The terminal Ediacaran Tongshan Lagerstätte from South China

Domain: earth_science
Published: 2025-11-19
Editorial outcome: major_revision

Abstract
Because the informative Burgess Shale-type preservation is uncommon in the Ediacaran, mouldic Ediacara-type preservation provides insight into the early evolution of organisms like metazoans (including typical fronds), protists, and algae. Here, we report the Burgess Shale-type preservation from the new Tongshan Lagerstätte (~551–543.74±0.87 Ma), in carbonaceous mudstones/shales of the terminal Ediacaran Dengying Formation in Tongshan, Hubei, South China. The preservation of a high diversity of organisms indicates rapid, likely in situ burial in the marine photic zone below the storm wave base, revealing deep-water biodiversity coeval with the Nama Assemblage of Ediacara Biota. These are the first records, to our knowledge, of typical Ediacaran rangeomorph fronds with Burgess Shale-type preservation. The presence of Burgess Shale-type preservation of fronds reflects the rarity of fine-grained deposits in the Ediacaran Period and bridges an important gap between traditional Ediacara-type preservation, Ediacara-type preservation with organic remains, and Burgess Shale-type preservation.

Introduction
Much of our understanding of the Cambrian radiation, with the abrupt appearances of diverse metazoan genera, reflects the global distribution of fossil Lagerstätten in fine-grained deposits with Burgess Shale-type (BST) preservation1–5. This preservation type records compositional information in both chemical and morphological aspects of organic integuments such as cuticle details6,7 and internal soft tissues such as muscles, gut systems, and nervous systems8–11, in addition to hard exoskeletons. Other early metazoans occur in the Ediacara Biota of the late Ediacaran Period (~575–538.8 Ma), with the first appearance and diversification of macroscopic, multicellular and complex organisms12–19. Our understanding of these organisms is largely dependent on fossil Lagerstätten18, and limited by the depositional environment and preservational mode of each deposit. Unlike Cambrian Lagerstätten with BST preservation, the Ediacara Biota features Ediacara-type preservation that preserves the outline of structures, but the compositional information in both chemical and morphological aspects is unavailable20. Extensive studies on the preservation of soft-bodied fossils have indicated that different styles of preservation, such as Ediacara-type, BST, and pyritization, bias our understanding of the early evolution of animals21–25.

In this work, we document a new Lagerstätte from the terminal Ediacaran Dengying Formation in Tongshan County, Hubei, China. It exhibits a high diversity of organisms, including typical Ediacaran rangeomorph fronds, preserved within a short interval of carbonaceous mudstones/shales at the top of this formation. Its BST preservation type makes compositional information widely available to the Ediacaran metazoans, such as fronds.

Results
Locality of the Tongshan Lagerstätte
Abundant macrofossils were collected from the upper carbonaceous mudstones/shales of the siliceous rocks of the Dengying Formation at the Jiweijian and Wanjia sections in Tongshan County, Hubei Province, South China (Fig. 1a, b). The macrofossils are predominantly preserved with BST preservation. A stratigraphic horizon containing macrofossil Shaanxilithes occurs 18 meters above the Tongshan Lagerstätte at the Wanjia section and is also present at the Jiweijan, Gaojiashan and Zhelinziwan sections (Supplementary Figs. 1a–e, 2). A volcanic ash layer ~4.8 m above the Shaanxilithes zone at the Jiweijian section (Supplementary Fig. 1e) has produced a weighted mean 206Pb/238U zircon date of 543.74±0.87 Ma (Fig. 1d, Supplementary Figs. 1e and 3) by the high-precision chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) of this study. The latter date establishes, by correlation, a minimum age constraint for the Tongshan Lagerstätte, as well as for the Shibantan and Jiangchuan Lagerstätten (Fig. 1c, Supplementary Fig. 1). An ash layer from the uppermost Miaohe Member of the underlying Doushantuo Formation in the Yangtze Gorge area (Jiuqunao section) was dated at 551.1±0.7 Ma by the CA-ID-TIMS method26,27, which, by correlation to the Wuhe section, places a maximum age constraint on the Shibantan Lagerstätte. Similarly, the Tongshan Lagerstätte can be bracketed in age between ca. 551 Ma and 543.74±0.87 Ma. The Tongshan Lagerstätte becomes age-equivalent to the early phase of the Nama Assemblage of the Ediacara Biota28, an interval marking the earliest diversification of biomineralized metazoans29.

Organisms of the Tongshan Lagerstätte
Macroalgae are the main component of the Tongshan Lagerstätte with seven known taxa: Baculiphyca taeniata (Fig. 2a, Supplementary Fig. 4a–c), Chuaria sp. (Fig. 2g), Doushantuophyton lineare (Fig. 2c), ? Gesinella hunanensis (Supplementary Fig. 4d), Longifuniculum dissolutum (Fig. 2j), possible Tawuia (Supplementary Fig. 4e), and Zhongbaodaophyton robustus (Fig. 2b). Five undescribed forms have been discovered: a Doushantuophyton-like form (Fig. 2d), a baseball bat-like form with an expanded distal end (Fig. 2e), an irregular circular form (Fig. 2f) with bounded filaments, a net-like form (Fig. 2i) with crossing filaments, and a ribbon-like form (Fig. 2k) with bounded filaments. The undescribed filamentous macroalgae (Fig. 2d, f, i, k) are larger than previously known taxa, other than the erect, skinny Doushantuophyton. Beltanelliformis brunsae, with a possible microbial origin (Fig. 2h, Supplementary Fig. 5a–d), and the enigmatic Palaeopascichnus linearis (Fig. 3c, Supplementary Fig. 6a), are also present. Four putative metazoans include three known species, Protoconites minor (Fig. 3a), Sinospongia chenjunyuani (Supplementary Fig. 6b–c), Eoandromeda octobrachiata (Fig. 3d), and one undefined tubular form with segment-like divisions (Fig. 3b). This youngest report of Eoandromeda extends its occurrence from the White Sea Assemblage to the Nama Assemblage, suggesting the previously known disappearance of octoradialomorphs near 551 Ma30 is a taphonomic artifact or sampling bias. A tubular structure (Fig. 3b) showing segment-like divisions and its distal portion showing an irregular opening at the top may be related to either cnidarians or annelids by comparison to tubular cloudinomorphs.

Typical frondose organisms discovered in the Tongshan Lagerstätte, including Rangeomorpha clade31, have been phylogenetically linked with metazoans13,17,19,32,33. The specimen ESEN0016, with a distally tapering end that curves to the upper right side, is clearly divided longitudinally into three distinct lobe-like regions: a slightly wider central region and two lateral regions (Fig. 4a, c). The two lateral regions represent two individual petaloids, each composed of dozens of the first-order branches arranged parallel to one another (Fig. 4b, d). The second-order branches, visible under low-angle lighting, are almost perpendicular or slightly inclined relative to the first-order branches (Fig. 4b). The central region contains the stalk; however, this region likely includes a few overlapping petaloids, which are difficult to distinguish due to compression. The overlapping stalk and petaloids are more distinct at the proximal part of the specimen, where two lateral petaloids are arranged in parallel along the long axis of the central stalk. The total body construction and the presence of the first- and second-order branches indicate this specimen is a typical rangeomorph metazoan.

Ten fan- and bush-like specimens are similar to Bradgatia (Fig. 5a, b). Segments of branches are clearly visible and show 3D in morphology (Fig. 5d–f). The fan-like shape with V form (Fig. 5a) is comparable to the early growth stage of Bradgatia34. The possible elliptical holdfast at the proximal end of the bush-like form (Fig. 5b, c) provides evidence that the attachment style is comparable to the holdfasts of other typical Ediacara fronds. Ontogenetically Bradgatia changes from forms I to V to U and to O24, the two forms (Fig. 4a, b) become comparable to the intermediate growth stages (V and U) of Bradgatia. All evidence indicates they are rangeomorphs.

Dozens of specimens, such as ESEN 0019 (Fig. 5g–h) have a spherocylindrical outline with a blunt distal end are comparable to rangeomorphs such as Charniodiscus based on broad morphology. The elliptical holdfast may reflect lateral compression during preservation. The width of the petalodium is equal to the diameter of the holdfast. Contrary to one petaloid on the left side, the two almost parallel longitudinal curves on the right side are likely an impression of the margins of two individual petaloids. The first-order branches are parallel to one another (Fig. 5i), while the second-order branches are perpendicular to or inclined relative to the first-order branches (Fig. 5j–k). Some annulation-like divisions on the second-order branches may represent the potential third-order branches (Fig. 5j–k). A circular spot, defined by a faint white margin at the center of the holdfast, represents the stem or stalk of the petalodium (Fig. 5h). As the petalodium and holdfast were compressed during preservation, whether a stem is present remains unclear. However, if a stem was originally present, the stem must have been short.

Another form with five specimens has the widest portion located on the lower part of its fusiform body (ESEN0020; Fig. 6a–d). This form has a long tail-like distal end that is similar to Paracharnia. The first-order branches are parallel to each other (Fig. 6a–d) and some second-order branches (Fig. 6c) are distinct near the proximal portion of some primary branches. At the middle portion, the first-order branches of the petaloid meet at the mid-line (Fig. 6a–b). On the right side, a few parallel curves may represent the margins of several superimposed individual petaloids (Fig. 6b). Petaloid branches are clearly visible on both sides even if the whole body is slightly twisted. The proximal, elliptical end represents the holdfast because it stands out from the stalk region at the upper left corner. All these characters indicate it is a typical rangeomorph.

One specimen has a blunt conical outline, with one petaloid on the left side and possibly two superimposed petaloids on the right side (ESEN0021; Fig. 6e–g). Parallel segments of petaloids are clearly recognizable on the upper part of the specimen. A possible holdfast with a faint outline is preserved with a diameter about half of the maximal petalodium diameter (Fig. 6g). A circular spot located at the center of the possible holdfast represents the stem or stalk of the petalodium (Fig. 6g). These characters indicate it is a typical frondose organism.

EDS analyses of two frond specimens, ESEN0017 and ESEN0019a, display high concentrations of C and Fe in the body fossils, which contrast with the high concentrations of Mg, Al, K, Ti, and Ba in the matrix (Table 1, Supplementary Fig. 7). In both specimens, Si and O exhibit similar concentrations in both the fossil body and the matrix. Specimen ESEN 0017 (Supplementary Fig. 7a) has a higher concentration of S in the fossil body, whereas specimen ESEN 0019a (Supplementary Fig. 7l) has a higher concentration of P (Table 1, Supplementary Fig. 7).

Methods
Fieldwork
We acquired permission from the landowner for conducting scientific research. The late Ediacaran Dengying Formation is consistently and widely distributed in the Tongshan County and adjacent areas. The first fossil was discovered at the Jiweijian section, which is also where tuff sample was dated. After extensive exploration, we selected the Wanjia and Jiweijian sections, Tongshan County, Hubei, China, for detailed study. Fossils were collected and carefully packed in the field and transported to the School of Earth Sciences and Engineering at Nanjing University between summer 2022 and spring 2025.

