leaf-like microstructure, uniform columnar curvature, rich organic layer in the middle, and asexual on both sides Reproduction. Budding (1,3). The soft tissues faithfully follow the internal bones, and the lumen does not have the previously suggested local, diagenetic, and lytic origin (1). In addition, we noticed the formation of folds between the radially arranged lobes, which extend from the central top opening to the side cavities, organic-rich holes and channels in the bone wall; internal, asymmetric, J-shaped tubular structure , The soft tissue adheres to the inner wall of the bone; the inner membrane next to the central opening; and the thin outer layer rich in organic matter. The tubular structure is present in multiple specimens and is clearly connected to the membrane of the transoral opening, indicating that it has a feeding function. Or, this may represent a retraction of the muscle band, but it is more likely an extension of the intestine or body cavity, possibly a partially retained U-shaped intestine. We note that this presumed framboidal pyrite preservation of the intestine is similar to the soft tissue structure of the intestine in the cloud recently interpreted as the Wood Canyon Formation in Nevada (17). The small ridges and domes associated with the central opening and lumen may represent the base of the tentacles; alternatively, they may be formed by the weathering process of pyrite.
The pores or dots may be homologous to similar sized pores or dots in brachiopods, extinct peaches, and microshells, and false dots in bryozoans, which contain bristles and other sensory structures (19-21). Punctae and channels connect thin outer and thick inner FeOx-rich layers, allowing interpretation as mucopolysaccharide-protein periosteum and body wall, respectively. The periosteum has a leaf-like pattern around the central opening, and these leaves can represent the recesses where the tentacles are retracted. The variable contraction and scallop shape of the central opening infer the presence of radially arranged parietal diaphragm dilators. In some bryophytes, the contraction of these muscles pulls the frontal membrane of the polyp inward, extending the tentacles (19). The thin organic structure passing through the top opening of Namacalathus (Figure 2, D, I and N) can be interpreted as the frontal membrane, so the position of the intestine assumed below will correspond to the body cavity conforming to the lohophorate model. Contraction can also be inferred in Namacalathus Mechanism in which muscle bundles may connect the frontal membrane and body wall (Figure 2, D, I, and N).
This set of features, as well as those seen in other specimens [bilateral budding and columnar curvature in the skeletal plate (3)], exclude Namacalathus’ allocation of protists, coralline algae, foraminifera, cnidaria, and comb jelly ( Table S3). Although the six-radial symmetry may be beneficial to the affinity within the cnidarian, some extinct Paleozoic corals have leaf-like microstructures (22), skeletal column points, channels, J-shaped or U-shaped inferred intestines and frontal membranes instead of The large, central, pharynx, and lack of mesenteric structures do not support the affinity of cnidarians.
The skeletal representatives of Lophophorata, including the stem and crown group of brachiopods, bryozoans, and extinct micro-conchs, have very similar leaf-like microstructures with columnar curvatures that extend to the spines. The consensus tree of 54 lophotrochozoan taxa in which Namacalathus occupies a basic position indicates that this “tubule” microstructure and “dots” have multiple origins in the entire brachial group (23). The absence of any traces of the stomach cavity and the discovery of small spots and channels that may be rich in organic matter in the bone wall further emphasizes the sensation observed in long-handed animals (brachiopods, docktails, and micro-conchs). The similarity of porosity (21,24), such as whether there is a possible J-shaped or U-shaped intestine. Usually six large lateral cavities point to the colony tissues of Namacalathus or individual organisms, where the cavities may correspond to the brooding chamber formed by the invagination of the external body wall, as found in bryozoans (19). Invasion of the body wall was observed in the lumen of Namacalathus (Figure S10, B and C).
The identification of the caterpillar fauna in the Ediacaran was supported by molecular phylogeny (25) and had an impact on the evolution of the earliest nematodes. Since the early Cambrian, the biomineralized stem group lophotrochozoans has a rich fossil record, in which the possession of calcareous bones or external hard bones may represent bones with variable mineralogy in the benthic fossil taxa that have independently obtained sessile attachments. These bones have characteristics shared with Namacalathus. These include tommotiids (26) and hyoliths, which are peduncle and tentacle creatures lacking lopophore (23). Some cup-shaped Cambrian forms similar to Namacalathus, such as Cotyledion tylodes from the Chengjiang deposit, may represent Dinoflagellates. It also shows an upper calyx and a slender stem. The central tube is interpreted as an extension of the calyx cavity in a U-shaped band. An intestine with a mouth and an anus surrounded by retractable edge tentacles, and the outer surface is covered with external hard bones that may have been mineralized (27).