Dengying Formation in Tongshan County, Hubei
Ediacaran strata in Hubei Province of South China are stratigraphically and palaeogeographically divided into the Yichang-Tongshan and Yunxian-Yingshan regions, of which the Yichang-Tongshan region is further subdivided into large Huangling-Dahongshan and small Hefeng-Tongshan areas71. Extensive studies have been carried out in the Huangling-Dahongshan area72–74, but little work has focused on the Hefeng-Tongshan area. The Dengying Formation in the Hefeng-Tongshan area is divided into two parts; the lower limestones are 74.08 m thick, whereas the upper siliceous rocks are 224.75 m thick71 (Supplementary Fig. 1c). This is in contrast to the adjacent Huangling-Dahongshan area, including the Yichang and Three Gorge Area, where the Dengying Formation is subdivided into the Hamajing, Shibantan, and Baimatuo Members in ascending order (Supplementary Fig. 1b)73. Lower limestones of the Dengying Formation in Tongshan County are dominated by limestones and dolostones (Supplementary Fig. 1c). Upper siliceous rocks of the Dengying Formation have the basal part dominated by limestones and dolostones and the upper part composed of four lithological units: dark carbonaceous mudstones, thin- to medium-thick gray bedded cherts, dark gray carbonaceous mudstones, and thin- to medium-thick bedded cherts, in ascending order71 (Fig. 1d, Supplementary Fig. 1c). Our materials were yielded from and through upper carbonaceous mudstones/shales at the Jiweijian and Wanjia sections of the Tongshan County (Fig. 1a, b, d, Supplementary Fig. 1c–e), about 350 km away from the Three George Area where the Miaohe and Shibantan Biotas were discovered42,73. The fossil-bearing strata are continuous in the Hefeng-Tongshan area (Fig. 1b, Supplementary Fig. 1c–e). As the materials were first discovered at the Jiweijian section, Tongshan County, Hubei Province, South China, we here name this fossiliferous deposit the Tongshan Lagerstätte.

Shaanxilithes (Supplementary Fig. 1f), a potential index fossil defining the base of the Ediacaran Stage 675–78, has a wide geographical occurrence in Hubei, Guizhou, Ningxia, Qinghai, Shaanxi, and Yunnan provinces of China79,80, northwestern India77, central and southeastern Siberia81–83, and possibly southern Namibia84 (Supplementary Fig. 2). The consistent appearance of Shaanxilithes in Tongshan County strengthens its potential of an index fossil by its massive occurrence over a short stratigraphic interval about 4 m in thickness (Fig. 1d, Supplementary Figs. 1d, e, 2). The Tongshan Lagerstätte is located at about 18 m below the 4 m thick siliceous shales containing the genus Shaanxilithes (Supplementary Fig. 1c–e). In the nearby Yangtze Gorges area of western Hubei Province, Shaanxilithes occurs in the uppermost 3.1 m interval of the Shibantan Member80, of which the lower half hosts the Shibantan Lagerstätte (Supplementary Fig. 1b)73,80. The upper carbonaceous mudstones/shales of the Denying Formation in the Hefeng-Tongshan area of southern Hubei are thus correlated to the Shibantan Member in the Yangtze Gorges area of western Hubei, and to the lowermost part of the Gaojiashan Member in the Ningqing area, Shaanxi Province (Supplementary Fig. 1), assuming a synchronous Shaanxilithes zone. Hence, the Tongshan Lagerstätte is most likely time equivalent to the Shibantan Lagerstätte (Fig. 1c, Supplementary Fig. 1). As the Shaanxilithes zone is stratigraphically directly above the Jiangchuan, Shibantan, and Tongshan Lagerstätten, our high-precision U-Pb tuff age of 543.74±0.87 Ma (Supplementary Fig. 2) from the Jiweijian section of Tongshan County may serve as a minimum age constraint for the three Lagerstätten. Since the Gaojiashan Lagerstätte in Shaanxi Province of China occurs above the Shaanxilithes biozone, the Tongshan and Shibantan Lagerstätten are likely older than the Gaojiashan Lagerstätte (Fig. 1c, Supplementary Fig. 1). The relatively few fossil Lagerstätten in the Neoproterozoic results in poor stratigraphic correlations and difficulty in understanding the true fossil ranges. Temporal ranges on the order of 10 Ma or longer for the Ediacaran biota or assemblages (Fig. 1c)85, compared to just about 2–3 Ma for the Cambrian ones86, limit our ability in understanding the evolutionary patterns and processes prior to the Cambrian explosion. Further high-precision geochronology from a variety of the Ediacaran Lagerstätten is required to address the problems regarding the evolution of multicellular life in the Neoproterozoic.

Social network analysis
Comparing related and adjacent biotas provides important information for understanding how palaeocommunities changed in space and time. Macro-organisms documented in the Lantian, Miaohe, Wenghui, Shibantan, Jiangchuan, Wulingshan, and Tongshan Lagerstätten are compiled in Supplementary Data 2. Social network analysis was performed in RStudio version 1.3.959.

Elemental mapping
Two frond specimens were selected for scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis using ZEISS GeminiSEM 360 attached with ULTIM MAX detector. For each specimen, two sites on the frond body and one site on the matrix were selected (Supplementary Fig. 7a, l). All sites were defined with a uniform area of approximately 1.12 mm × 0.84 mm, the data of which are presented in Table 1. An additional site, the fourth site, outlined with a red box in each specimen (Supplementary Fig. 7a, l), displays the difference in elemental distribution between the frond body and the matrix.

Zircon U-Pb geochronology
The tuff sample (JWJ23-D-01) from the Jiweijian (JWJ) Section, about 4.8 m above the Shaanxilithes zone, was analyzed by the U-Pb CA-ID-TIMS method, following the detailed procedures described by Ramezani et al. 87. Zircon separates were extracted from the ash sample using standard crushing, magnetic susceptibility, and high-density liquid techniques. Most zircons are prismatic with delicate glass (melt) inclusions parallel to their long axis under binocular microscope, suggesting a volcanic origin87.

The selected zircon grains were pretreated by a chemical abrasion procedure modified after Mattinson88, which involved thermal annealing in a 900 °C furnace for 60 h, followed by partial dissolution (leaching) in 29 M HF inside high-pressure Parr® vessels at 210 °C for 12 h in order to mitigate Pb-loss effects, which often lead to anomalously young dates. The partially dissolved grains underwent fluxing alternately with dilute HNO3 and 6 M HCl on a hot plate and in an ultrasonic bath, each for 1 h. After each ultrasonic step, the grains were rinsed with ultra-pure water to remove the leachates. Subsequently, the thoroughly rinsed zircon grains were spiked with the EARTHTIME ET535 mixed 205Pb-233U-235U tracer89,90 before complete dissolution in 29 M HF at 210 °C for 48 h. The zircon solutions were then dried down on a hot plate and redissolved in 6 M HCl inside high-pressure vessels at 180 °C overnight. The dissolved U and Pb were chemically purified by an HCl-based column chemistry method using AG1X-8 anion-exchange resin. The eluted U and Pb were dried down with 0.05 M H3PO4 and loaded with a silica gel emitter solution onto a zone-refined outgassed Re filament for mass spectrometry.

The U and Pb isotopic ratios were measured on an Isotopx® X62 multi-collector thermal ionization mass spectrometer equipped with a Daly photomultiplier ion-counting system at the Massachusetts Institute of Technology Isotope Laboratory. Pb isotopic ratios were measured as monoatomic Pb ions in a peak-hopping mode on the ion-counter, whereas U isotopes were measured as UO2+ in a static mode on three Faraday detectors simultaneously. Measured isotopic ratios were corrected for mass-dependent isotope fractionation in the mass spectrometer, as well as for U and Pb contributions from the spike and laboratory blanks. Common Pb in the analyses averaged 0.29 pg, all of which was attributed to laboratory blank, and its isotopic composition was determined from long-term measurements of the total procedural Pb blank in the lab (see Supplementary data 1 footnotes). The radiogenic 206Pb concentrations were also corrected for initial 230Th disequilibrium in zircon using a magma Th/U model ratio of 2.8±1.0 (2σ).

Data reduction, calculation of dates and propagation of uncertainties were carried out using the Tripoli version 3.7.1 and ET_Redux version 0.5.291,92. Uncertainties in the calculated weighted mean 206Pb/238U date are reported at 2σ level (Supplementary Fig. 3) and in the ±X/Y/Z Ma format, where X is the internal (analytical) uncertainty in the absence of all external errors, Y incorporates X and the U–Pb tracer calibration errors, and Z includes the latter as well as the decay constant errors of 93. The external uncertainties must be taken into account only if the results are compared with U–Pb dates obtained in other laboratories with different tracers, different techniques (e.g., microbeam U–Pb), or ones derived from other isotopic chronometers (e.g., 40Ar/39Ar).

All five analyzed zircons from the tuff sample JWJ23-D-01 overlap within their 2σ analytical uncertainties, yielding a weighted mean 206Pb/238U date of 543.74±0.87/0.98/1.1 Ma with a MSWD of 1.0. This date provides the best age estimate for the eruption of the tuff and a good approximation for the associated sedimentary depositional age.

Ages of Ediacaran Lagerstätten
The Ediacaran-Cambrian (E-C) boundary provides the lower age limit for comparison of the Ediacaran Lagerstätten. High-resolution CA-ID-TIMS geochronology from Namibia brackets the E-C transition between 539.18+0.17/−0.26 Ma and 538.30+0.14/−0.14 Ma94 or between 538.99±0.21 Ma and 538.58±0.19 Ma95, although the index fossil Treptichnus pedum was not recorded in any of the calibrated biostratigraphies. Defining the E-C boundary is outside the focus of this study; we here consider 538.8 Ma for the E-C boundary following the geologic timescale 16,94.

Wulingshan Lagerstätte (545–538.8 Ma). Wulingshan Lagerstätte was erected in 1999 based on collections from the middle portion of the Liuchapo Formation at Ligonggang town, Taoyuan County, western Hunan, South China96. The Liuchapo Formation at Ligonggang town has a total thickness of 39.8 m and is subdivided into the lower 6.8 m in thickness composed of siliceous rocks and carbonaceous siliceous slates, the middle 23 m in thickness with carbonaceous shales, and the upper 10 m in thickness composed of argillaceous siltstones and thin layered siliceous rocks. Without index fossils such as Shaanxilithes in the Liuchapo Formation, it is hard to make a stratigraphic correlation between the Tongshan and Wulignshan Lagerstätten. While the fossils described by Chen et al. 96 are macroalgae97, the absence of metazoans makes it difficult to correlate with the Tongshan Lagerstätte. By considering both Lagerstätten that share a high similarity of macroalgal forms, we suggest that they are stratigraphically close to each other. An ash layer among the cherts of the lower Liuchapo Formation in west Hunan has yielded a U-Pb CA-ID-TIMS age of 545.76±0.66 Ma98, suggesting that the Wulingshan Lagersätte is likely younger than 545 Ma99. Accordingly, we here consider its age between ~545 Ma and 538.8 Ma (Fig. 1c).

Shibantan Lagerstätte (previously known as Xilingxia Lagerstätte or Shibantan Assemblage; 551–544 Ma). The name complexity of the Xilingxia Fauna is discussed by Xiao et al. 26 and we here follow Xiao et al. in using the Shibantan Lagerstätte. The minimum age of the Shibantan Lagerstätte 26 has been considered 543.4±3.5 Ma based on the U-Pb zircon age of a tuffaceous layer from the Baimatuo Member in the Yangtze George area above the Shaanxilithes zone 100. This age assignment is consistent within uncertainty with our minimum age of 543.74±0.87 Ma for the Tongshan Lagerstätte mentioned above (Fig. 1c).

Jiangchuan Lagerstätte (551–544 Ma). Jiangchuan Lagerstätte was discovered from the Jiucheng Member of the Dengying Formation in Jiangchuan and Jinning, eastern Yunnan, South China101,102. Shaanxilithes occurs in the Xiaowaitoushan Member of the Zhujiaqing Formation in eastern Yunnan, stratigraphically far above the Jiucheng Lagerstätte102, which correlates the Jiangchuan Lagerstätte possibly to the Tongshan and Shibantan Lagerstätten.

Miaohe Lagerstätte (>551 Ma). Miaobe Lagerstätte was formally erected in 1992 by Ding and his colleagues103. The Miaohe Member, from which the Miaobe Biota was discovered, is either correlated to the Doushantuo Member IV67,104 or directly below the Shibantan Member of the Dengying Formation105. The recent data from the Miaohe Member suggest that the Miaohe Member is most likely correlated to the Doushantuo Member IV because of a slipping block incorporating both the Miaohe Member of the Doushantuo Formation and the Hamajing Member of the Dengying Formation106 (Fig. 1c).

Wenghui Lagerstätte (586–557 Ma). The Wenghui Biota107–109 at the Xiajiaomeng section in the Guizhou Province of South China occurs below an ash layer with a U-Pb zircon age of 557±3 Ma110. We here follow Yang et al. 110 to assign an age range to the Wenghui Biota slightly shorter than that of the Miaohe Biota. This biota has a maximum age of 585.7±2.8 Ma110 (Fig. 1c).