Cotyledion and some other Cambrian long handle fossils, namely Dinomischus and Siphusauctum, have been compared with entoprocts (27-29). These fossils are relatively large (over 15 mm in height), while the existing entoprocts are very small (less than 1 mm) and not biomineralized.
Entoprocta is a mysterious monophyletic group of cavityless animals, occupying the basic position of phylogeny among proximal molluscs, close to molluscs (30). Namacalathus has some notable similarities with entoprocts, including the overall shape of the cup (the body is divided into different stems and calyx), hexagonal symmetry, the position of the mouth and anus within the presumed tentacle collar, and the appearance from the forehead area The bilateral buds are personal to the parents. Therefore, we are now able to reconstruct Namacalathus as a whole lophotrochozoan, capable of asexual sprouting, with organic-rich leaf-like calcium bones and an open, top J-shaped or U-shaped gastric cavity, located in the top opening, which may contain The tentacles of the retractable collar and the brooding room surrounding the lumen (Figure 5).
The existing lophotrochozoan phylum sessile, such as annelids, mollusks, brachiopods, and phoronids, have been thought to have originated from the earliest Cambrian small skeletal fauna [e.g., (26)], and they are a sign of the Cambrian outbreak Sexual representation. However, now we can extend the origin of these modern lophotrochozoan gates further to the end of the Ediacaran period. By doing so, we established a phylogenetic link between the Ediacaran and Early Cambrian taxa, which were previously thought to be different. Therefore, we extend the origin of the Cambrian eruption itself to the Ediacaran period, where general lophotrochozoans such as Namacalathus showed a combination of characteristics that became later lophophorates and entoproctan-molluscan-annelidan Typical characteristics of the representative of the branch.
A floating sample (237 mm x 194 mm x 33 mm) was collected from the Zwartmodder farm. A single-lens reflex camera and binocular microscope are used to shoot and record each Namacalathus, and ImageJ software is used to quantify dimensions, such as lumen width and height.
Radiograph the floating sample to determine whether a single Namacalathus cup has a density contrast with the surrounding sediment. Due to the high contrast, Namacalathus does not. 32 was cored and received a μCT scan. The scanning voltage was 120 kV, 1500 projections (average 2 × 2 s exposure) were collected, and 824 tomographic slices were reconstructed by filtering back projections. The contrast is enhanced by applying the stretch histogram option in ImageJ without affecting the original data. Use Avizo 9 software to render the scanned 3D model. The reconstructed voxel size is equal to 20.7 μm. The predefined color map “physics.icol” is applied to the model to help visualize the fossil features, but the false color is not quantitatively related to any properties of the object. The color threshold of the color map was changed in Avizo (255-65535) to remove the background of surrounding calcium carbonate deposits to generate a model of the entire individual. Scan the Namacalathus cup number. The voltage in Figure 4 was also 120 kV, and 633 tomographic slices were reconstructed using the same data acquisition parameters. The model was rendered using Avizo 9 with a voxel size of 23 μm and a predefined colormap “greyscale.icol” because the low contrast of the scan is not suitable for rendering in false colors.
Namacalathus did not. Then cut Figure 32 into three parts to observe the internal structure of the Namacalathus cup (Figure S9). These sections were finely polished and imaged using a binocular microscope and CL (Figure S10). One of the sections was continuously sectioned in 26 micron increments, and was also imaged by a binocular microscope and CL.
Two highly polished flakes are made from slabs to describe the lithology using a petrographic microscope. Three highly polished, uncovered thick sections (200 to 2000 microns) were cut from the cross-section of Namacalathus no. 68 Used for backscattered electron imaging and EDX analysis.
Two samples (No. 66 and 68) were continuously sliced and highly polished in increments of 1 mm and 500 microns, respectively, to understand the distribution of iron oxide and its relationship with the calcite skeleton using optical microscope and CL imaging. Continuously slice at 1 mm of the core plug containing Namacalathus no. 66 allows us to observe the relationship between iron oxide and the calcite framework. Use the CanoScan LiDE 210 flatbed scanner to scan each section (4000 dots per inch for both sections).
Supplementary materials for this article are available at http://advances.sciencemag.org/cgi/content/full/7/1/eabf2933/DC1
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The first evidence of Namacalathus soft tissue established a phylogenetic link between Ediacaran and Cambrian metazoans.
The first evidence of Namacalathus soft tissue established a phylogenetic link between Ediacaran and Cambrian metazoans.
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Post time: Aug-23-2021