Image collection and preparation
The specimens were photographed using Olympus DSX1000 with DSX10-SXLOB 10X lens, Nikon SMZ25 with SHR Plan Apo 0.5x lens, and Sony ILCE-7RM4A with 50 mm lens. Olympus DSX1000 was equipped with a polarized filter. Both low-angle lighting under normal optical conditions and polarized light were used to capture different structural details of the specimens. Alcohol spreading on specimens was also applied in some conditions to enhance the contact between fossil and rock matrix. The continental reconstructions generated using GPlates 2.3.0 were modified from the plate model (Version 1.1b with a file name of SM2-4485738-V2) in Merdith et al. 111. Figure 1b is based on a geological map sourced from the publicly accessible GeoCloud platform and was created using Adobe Illustrator 26.0.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This paper documents a new late Ediacaran-aged lagerstätte from China, that preserves a mixture of algae, macroscopic protists, and apparent animals as carbonaceous impressions. The style of preservation offers a unique view into the morphology of several taxa, and – because it occupies a deeper-water setting than many contemporaneous deposits – the lagerstätte as a whole provides an interesting window into latest Ediacaran ecosystems that isn’t preserved in many other places.\nThis is a nicely written paper that I think should be published. It currently suffers from a couple of weaknesses that muddy the waters somewhat…but I’m confident that the authors can fix these without too much extra work. I’ve outlined these major points below, and then subsequently some more minor comments that should be easy to remedy.\n1. The algal and protistan fossils presented in the paper are beautifully preserved, and will provide the basis for fascinating research for years to come. However, I am less convinced by many of the metazoan (and supposedly frondose) fossils…and I think the authors could usefully take a step back from over-interpreting these. For example: with respect to the fossils shown in Figure 4a-d, even after combing through the images in the supplementary material I cannot see any convincing rangeomorph elements, and thus I think the identifications are highly speculative. I am similarly unconfident about the evidence for holdfasts…and without more examples I think it’s very hard to say anything about mode of life, or even what these fossils represent. Similarly, the fossil shown in Figure 4e shows little resemblance to Swartpuntia; for a start Swartpuntia possesses a segmented (or at least, ‘ornamented’) stem, and the spacing of putative erniettomorph tubular modules would be highly unusual for this taxon. This is a lengthy way of saying: I think it would be much more sensible to refer to these as ‘putative frondose metazoans’ – the paper doesn’t rely on these to be Bradgatia and Swartpuntia to be publishable in Nature Communications, and referring these fossils to specific Ediacaran genera distracts from what is otherwise a very exciting find. In place of this discussion, I think instead the paper would be strengthened with more information given on the preservation (see below):\n2. ‘Burgess shale-type’ preservation has been defined a few different ways, but is perhaps most commonly used to refer to soft-tissues preserved as carbonaceous impressions, sometimes with associated pyrite, and often with clay minerals that may or may not be diagenetic in origin. It would be fascinating if the authors could show some data pertaining to the preservation and lithological context of these new fossils – for example, it would be great if some SEM images or EDS elemental map data could be given, and which would allow the authors to compare their style of preservation to BST and other instances of carbonaceous compression fossils. Lastly, I think some pictures of the outcrop would be valuable; this would allow the reader to eyeball the sedimentology, and would help support the paleoenvironmental interpretation that is being offered.\nMinor comments:\n“Unlike many Cambrian Lagerstätten, Burgess Shale-type (BST) preservation is rare and moldic Ediacara-type preservation provides insight into the early evolution of metazoans including typical fronds” (line 15); this sentence appears to be saying two different things – I think it needs re-wording.\n“The large surface area of the new algae might have locally increased oxygen concentration via photosynthesis to facilitate metazoans” (line 87); this reads a little strangely, and feels like an unsupported statement. I suggest adding a reference, or removing if there is no previous work to support this being important in Ediacaran ecosystems.\n“…whether a stem is present remains unclear but present, the stem must have been short” (line 144); likewise, this sentence reads a little strangely…do the authors mean to write, ‘if a stem was originally present, it must have been short’?", "reviewer_2": "At present, the submitted paper describes Burgess Shale type preservation as that ‘which preserves original information on organic integument and internal soft tissues, in addition to hard exoskeletons.’ The paper then states ‘Unlike Cambrian Lagerstätten with BST preservation, the Ediacara Biota 43 features Ediacara-type preservation that preserves the outline of structures, but the original compositional information is unavailable.’\nIt is correct that many Ediacaran biota fossils are preserved as moulds or casts. However, while rarer than mouldic preservation, organic preservation of Ediacaran fossils is known for example from the White Sea assemblage. E.g. see Bobrovskiy et al 2019 Nature Ecology and Evolution:\nhttps://www.nature.com/articles/s41559-019-0820-7\n‘Preservation of organic matter plays an important role in the taphonomy of all fossils from the White Sea localities. A close investigation of dozens of Ediacaran macrofossils, including Dickinsonia, Andiva, Kimberella, Aspidella, Sabelliditides and Beltanelliformis collected from unweathered layers in the White Sea revealed that they all are preserved organically, including those that occur within sandstone or clay (Fig. 6a–d)6,7,45. ‘\nSee also Cai et al 2012 Palaeo^3:\nhttps://www.sciencedirect.com/science/article/pii/S003101821200082X\n‘Burgess Shale-type (BST) fossils often are preserved as two-dimensional carbonaceous compressions, sometimes aided by two mineralization processes: pyritization and aluminosilicification, defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials. Here we report similar mineralization modes within the late Ediacaran Gaojiashan Lagerstätte of southern Shaanxi Province, South China.’\nTherefore the manuscript should be updated in the light of known Ediacaran organic preservation.\nUnfortunately, the majority of the figure photographs do not show sufficient detail of the specimens to confirm their taxonomic attributions.\nFor example the manuscript states ‘Ten fan- and bush-like specimens belong to Bradgatia 104 sp. (Fig. 4a–b and Extended Data Fig. 7a–f) are one of the youngest appearances of this genus12,28 105 . Segments of branches are clearly visible (Extended Data Fig. 106 7a–f) and show 3D in morphology (Extended Data Fig. 7e–f).’\nHowever, figure 4 a and b show circular specimens with some irregular lines. If we compare these with Ediacaran specimens with exceptional preservation, that show their taxonomically distinctive features it is very difficult to confirm whether they may be of the same taxon or not.\nSimilarly in extended data fig 7 there is a large amount of textural noise in the images and it is not possible to confirm the presence of, for example, rangeomorph type fractal branching.\nThe fossil shown in Fig 4 c to d is very interesting. However, from these images it is difficult to confirm more than they show an elongate bag-like organism with at least first order branches, ribs or annulations.\nFig 4e is compared to Swartpuntia. However, this taxon is notable for having a wide aspect ratio which the figured specimen does not appear to share. What is the basis for the suggested attribution to this taxon as opposed to another taxon entirely?\nThe discussed holdfast is not clearly visible in the figures.\nOverall, I would suggest that there are two options available to the authors. First, either to improve, if possible, the images used to support the taxonomic attributions and to further explain and evaluate the evidence for specific attributions. Second, to make more tentative taxonomic attributions in the present paper. Perhaps a combination of these options could be pursued.", "reviewer_3": "In the Abstract (line 28) the authors state that their fossils will provide 'A new repository of original compositional information'. Likewise in the Introduction (line 49) ‘This study ... makes compositional information widely available to the Ediacaran metazoans such as fronds’ and Discussion (final line 238) 'the preservation ... will reveal more information on the original composition of Ediacaran metazoans'. However, this claim, which the authors appear to consider central to the significance of their paper, is nowhere supported by any chemical data. Note also that the composition will not be 'original' but diagenetically altered to longer chain compounds by polymerization.\n'Bat-shaped', 'tie-shaped' (lines 83,84), and 'corn-like' (line 136) are not useful descriptors as they will suggest different comparisons to different people. Likewise 'meandering-like' (line 94) is not going to prompt images of this specimen.\nThe surface area (line 88) would only be a significant source of oxygen if the algae occurred in dense groups. Is there any evidence of this?\nDoes 'undefined' (line 94) simply mean that the specimen in 3b is poorly preserved. Likewise (line 99) how confident are you that this specimen is an open tube or that the irregular opening represents the true termination.\nThe designation 'sp.' means that the material preserves features diagnostic of the genus yet cannot be assigned to a known species. If you use 'sp.' you need to justify its assignment to the genus, but also explain how it differs from other species of the genus in question. You achieve this to some extent in the case of Swartpuntia (line 126 ...) but not for Bradgatia (line 103 ...).\nFresh algae and animals can endure significant transport without damage. The preservation of holdfasts does not necessarily demonstrate that the organisms are buried in situ. Is there sedimentological evidence to support 'quick burial and in situ preservation' (line 179)?\nYou need citation(s) to the conventional view that there is no bias (line 202).\nIf you cite 53 on line 237 (Love et al. 2009) you should also cite the alternative more recent view: Bobrovskiy, I., Hope, J.M., Nettersheim, B.J., Volkman, J.K., Hallmann, C. and Brocks, J.J., 2021. Algal origin of sponge sterane biomarkers negates the oldest evidence for animals in the rock record. Nature Ecology & Evolution, 5(2), pp.165-168."}, "author_response": "We sincerely thank the reviewers for their thoughtful and constructive comments, which have been instrumental in strengthening the scientific rigor of our manuscript. In response to their valuable feedback, we have conducted a thorough revision of the text, significantly expanded our dataset, and refined our interpretations. We have toned down the results and discussions about the BST frond animals.\n\nKey improvements include:\n1) restricting frond materials to rangeomorphs;\n2) adding additional analytical data, including a new table (Table 1) and two supplementary figures (Figs. S7, S8), providing critical geochemical and sedimentological evidence that elucidates the preservation of this Lagerstätte;\n3) enhancing visual documentation, with all frond specimens—including a newly added specimen (Fig. 4)—rephotographed and presented as individual figures (Figs. 4–6). Low-angle lighting techniques were employed to better resolve fine morphological details, such as first- and second-order branches;\n4) providing the new Supplementary Figure S10, which shows the expansion of BST (Burgess Shale-type) preservation in Ediacaran fronds and the Ediacara Biota, reinforcing the broader implications of our findings.\nAll modifications are clearly highlighted in the revised manuscript (yellow background), and point-by-point responses to each comment are provided below.\n\nE ditorial feedback\n* Please replace any bar graphs with plots that feature information about the distribution of the underlying data. All data points should be shown for plots with a sample size less than 10. For larger sample sizes, please consider box-and-whisker or violin plots as alternatives. Measures of centrality, dispersion and/or error bars should be plotted and described in the figure legend.\n\nResponse:\nThank you for recognizing this detail. The vertical red bars in the Supplementary Figure S3 represent the rank order plot, which is the standard format for reporting the isotope dates (Condon et al. 2024, Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information, GSA Bulletin, 136, 4233–4251). It should be noted that each bar represents one individual zircon, which is comparable to the “individual points are shown when possible” in the Editorial Policy Checklist.\nWe have corrected the caption to become “The conventional concordia plot for sample JWJ23-D-01 shows individual zircon analyses with their 2σ error ellipses, and all individual analyses intersect the concordia line and are therefore concordant. The inset rank-order plot of the zircon 206Pb/238U dates shows individual zircon age results with 2σ uncertainty, and the horizontal black line with shaded bands signifies the calculated weighted mean 206Pb/238U age with 2σ error (X/Y/Z). z1 to z5 in the figure represent five zircon crystals analyzed using the CA-ID-TIMS method.”.\n\nREVIEWER COMMENTS\n\nReviewer #1 (Remarks to the Author):\n\nThis paper documents a new late Ediacaran-aged lagerstätte from China, that preserves a mixture of algae, macroscopic protists, and apparent animals as carbonaceous impressions. The style of preservation offers a unique view into the morphology of several taxa, and – because it occupies a deeper-water setting than many contemporaneous deposits – the lagerstätte as a whole provides an interesting window into latest Ediacaran ecosystems that isn’t preserved in many other places.\n\nThis is a nicely written paper that I think should be published. It currently suffers from a couple of weaknesses that muddy the waters somewhat…but I’m confident that the authors can fix these without too much extra work. I’ve outlined these major points below, and then subsequently some more minor comments that should be easy to remedy.\n\nResponse:\nWe sincerely appreciate your thoughtful assessment of our work and your recognition of the significance of this newly discovered late Ediacaran Lagerstätte. We have carefully addressed the major concerns raised in this point, which we acknowledge as critical to strengthening the manuscript. Below, we provide a detailed point-by-point response to your comments.\n\n1. The algal and protistan fossils presented in the paper are beautifully preserved, and will provide the basis for fascinating research for years to come. However, I am less convinced by many of the metazoan (and supposedly frondose) fossils…and I think the authors could usefully take a step back from over-interpreting these. For example: with respect to the fossils shown in Figure 4a-d, even after combing through the images in the supplementary material I cannot see any convincing rangeomorph elements, and thus I think the identifications are highly speculative. I am similarly unconfident about the evidence for holdfasts…and without more examples I think it’s very hard to say anything about mode of life, or even what these fossils represent. Similarly, the fossil shown in Figure 4e shows little resemblance to Swartpuntia; for a start Swartpuntia possesses a segmented (or at least, ‘ornamented’) stem, and the spacing of putative erniettomorph tubular modules would be highly unusual for this taxon. This is a lengthy way of saying: I think it would be much more sensible to refer to these as ‘putative frondose metazoans’ – the paper doesn’t rely on these to be Bradgatia and Swartpuntia to be publishable in Nature Communications, and referring these fossils to specific Ediacaran genera distracts from what is otherwise a very exciting find. In place of this discussion, I think instead the paper would be strengthened with more information given on the preservation (see below):\n\nResponse:\nWe have included a new specimen (now Fig. 4) that exhibits clearer fractal branching, reinforcing the presence of rangeomorph-type architecture in the Lagerstätte. This larger specimen help clarify the branching structures in Figs. 5–6. The fractal patterns in several forms of fossils are consistent with rangeomorphs. In accordance with your suggestion, we have removed definitive assignments to Bradgatia and Swartpuntia and now refer to these fossils as \"rangeomorphs\" or \"frondose metazoan\" throughout the text, emphasizing their uncertain affinity. Some taxonomic names of frondose animals mentioned in the main text are solely for comparative purposes.\n\n2. ‘Burgess shale-type’ preservation has been defined a few different ways, but is perhaps most commonly used to refer to soft-tissues preserved as carbonaceous impressions, sometimes with associated pyrite, and often with clay minerals that may or may not be diagenetic in origin. It would be fascinating if the authors could show some data pertaining to the preservation and lithological context of these new fossils – for example, it would be great if some SEM images or EDS elemental map data could be given, and which would allow the authors to compare their style of preservation to BST and other instances of carbonaceous compression fossils. Lastly, I think some pictures of the outcrop would be valuable; this would allow the reader to eyeball the sedimentology, and would help support the paleoenvironmental interpretation that is being offered.\n\nResponse:\nWe have added two supplementary figures (S7 and S8) and one table (Table 1) to support the discussion of preservation. Figure S7 displays the elemental maps of two frond specimens, and a summary of EDS spectra of both specimens is provided in Table 1. Figure S8 contains one field image and two thin sections.\nAs you have mentioned, we found high concentration of Fe in the body fossils, which is a good indicator of the exquisite preservation. The well-preserved laminated beds of mudstone/shales provide strong evidence of an environment that experienced a long duration of low-energy conditions, alternated with short duration of slightly high-energy conditions.\nIn the main text, we add “EDS analyses of two frond specimens display high concentrations of C, Fe, P, and possibly S in the body fossils, which contrast with the high concentrations of Mg, Al, K, Ti, and Ba in the matrix (Table 1, Supplementary Fig. 7). The high concentration of Fe in the body fossil indicates the exceptional preservation of soft-bodied fossils because pyrite, formed by iron reacting with sulfates, can quickly replace the soft tissues at the early stage of decay 4, 21, 40, 41, allowing the preservation of soft tissues. The low proportion of pyrite in fonds makes the Tongshan Biota most comparable to the preservation condition of the middle Cambrian Burgess Shale Lagerstätte (Supplementary Discussion). In addition, the Tongshan Lagerstätte, preserved in siliceous shales/mudstones dominated by silicate minerals, likely benefits from the rapid precipitation of silica cements, which has been an important factor for the preservation of mouldic Ediacara Lagerstätte 20.” in lines 179-191 and “Thin sections of shales/mudstones show parallel laminae composed of thick clay-rich background beds and thin silt-rich event beds (Supplementary Fig. 8). The thick clay-rich beds indicate a prolonged period of low-energy condition, alternating with short duration silt-rich beds formed under relatively higher energy. Periodic fluctuations in local environmental energy resulted in the rapid burial of organisms. In addition, these parallel beds lacking sedimentary features such as cross-stratification indicate that the deposition occurred below the storm wave base.” in lines 195-202.\nThe detailed discussion is also organized as one subsection in the Supplementary information: “Supplementary discussion – Geochemical and sedimentological evidence for the palaeoenvironment of the Tongshan Lagerstätte\nEDS analyses of soft-bodied fronds (Table 1, Supplementary Fig. 7A–W) display high concentrations of C, Fe, P, and possibly S, which are contrasting to the high concentrations of Mg, Al, K, Ti, and Ba in the matrix. Si and O have similar concentrations in both body fossils and the matrix. Aluminosilicates could partially fill the voids left by soft tissues in BST fossils 50-54. This explains why the body fossils have lower contents of aluminosilicate minerals than the matrix and indicates that the high concentrations of C, Fe, P, and possibly S, are true signals of body fossils. The presence of Fe in the body fossil is a direct indicator for exceptional preservation of soft-bodied fossils because irons react with sulfates to form pyrites, which can quickly replace the soft tissues at the early stage of decay 53, 55-57, allowing the preservation of soft tissues. During subsequent weathering, original pyrites could form iron oxides and, at the same time, the sulfuric acids released due to this alteration were washed away. This explains the lower content of S detected in the body fossils and the reddish color of the fossils. The presence of S further indicates the microenvironments around body fossils during burial were partially anoxic, allowing iron in the water columns to react with the sulfates surrounding the decay materials. The concentration of pyrites varies among Lagersätten. In the two most well-known BST Lagersätten, specimens of the middle Cambrian Burgess Shale Biota contain a lower proportion of pyrite compared to those of the lower Cambrian Chengjiang Biota 58. The low proportion of pyrite in fonds makes the Tongshan Biota most comparable to the preservation condition of Burgess Shale Biota.\nIn addition, the Tongshan Lagerstätte is preserved in siliceous shales/mudstones dominated by silicate minerals, which distinguishes it from most BST biotas preserved by early carbonate cements 59. This condition is likely related to the widespread weathering of continental crust near the terminal Ediacaran 60-62. While the rapid precipitation of silica cements has been an important factor for the preservation of mouldic Ediacara Biota 63, the Tongshan materials from the siliceous deposits likely benefit from this mechanism. The BST Tongshan Lagerstätte shares preservational mechanisms not only with the typical Burgess Shale Lagerstätte but also with the Ediacara Lagerstätte, representing an intermediate style that bridges the Ediacara-type and BST preservation and contributes to a better understanding the early evolution of life.\nThe dark-coloured, thick clay-rich layers represent slow sedimentation of clay particles from the water column, corresponding to the “background” beds, while the light-coloured, thin silt-rich layers represent the “event” beds (Supplementary Fig. 8A–C). Cyclic changes between clay-rich and silt-rich beds reflect periodic fluctuations in local environmental energy, resulting in the rapid burial of organisms. These parallel beds without cross-stratification indicate that the deposition occurred below the storm wave base. Many well-preserved BST Lagerstätten such as Qingjiang 64 show similar depositional phenomena.”\n\nMinor comments:\n\n“Unlike many Cambrian Lagerstätten, Burgess Shale-type (BST) preservation is rare and moldic Ediacara-type preservation provides insight into the early evolution of metazoans including typical fronds” (line 15); this sentence appears to be saying two different things – I think it needs re-wording.\n\nResponse:\nWe revised it to become “Because the informative Burgess Shale-type preservation is rare in the Ediacaran, mouldic Ediacara-type preservation provides insight into the early evolution of metazoans including typical fronds”. This highlights the rarity of BST preservation in the Ediacaran, and our work provides such preservation for early animals.\n\n“The large surface area of the new algae might have locally increased oxygen concentration via photosynthesis to facilitate metazoans” (line 87); this reads a little strangely, and feels like an unsupported statement. I suggest adding a reference, or removing if there is no previous work to support this being important in Ediacaran ecosystems.\n\nResponse:\nThis sentence had been deleted from the main text.\n\n“…whether a stem is present remains unclear but present, the stem must have been short” (line 144); likewise, this sentence reads a little strangely…do the authors mean to write, ‘if a stem was originally present, it must have been short’?\n\nResponse:\nRight. We have corrected this sentence to become “…whether a stem is present remains unclear. However, if a stem was originally present, it must have been short.”\n\nReviewer #2 (Remarks to the Author):\n\nAt present, the submitted paper describes Burgess Shale type preservation as that ‘which preserves original information on organic integument and internal soft tissues, in addition to hard exoskeletons.’ The paper then states ‘Unlike Cambrian Lagerstätten with BST preservation, the Ediacara Biota 43 features Ediacara-type preservation that preserves the outline of structures, but the original compositional information is unavailable.’\n\nIt is correct that many Ediacaran biota fossils are preserved as moulds or casts. However, while rarer than mouldic preservation, organic preservation of Ediacaran fossils is known for example from the White Sea assemblage. E.g. see Bobrovskiy et al 2019 Nature Ecology and Evolution:\nhttps://www.nature.com/articles/s41559-019-0820-7\n‘Preservation of organic matter plays an important role in the taphonomy of all fossils from the White Sea localities. A close investigation of dozens of Ediacaran macrofossils, including Dickinsonia, Andiva, Kimberella, Aspidella, Sabelliditides and Beltanelliformis collected from unweathered layers in the White Sea revealed that they all are preserved organically, including those that occur within sandstone or clay (Fig. 6a–d)6,7,45. ‘\n\nResponse:\nWe appreciate that you mentioned one of the breakthroughs among the Ediacara-type fossils in recent years. We fully acknowledge the groundbreaking work of Bobrovskiy et al. (2019) demonstrating organic preservation in White Sea Ediacaran fossils and many other related works that have been already cited in line 259 of our paper. However, we wish to clarify several key distinctions. The White Sea examples represent a specialized case of organic preservation within Ediacara-type taphonomy (primarily in coarse-grained sandstones). Our Tongshan material exhibits true BST preservation (carbonaceous compression in fine-grained mudstones/shales). The Tongshan Lagerstätte provides the first clear evidence of BST preservation for Ediacaran frondose organisms. This represents a distinct taphonomic pathway from both classic Ediacara-style preservation and the Ediacara-style preservation with the organic preservation. The BST Tongshan Lagersätte bridges the gaps between traditional Ediacara-type preservation, Ediacara-type preservation with organic remains (as seen in Bobrovskiy et al. 2019), and BST preservation. It also helps bridge the taphonomic continuum between Ediacaran and Cambrian preservation styles. Our findings complement rather than contradict previous work. We have modified the relevant text in the last paragraph of the Discussion, added the Supplementary Figure 10 to more precisely articulate these distinctions, and included references to Bobrovskiy et al.'s important work.\n\nSee also Cai et al 2012 Palaeo^3:\nhttps://www.sciencedirect.com/science/article/pii/S003101821200082X\n‘Burgess Shale-type (BST) fossils often are preserved as two-dimensional carbonaceous compressions, sometimes aided by two mineralization processes: pyritization and aluminosilicification, defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials. Here we report similar mineralization modes within the late Ediacaran Gaojiashan Lagerstätte of southern Shaanxi Province, South China.’\n\nTherefore the manuscript should be updated in the light of known Ediacaran organic preservation.\n\nResponse:\nWe completely agree with the reviewer that BST preservation does occur in the Ediacaran, as demonstrated by Cai et al. and others. Our study complements these previous findings by documenting the first known case of BST preservation specifically for frondose Ediacaran organisms. We have considered the discussion of the Gaojiashan biota (Cai et al. 2012) into our treatment of Ediacaran BST preservation.\nThe work of MacGabhann (MacGabhann, 2014, Geoscience Frontiers, 5, 53-62) provided a comprehensive summary about the preservation of Ediacara Biota (fig. 2 in MacGabhann, 2014). Although other modes of preservation exist among Ediacaran organisms, the “moulds+casts (fig. 2 in MacGabhann, 2014) is the dominated one in the Ediacara Biota. The frondose metazoans such as rangeomorphs are uniquely preserved as the moulds and casts. Our work extends the preservation of these typical Ediacaran metazoans with BST mode. Following your suggestion, we also have added a new Supplementary Figure S10 to better illustrate: Panel A: The traditional paradigm of Ediacara Biota and frondose animals; Panel B: How our findings expand this understanding.\nThe important carbonaceous and/or organic preservation related to fronds, the main focus of this work, is discussed in the main text. Following your suggestions, we have added new content to the final paragraph of the main text to clarity this issue: “Laboratory simulations have indicated that fossils of the Ediacara Biota preserve not only the external morphology but also the morphology of soft external or internal organic “skeletons” 58. Also, presence of organic matters has played an important role in the preservation of fine details of early metazoans through the Ediacara-type preservation 58. Analytical techniques such as biomarkers and stable isotopic data have helped to solve long-standing debates by revealing original compositional information of tissues 59-63. The BST preservation of the Ediacara Biota reinforces these observations and offers greater opportunities to examine internal “skeletons” or structures in detail, devoting to solve long-standing debates related to the early evolution of metazoans.”\nHowever, for other BST preservation of other Ediacaran organisms, we had concluded in a subsection “Supplementary discussion – BST preservation in the Ediacaran period ” in the supplementary information. Cai et al.’s work (2012) is also cited in the line 298 in this section.\n\nUnfortunately, the majority of the figure photographs do not show sufficient detail of the specimens to confirm their taxonomic attributions.\n\nResponse:\nWe recognized that using a polarized filter for photograph is a problem in showing the details of fronds in the previous version. All frond specimens have been completely rephotographed using low-angle lighting to enhance topological features. We have included a new specimen in Figure 4 that particularly well demonstrates the characteristic features, and we have carefully re-examined all specimens in Figures 5-6 to ensure their diagnostic features are now clearly visible. For particularly delicate structures, we have included detailed close-up insets where appropriate and provided multiple viewing angles for key specimens. The improved photographs better reveal the fractal branching patterns characteristic of rangeomorphs and fine structural details of putative holdfast regions.\n\nFor example the manuscript states ‘Ten fan- and bush-like specimens belong to Bradgatia 104 sp. (Fig. 4a–b and Extended Data Fig. 7a–f) are one of the youngest appearances of this genus12,28 105 . Segments of branches are clearly visible (Extended Data Fig. 106 7a–f) and show 3D in morphology (Extended Data Fig. 7e–f).’\nHowever, figure 4 a and b show circular specimens with some irregular lines. If we compare these with Ediacaran specimens with exceptional preservation, that show their taxonomically distinctive features it is very difficult to confirm whether they may be of the same taxon or not.\n\nResponse:\nWe have removed all specific genus-level assignments (e.g., Bradgatia) from the manuscript. The specimens are now conservatively comparable to the rangeomorphs. The description now focuses on general rangeomorph characteristics rather than specific taxonomic features. In addition, comparative discussions have been refined to highlight similarities in overall morphology rather than specific taxonomic identities. We have enhanced the figures using with multiple angle-lighting to better reveal the observable morphological features. We fully agree with the reviewer that making the definitive taxonomic assignments is challenging, and we sincerely appreciate this opportunity to strengthen our manuscript's scientific rigor. These revisions maintain the important paleontological significance of these specimens while adopting a more appropriately conservative approach to their interpretation.\n\nSimilarly in extended data fig 7 there is a large amount of textural noise in the images and it is not possible to confirm the presence of, for example, rangeomorph type fractal branching.\n\nResponse:\nWe have rephotographed all frond specimens without using a polarized filter, and the structural details are more clearly displayed under low-angle lighting. As the contents have been reorganized, the details displayed in previous extended data figure 7 have been moved to the main figures. Please check the new figures (Figs. 4-6) for the fractal branching, which has been shown in the close-up images.\n\nThe fossil shown in Fig 4 c to d is very interesting. However, from these images it is difficult to confirm more than they show an elongate bag-like organism with at least first order branches, ribs or annulations.\n\nResponse:\nThis specimen (Fig. 6A-B) was rephotographed under low-angle lighting. Some secondary-order branches are clearly visible (Fig. 6C). We limit our description and discussion of this specimen to its interpretation as a rangeomorph.\n\nFig 4e is compared to Swartpuntia. However, this taxon is notable for having a wide aspect ratio which the figured specimen does not appear to share. What is the basis for the suggested attribution to this taxon as opposed to another taxon entirely? The discussed holdfast is not clearly visible in the figures.\n\nResponse:\nThis specimen (Fig. 6E) raises a concern due to its significantly weathered condition compared to other materials. We provide a general description of it and state that it is a frond animal in line 157.\n\nOverall, I would suggest that there are two options available to the authors. First, either to improve, if possible, the images used to support the taxonomic attributions and to further explain and evaluate the evidence for specific attributions. Second, to make more tentative taxonomic attributions in the present paper. Perhaps a combination of these options could be pursued.\n\nResponse:\nWe have carefully implemented both recommended approaches to strengthen our manuscript. All frond specimens have been rephotographed using optimized techniques: removed polarizing filters that previously reduced clarity; applied low-angle lighting to enhance topological features; and captured multiple views of key specimens. The new images (including the additional specimen in Fig. 4) now more clearly show first- and second-order branching patterns. We have also adopted more tentative taxonomic attributions throughout: removed all species-level identifications, focused on broader rangeomorph affinity rather than precise classification. The results and discussion now emphasize observed morphological features rather than taxonomic assignments, comparisons with known rangeomorph characteristics, and the significance of BST preservation for these Ediacaran forms. We have also provided an additional specimen (Fig. 4) as particularly clear examples of diagnostic rangeomorph branching patterns, three-dimensional preservation of frond elements, and consistent morphology across multiple specimens. We believe these revisions have significantly strengthened the manuscript by providing better visual documentation of key features, adopting more appropriate taxonomic caution and maintaining the important scientific implications of these finds.\n\nReviewer #3 (Remarks to the Author):\n\nIn the Abstract (line 28) the authors state that their fossils will provide 'A new repository of original compositional information'. Likewise in the Introduction (line 49) ‘This study ... makes compositional information widely available to the Ediacaran metazoans such as fronds’ and Discussion (final line 238) 'the preservation ... will reveal more information on the original composition of Ediacaran metazoans'. However, this claim, which the authors appear to consider central to the significance of their paper, is nowhere supported by any chemical data. Note also that the composition will not be 'original' but diagenetically altered to longer chain compounds by polymerization.\n\nResponse:\nWe appreciate your insightful comment regarding our use of the term “original compositional information.” We acknowledge that diagenetic alteration (e.g., polymerization of organic compounds) modifies the primary chemistry of fossils. However, Burgess Shale-type (BST) preservation uniquely retains both morphological and geochemical evidence that reflects original biological structures, even if the organic molecules themselves have undergone diagenetic transformation.\nFor illustrating this issue and background information better, we revised the description and expanded the explanation of original compositional information for BST preservation in the introduction as “…, which preserves compositional information in both chemical and morphological aspects of organic integuments such as cuticle details 6, 7 and internal soft tissues such as muscles, gut systems, and nervous systems 8-11, in addition to hard exoskeletons” in the introduction. The word “Original” is removed from this sentence. In the revision, we emphasize that the BST preservation retains the compositional information in both chemical and morphological aspects. Chemical information represents only one part of the original information and includes the modified compounds you mentioned. The morphological information includes both external and internal structural details, such as the morphology of gut and gut glands, nervous systems, brains, different layers of cuticle, and internal details of spines.\nWe here use the spine as an example to explain the difference between the Ediacara-type and BST preservation. In Ediacara-type preservation, the spine is left only with an empty envelope-like morphology, such as external or internal moulds (e.g., Coronacollina acula in Clites et al. 2012, Geology, 40, 307-310). In contrast, in BST preservation, the spine or claw can show multiple internal structural layers (e.g., Hallucigenia sparsa in Smith and Ortega-Hernandez, 2014, Nature, 514, 363-366), which can further be distinguished based on their chemical compositions, appearing as dark- and light-colored regions. This represents a key advantage of BST preservation. Discovering more Ediacaran metazoans with BST preservation would provide access to additional structural details, offering great insights into the early evolution of metazoans.\nTo present the chemical composition, we have added Table 1 and Supplementary Figures S7 and S8 to display the preservational information, which is organized as a subsection in the Supplementary information: “Supplementary discussion - Supplementary discussion – Geochemical and sedimentological evidence for the palaeoenvironment of the Tongshan Lagerstätte”. Main text also includes this information in lines 179-202.\nIn the revised Abstract, we have modified the last sentence to become “The rarity of Burgess Shale-type preservation of fronds reflects the rarity of fine-grained deposits in the Ediacaran Period and expands the Ediacara biota with an informative repository oftissue and integument composition”.\nIn summary, while we agree that \"original composition\" must be interpreted through the lens of diagenesis, BST fossils nonetheless provide the closest available record of Ediacaran tissue systems. Our revisions clarified terminology, incorporate new geochemical data, and reframe the significance of BST preservation for early metazoan evolution.\n\n'Bat-shaped', 'tie-shaped' (lines 83,84), and 'corn-like' (line 136) are not useful descriptors as they will suggest different comparisons to different people. Likewise 'meandering-like' (line 94) is not going to prompt images of this specimen.\n\nResponse:\nFor better illustrating these shapes, we have reworded these descriptions with more details.\n1) A tie-shaped form (3F) is corrected as “an irregular circular form”.\n2) “A bat-shaped form” (3E) is corrected to become “a baseball bat-like form with an expanded distal end”.\n3) “A corn-like outline” (5G) is modified as “….a spherocylindrical outline….”.\n4) We have deleted the word “meandering-like” and replaced the description of the specimen (Fig 3B) with “A tubular structure showing segment-like divisions, …”.\n\nThe surface area (line 88) would only be a significant source of oxygen if the algae occurred in dense groups. Is there any evidence of this?\n\nResponse:\nWe have deleted this sentence from the main text after carefully reviewing the weakness of its argument.\n\nDoes 'undefined' (line 94) simply mean that the specimen in 3b is poorly preserved. Likewise (line 99) how confident are you that this specimen is an open tube or that the irregular opening represents the true termination.\n\nResponse:\nRegarding the specimen in Fig. 3B, the term \"undefined\" refers to certain morphological features being less distinct due to taphonomic factors, not necessarily poor overall preservation. The specimen retains diagnostically important characteristics despite partial obscuration. The key features supporting our identification include segment-like divisions (marked with brackets), elliptical segment outlines characteristic of cloudiniids, and cone-in-cone construction at the distal end (matrix-filled areas). These features are visible in new photograph taken without polarization to minimize optical artifacts and allow us to make the argument that it is comparable to cloudiniids.\nWe agree the apparent opening at top may not represent the true termination. We have modified the description to: \"A tubular structure showing segment-like divisions and its distal portion showing irregular opening at top may be related to cnidarians or annelids…”..\n\nThe designation 'sp.' means that the material preserves features diagnostic of the genus yet cannot be assigned to a known species. If you use 'sp.' you need to justify its assignment to the genus, but also explain how it differs from other species of the genus in question. You achieve this to some extent in the case of Swartpuntia (line 126 ...) but not for Bradgatia (line 103 ...).\n\nResponse:\nWe have toned down our results and discussions. Descriptions of frond materials are restricted to general features that are characteristic of the Rangeomorpha. All discussions of lifestyles and occurrences for Bradgatia and Swartpunita have been removed. Thus, we maintain our focus on the BST fronds rather than assigning them to a particular genus or species. The revised manuscript presents these specimens as important examples of BST-preserved rangeomorphs without assigning them to a particular genus or species.\n\nFresh algae and animals can endure significant transport without damage. The preservation of holdfasts does not necessarily demonstrate that the organisms are buried in situ. Is there sedimentological evidence to support 'quick burial and in situ preservation' (line 179)?\n\nResponse:\nWe integrate multiple lines of evidence to substantiate the “quick burial and in situ preservation”.\n1) Beltanelliformis colonies (Fig. 2H) exhibit closely spaced but non-overlapping individuals, consistent with undisturbed growth rather than postmortem accumulation. This spatial arrangement is a hallmark of in situ preservation in Ediacaran settings. Another example is that the holdfast of one new frond (Fig. 6D) is preserved parallel to bedding, with morphological features (e.g., a disc standing out from the central stalk or stem) suggesting it is originally anchored to the seafloor, rather than transported.\n2) A high concentration of pyrite in the frond body (Table 1; Supplementary Figure 7) indicates localized microbial sulfate reduction in a confined microenvironment—a process requiring rapid organic matter burial to prevent oxidative degradation.\n3) Laminated clay-silt alternations in thin sections (Supplemetnary Figure 8) reveal that background sedimentation (clay-rich laminae) reflects prolonged low-energy conditions, allowing undisturbed microbial mat development and organism colonization; event beds (silt-rich laminae) represent episodic, slightly higher-energy pulses that rapidly entombed benthic communities without erosive disruption; absence of cross-stratification or scour features suggests minimal reworking, supporting the interpretation of sudden burial.\nIn conclusion, the combined biological, geochemical, and sedimentological data align with Burgess Shale-type (BST) taphonomic models, where event-driven rapid burial facilitated exceptional preservation of in situ communities.\nWe organized the geochemical and sedimentological evidence as one subsection (lines 207-249), “Supplementary discussion – Geochemical and sedimentological evidence for the palaeoenvironment of the Tongshan Lagerstätte”, in the Supplementary information.\nIn the main text, we added “EDS analyses of two frond specimens display high concentrations of C, Fe, P, and possibly S in the body fossils, which contrast with the high concentrations of Mg, Al, K, Ti, and Ba in the matrix (Table 1, Supplementary Fig. 7). The high concentration of Fe in the body fossil indicates the exceptional preservation of soft-bodied fossils because pyrite, formed by iron reacting with sulfates, can quickly replace the soft tissues at the early stage of decay 4, 21, 40, 41, allowing the preservation of soft tissues. The low proportion of pyrite in fonds makes the Tongshan Biota most comparable to the preservation condition of the middle Cambrian Burgess Shale Lagerstätte (Supplementary Discussion). In addition, the Tongshan Lagerstätte, preserved in siliceous shales/mudstones dominated by silicate minerals, likely benefits from the rapid precipitation of silica cements, which has been an important factor for the preservation of mouldic Ediacara Lagerstätte 20.” in lines 179-191 and “Thin sections of shales/mudstones show parallel laminae composed of thick clay-rich background beds and thin silt-rich event beds (Supplementary Fig. 8). The thick clay-rich beds indicate a prolonged period of low-energy condition, alternating with short duration silt-rich beds formed under relatively higher energy. Periodic fluctuations in local environmental energy resulted in the rapid burial of organisms. In addition, these parallel beds lacking sedimentary features such as cross-stratification indicate that the deposition occurred below the storm wave base.” in lines 195-202.\n\nYou need citation(s) to the conventional view that there is no bias (line 202).\n\nResponse:\nWe cite a landmark work (Buatois et al. 2014, Nature Communications, 5, 3544) here to represent the conventional view.\n\nIf you cite 53 on line 237 (Love et al. 2009) you should also cite the alternative more recent view: Bobrovskiy, I., Hope, J.M., Nettersheim, B.J., Volkman, J.K., Hallmann, C. and Brocks, J.J., 2021. Algal origin of sponge sterane biomarkers negates the oldest evidence for animals in the rock record. Nature Ecology & Evolution, 5(2), pp.165-168.\n\nResponse:\nBy following your suggestion, we cited Bobroskiy et al. (2021) in this sentence."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The paper is substantially improved - the authors have backed off the specific genus designations, and have presented some new specimens which are more convincingly rangeomorphs. I am also grateful that elemental maps are shown (in Supp. Fig. 7), which give vlauable context. If I was being nitpicky, the figure doesn't seem to present maps of fossils vs. matrix; some importatn information is thus hidden, and preventing a proper comparison. Ideally, one of the maps would encompass the border between the fossil and matrix, so enrichments in specific elements are clearer.\nOtherwise, I think this is close to being publishable. Two final comments are below:\n\"pyrite, formed by iron reacting with sulfates, can quickly replace the soft tissues at the early stage of decay, allowing the preservation of soft tissues\" (line 183); the authors may wish to cite Gibson et al. (2023) in Geobiology, who were able to experimentally replicate the formation of pyrite in association with decaying diploblasts and triploblasts.\n\"BST preservation of typical fronds indicates that Ediacara-type preservation, which largely occurs in coarse grained deposits such as sandstones, is restricted by available rocks\" (line 239); similar to the comment above; Gibson et al. (2023) showed that the iron content of sediments is likely also an important control on Ediacaran-style preservation, and which hints at secular and paleogeographic biases.", "reviewer_2": "As detailed in their point by point response to review the authors have provided additional information and revised the text of their manuscript describing a fascinating new fossil biota. However, I would still suggest they go further in re-framing their discoveries to be less dependent on specific affinities of some of the fossils to Ediacaran taxa, which remain uncertain. The authors have provided a new figure 4, which they link to Rangeomorpha. However, given the difficulty in assessing branching structure from photographs, I am unable to verify the presence of rangeomorph elements.\nI would suggest rephrasing the text throughout to suggest plausible affinities, and not to frame the paper in terms of novelty dependent on the more uncertain of these affinities, which I don’t believe is necessary for this to be a very interesting and publishable paper.\nFor example, I would suggest modifying line 17 of the abstract to briefly describe the whole diversity of fossils they have found and the range of their plausible affinities e.g. all the protists, algae, metazoans they have identified, and mentioning apparent fronds within this without focusing on them so heavily.\nInstead of 'representing the Rangeomorpha’ in the abstract, I would suggest briefly including some of the more nuanced discussion of the BST preservation which the authors included in their point by point response e.g. summarising their response:\n‘Our Tongshan material exhibits true BST preservation (carbonaceous 244 compression in fine-grained mudstones/shales).’\n‘The BST Tongshan 248 Lagersätte bridges the gaps between traditional Ediacara-type preservation, Ediacara249 type preservation with organic remains (as seen in Bobrovskiy et al. 2019), and BST 250 preservation.’\nI would suggest similar re-framing throughout.", "reviewer_3": "The authors have dealt with two major issues raised by the reviewers. The quality of the illustrations is greatly improved and a new specimen added. The evidence for fractals is difficult to demonstrate but is now much clearer. The taxonomic assignments are more generalized to reflect the nature of the material.\nThe authors have added EDS data (Figure S7 and Table 1). Table 1 provides weight per cent data but there is no information in Methods indicating whether these are based on the area mapped or spot samples. Unfortunately Figure S7 includes maps of one site on each specimen only whereas three were mapped. It would be useful to include the maps for the other areas (particularly the matrix). Needless to say maps convey different information to weight percent data, specifically element distribution, and overlap of different elements provides an indication of the minerals present.\nGiven that the EDS data are important to the interpretation of the preservation (BST-type or not) that information should be moved from Discussion to Results. Note that the high concentration of Fe in the body fossil does not, per se, indication exceptional preservation, and the evidence for pyrite is weak at best: Fe and S coincide somewhat in Figure S7 C and K, but not in N and V (indeed S is essentially absent in V). Likewise the fact that the lithology is dominated by silicates does not allow a silica (i.e. quartz) cement to be inferred: the silicates are presumably clays as petrography of the thin sections would confirm. A high concentration of P is mentioned (line 180) but there is no discussion of its significance and a map of P is omitted for the first frond specimen in Figure S7!\nGiven the thickness of the silt laminae (Figure S8) it is hard to imagine rapid burial of in situ fronds.\nThe message in Figure S10 is not clear (to this reviewer at least). BST preservation is already included in the Ediacaran in MacGabhann's original (2014) diagram, which is identical to A here, so what does this figure add.? And coloring most the Ediacaran in green in B obscures information rather than adding to it.\nFinally, even though the authors have removed mention of 'original' chemical composition Reviewer 3's concerns about the inclusion of phrases such as 'informative repository of tissue and integument composition' and 'compositional information in both chemical and morphological aspects' remain. This issue needs to be clarified so that it is obvious that what is meant is the composition of the fossils, not the composition of the original tissues. This confusion is exemplified in the authors' response where they state that 'In contrast, in BST preservation, the spine or claw can show multiple internal structural layers (e.g., Hallucigenia sparsa in Smith and Ortega-Hernandez, 2014, Nature, 514, 363-366), which can further be distinguished based on their chemical compositions, appearing as dark- and light-colored regions.' That paper includes no chemical data and it is very unlikely that the dark and light colored regions differ significantly in either their original (presumably chitin-protein) or diagenetically altered state."}, "author_response": "1 Manuscript ID: NCOMMS-25-02355-A\n\nWe thank the reviewers once again for their time and valuable feedback. The current revision, including an addition of supplementary data and a reorganization of text, has been made in response to these comments.\n\nMajor improvements:\n1) Additional EDS analysis has been conducted, and the corresponding data are now presented in the new Supplementary Figure S7, which clearly shows the separation between the fossil body and the matrix. (Reviewers 1 and 3)\n2) Abstract has been revised to incorporate more general information on preservation. (Reviewer 2)\n3) The caption of Supplementary Figure S10 has been added with new information to clarify the difference between figure S10A and S10B. (Reviewer 3)\n4) Description of EDS analysis has been moved to the Results section. (Reviewer 3)\n\nModified text is highlighted with a yellow background and point-to-point responses to comments are showing below.\n\nREVIEWER COMMENTS\n\nReviewer #1 (Remarks to the Author):\n\nThe paper is substantially improved - the authors have backed off the specific genus designations, and have presented some new specimens which are more convincingly rangeomorphs. I am also grateful that elemental maps are shown (in Supp. Fig. 7), which give vlauable context. If I was being nitpicky, the figure doesn't seem to present maps of fossils vs. matrix; some importatn information is thus hidden, and preventing a proper comparison. Ideally, one of the maps would encompass the border between the fossil and matrix, so enrichments in specific elements are clearer.\n\nResponse:\nThank you for highlighting this point, which helps to make the chemical data more clearly visible. We have conducted an additional analysis that includes both the fossil body and the matrix in each elemental map. Please refer to the new Supplementary Figure S7.\n\nOtherwise, I think this is close to being publishable. Two final comments are below:\n\n\"pyrite, formed by iron reacting with sulfates, can quickly replace the soft tissues at the early stage of decay, allowing the preservation of soft tissues\" (line 183); the authors may wish to cite Gibson et al. (2023) in Geobiology, who were able to experimentally replicate the formation of pyrite in association with decaying diploblasts and triploblasts.\n\nResponse:\nWe appreciate you bringing up this experimental work, which is closely related to our study. We have cited this work at the end of this sentence on line 191.\n\n\"BST preservation of typical fronds indicates that Ediacara-type preservation, which largely occurs in coarse grained deposits such as sandstones, is restricted by available rocks\" (line 239); similar to the comment above; Gibson et al. (2023) showed that the iron content of sediments is likely also an important control on Ediacaran-style preservation, and which hints at secular and paleogeographic biases.\n\nResponse:\nWe appreciate this evidence in helping to decipher the preservation condition of Ediacaran organisms. We have added following sentence to lines 254-257: “As the iron weight percentage of sediment (iron:sediment) plays an important role in Ediacara-type preservation and is generally higher in shales than in sandstones42, preservation bias for Ediacaran organisms is further highlighted by the rarity of available deposits, such as mudstones from the Ediacaran period.”\n\nReviewer #2 (Remarks to the Author):\n\nAs detailed in their point by point response to review the authors have provided additional information and revised the text of their manuscript describing a fascinating new fossil biota. However, I would still suggest they go further in re-framing their discoveries to be less dependent on specific affinities of some of the fossils to Ediacaran taxa, which remain uncertain. The authors have provided a new figure 4, which they link to Rangeomorpha. However, given the difficulty in assessing branching structure from photographs, I am unable to verify the presence of rangeomorph elements.\n\nResponse:\nWe understand your concerns, as these are the first BST frond materials presented to us. Notably, considering that the first organism of the Ediacara Biota was described in 1872, it has been over 150 years during which the Ediacaran fronds have only been observed with Ediacara-type (or mouldic) preservation.\nWe followed a systematic procedure to assign these materials to rangeomorphs, considering the first-round comments from you and the other two reviewers.\nFirstly, there are no other contemporary or Ediacaran organisms, except the typical fronds, that can be compared to these materials. We appreciate your agreement on this point. Secondly, the fronds can be divided into three major categories: rangeomorphs, arboreomorphs, and erniettomorphs. Erniettomorphs, which process only one-order branches, can be excluded, as the Tongshan materials display more than one order of branches. The overall morphology of Erniettomorphs is also different from most Tongshan materials, with the except of the specimen in Figure 6E. Arboreomorphs bear “pods” and units (figure 6 in Dunn et al.. 2019, Palaoentology, v. 62, part 5, p. 851-865), and our materials don’t show such traits. The presence of first-order branches and its associated perpendicular branches makes most Tongshan materials comparable to rangeomorphs. Finally, there is no evidence for us to treat the Tongshan materials different from these three major categories. In summary, assigning these BST materials to rangeomorphs is most appreciate classification based on the current understanding of Ediacaran organisms.\n\nI would suggest rephrasing the text throughout to suggest plausible affinities, and not to frame the paper in terms of novelty dependent on the more uncertain of these affinities, which I don’t believe is necessary for this to be a very interesting and publishable paper.\n\nResponse:\nWe really appreciate that you provide us the thoughtful comments, which are devoted to strengthen this work. If the Tongshan Biota contains only type of fronds, it would be difficult to make the argument we have presented. However, four types of fronds have been identified, all displaying similar patterns of branches, the first- and second-order branches (Figs. 4-6). Multiple lines of evidence including total morphology support the assignment to rangeomorphs. The branching styles or characters of these BST fronds don’t support an argument that that they are different from rangeomorphs. We do appreciate this comment, but we believe it is more appropriate to remain the assignment to rangeomorphs rather than attribute them to unknown or uncertain organisms.\n\nFor example, I would suggest modifying line 17 of the abstract to briefly describe the whole diversity of fossils they have found and the range of their plausible affinities e.g. all the protists, algae, metazoans they have identified, and mentioning apparent fronds within this without focusing on them so heavily.\n\nResponse:\nWe have revised the first sentence to become “…..provides insight into the early evolution of organisms like metazoans (including typical fronds), protists, and algae.” The Tongshan Lagerstatte is unique for its BST-preserved fronds, which represent one of the central arguments in our paper. The final sentence of the abstract, which has been revised based on your comment below, clearly reflects the broader significance of the Tongshan Lagerstatte and its BST preservation. Therefore, we here keep the ”typical fronds” in this sentence, as it highlights the key discovery in this new Lagerstatte.\n\nInstead of 'representing the Rangeomorpha’ in the abstract, I would suggest briefly including some of the more nuanced discussion of the BST preservation which the authors included in their point by point response e.g. summarising their response:\n\n‘Our Tongshan material exhibits true BST preservation (carbonaceous 244 compression in fine-grained mudstones/shales).’ ‘The BST Tongshan 248 Lagersätte bridges the gaps between traditional Ediacara-type preservation, Ediacara249 type preservation with organic remains (as seen in Bobrovskiy et al. 2019), and BST 250 preservation.’\n\nI would suggest similar re-framing throughout.\n\nResponse:\nThank you for highlighting this detail, which represents the broader implication of our study and aligns with its central focus. We have revised the final sentence of the abstract to become “The rarity of Burgess Shale-type ……and bridges the gap between traditional Ediacara-type preservation, Ediacara-type preservation with organic remains, and Burgess Shale-type preservation”.\n\nReviewer #3 (Remarks to the Author):\n\nThe authors have dealt with two major issues raised by the reviewers. The quality of the illustrations is greatly improved and a new specimen added. The evidence for fractals is difficult to demonstrate but is now much clearer. The taxonomic assignments are more generalized to reflect the nature of the material.\n\nThe authors have added EDS data (Figure S7 and Table 1). Table 1 provides weight per cent data but there is no information in Methods indicating whether these are based on the area mapped or spot samples.\n\nResponse:\nWe appreciate you pointed out this detail. We have added this information at the end of Methods section: “All sites were defined with a uniform area of approximately 1.12 mm x 0.84 mm, the data of which are presented in Table 1. An additional site, the fourth site, outlined with a red box in each specimen (Supplementary Fig. 7A, L), displays the difference in elemental distribution between the frond body and the matrix.”. In the caption of Table 1, we also added the following sentence “All sites, including site 1, site 2, and the matrix, were retrieved from a uniform area”.\n\nUnfortunately Figure S7 includes maps of one site on each specimen only whereas three were mapped. It would be useful to include the maps for the other areas (particularly the matrix). Needless to say maps convey different information to weight percent data, specifically element distribution, and overlap of different elements provides an indication of the minerals present.\n\nResponse:\nThank you for pointing out this issue. We have conducted an additional EDS analysis that includes both the fossil body and the matrix in each elemental map, which are now showing in the new Supplementary Figure S7. The information related to Table 1 has also been updated in the method section to reflect the modifications made to Supplementary Figure S7.\nTo preserve the specimen in its original state for further analysis, we avoided coating the specimen. However, this resulted in severe charging issue during SEM imaging. Thus, the overlapping elemental maps filed to clearly display the element distribution. For this reason, only individual elemental maps are provided.\n\nGiven that the EDS data are important to the interpretation of the preservation (BST-type or not) that information should be moved from Discussion to Results. Note that the high concentration of Fe in the body fossil does not, per se, indication exceptional preservation, and the evidence for pyrite is weak at best: Fe and S coincide somewhat in Figure S7 C and K, but not in N and V (indeed S is essentially absent in V). Likewise the fact that the lithology is dominated by silicates does not allow a silica (i.e. quartz) cement to be inferred: the silicates are presumably clays as petrography of the thin sections would confirm. A high concentration of P is mentioned (line 180) but there is no discussion of its significance and a map of P is omitted for the first frond specimen in Figure S7!\n\nResponse:\nBy following you suggestion, we have moved a part of the EDS content to the end of the results section: “EDS analyses of two frond specimens, ESEN 0017 and ESEN 0019a, display high concentrations of C and Fe in the body fossils, which contrast with the high concentrations of Mg, Al, K, Ti, and Ba in the matrix (Table 1, Supplementary Fig. 7). In both specimens, Si and O exhibit similar concentrations in both the fossil body and the matrix. Specimen ESEN 0017 (Supplementary Fig. 7A) has a higher concentration of S in the fossil body, whereas specimen ESEN 0019a (Supplementary Fig. 7L) has a higher concentration of P (Table 1, Supplementary Fig. 7)”.\nIn the new analysis, Fe and S in specimen ESEN 0017 (Fig. S7A) are matching with each other, but this relationship is still unclear in specimen ESEN 0019a (Fig. S7L). In the Table 1, ESEN 0019a (Fig. S7L) has a high concentration of S in the matrix, whereas ESEN 0017 (S7A) shows a high concentration of S in the frond body, consistent with the results in figures S7C, K, N, and V. In summary, the new maps displayed in Figure S7 are consistent with the data summarized in Table 1.\nAn explanation about the lower concentration of S observed in the analysis is provided in the Supplementary discussion: “During subsequent weathering, original pyrites could form iron oxides and, at the same time, the sulfuric acids released due to this alteration were washed away. This explains the lower content of S detected in the body fossils and the reddish color of the fossils.”,\nWe have deleted the content about the silicate cementation from both the main text and the supplementary discussion. Confirming this mechanism requires further study, as it demands substantially more evidence, including the point you have mentioned.\n“P” was not detected in the first fond specimen, ESEN 0017 (Supplementary Fig. S7A; Table 1). That is why there is no “P” elemental map for this specimen. We also expanded the discussion to include phosphate content. New text--“The high concentration of P in the specimen ESEN 00191a (Table 1, Supplementary Fig. 7L) provides additional chemical evidence for the early diagenetic mineralization of soft tissues43. Phosphatization preserves tissues with extremely high fidelity but is a strongly biased taphonomic process affected by factors such as size and environment44, 45. Decay of the small-sized frond may produce a suitable microenvironment for the process of phosphatization.”--has been added to lines 194-200.\n\nGiven the thickness of the silt laminae (Figure S8) it is hard to imagine rapid burial of in situ fronds.\n\nResponse:\nIn well-known Lagerstatten, thickness of silt laminae (or event beds) can also be very thin, with some reaching millimeter-scale thickness (i.e., fig. 1e, f in Caron et al. 2014, Nature Communications, 3210; supplementary fig. 1B in Fu et al. 2019, Science, 1338-1342; fig. 5A in Zhao et al. 2009, Palaios, 826-839). All these conditions are indicative of rapid burial. In addition, a few more observations are available from the thin-sections of Tongshan rock samples. 1) The thickness of silt laminae is different from bed to bed, indicating different durations of silt deposition. 2) Clay-beds and silt-beds alternate with each other, indicating the presence of cyclic events. 3) The boundaries between clay-beds and silt-beds are very sharp, indicating that silt beds entombed the lower living community of organisms, creating a clear separation from the overlying living community. These data support rapid burial of the Tongshan materials.\nSince there are no distinct transportation marks near the silt-rich beds, combined with other organismal evidence, we had concluded that the burial is in situ. Here, we accommodated your concern by adopting the phrasing “….rapid, likely in situ burial” in the text.\n\nThe message in Figure S10 is not clear (to this reviewer at least). BST preservation is already included in the Ediacaran in MacGabhann's original (2014) diagram, which is identical to A here, so what does this figure add.? And coloring most the Ediacaran in green in B obscures information rather than adding to it.\n\nResponse:\nWe have modified the caption of Figure S10, with new text marked with a yellow background. In the revised caption, we define the Figure A as “the traditional view of Ediacara Biota” and the Figure B as “the new view of Ediacara Biota”.\nFigure S10A, the original work in MacGabhann (2014), is used to provide a clear contrast with the new Figure S10B, which shows that both mouldic and BST preservations are the general preservation style of the Ediacara Biota. In figure S10B, this change causes the original yellow color in Figure A to be replaced with dark green (or chartreuse), represented by number “6” (Ediacaran fossils with both mouldic and BST preservations). Although the yellow area (i.e. mouldic preservation) in Figure B is reduced, the original information (i.e. both mouldic and BST preservations represented by number 6) in the Figure A is actually expanded. Expanding the Ediacara-type preservation with BST preservation in the Ediacara Biota represents a central argument of our study.\n\nFinally, even though the authors have removed mention of 'original' chemical composition Reviewer 3's concerns about the inclusion of phrases such as 'informative repository of tissue and integument composition' and 'compositional information in both chemical and morphological aspects' remain. This issue needs to be clarified so that it is obvious that what is meant is the composition of the fossils, not the composition of the original tissues. This confusion is exemplified in the authors' response where they state that 'In contrast, in BST preservation, the spine or claw can show multiple internal structural layers (e.g., Hallucigenia sparsa in Smith and Ortega-Hernandez, 2014, Nature, 514, 363-366), which can further be distinguished based on their chemical compositions, appearing as dark- and light-colored regions.' That paper includes no chemical data and it is very unlikely that the dark and light colored regions differ significantly in either their original (presumably chitin-protein) or diagenetically altered state.\n\nResponse:\nWe agree with you that it should be the composition of the fossils. Following your comments regarding the “composition” issue and incorporating with Reviwer2’s feedback, we have modified the last sentence of abstract to: “The rarity of Burgess Shale-type ……and bridges the gap between traditional Ediacara-type preservation, Ediacara-type preservation with organic remains, and Burgess Shale-type preservation”. We believe this change better highlights the broader significance of this work."}, {"round": 3, "reviewer_comments": {"reviewer_2": "My only further suggestion is to consider whether there are similarities to Cambrian fronds and to provide a reference to previous work that has identified fronds in BST preservation modes. The classic reference, for example is Conway Morris, S (1993) Ediacaran-like fossils in Cambrian Burgess Shale-type faunas of North America. Palaeontology 36, 593–635. This was also recently reviewed in Hoyal Cuthill, J.F., 2022. Ediacaran survivors in the Cambrian: suspicions, denials and a smoking gun. Geological Magazine, 159(7), pp.1210-1219.", "reviewer_3": "The authors have addressed the concerns of this reviewer."}, "author_response": "1 Manuscript ID: NCOMMS-25-02355-A\n\nWe appreciate your mention of both papers. Some BST-preserved fronds occur in the Cambrian, but they are widely regarded as Ediacaran-like fronds or problematica. For this reason, using the preservation of debated Cambrian organisms to discuss typical Ediacaran fronds is neither adequate nor convincing. This is also one of the reasons the discovery of the Tongshan Lagerstatte is significant. To provide a clear clarification, we added the following text in the section (Expansion of the Ediacaran Biota with Burgess Shale-type preservation) : Some BST fronds preserved in the Cambrian, which lack typical characters such as first- and second-order branches, are cautiously described as Ediacaran-like fronds57 or problematica58. The preservation of these debated Cambrian organisms58, 59 fails to provide solid evidence for the preservation of those typical Ediacara fronds.”\n\nThe detailed comparison between the Ediacaran-like fronds in the Cambrian and Tongshan materials requires further study, which is beyond the scope of our current work. However, following your suggestion, we made a further conclusion regarding this discovery. We added “as well as between the Ediacaran-like fronds in the Cambrian and typical Ediacaran fronds.” in the sentence “The material described here extends documentation of BST-style preservation into other elements of the Ediacara Biota, demonstrating a continuation from the Cambrian organisms to the Lantian Biota14, 64 as well as between the Ediacaran-like fronds in the Cambrian and typical Ediacaran fronds.”.\n\nIn this revision, we cited three more references.\n57. Conway Morris S. Ediacaran-like fossils in Cambrian Burgess Shale-type faunas of North America. Palaeontology 36, 593–635 (1993).\n\n58. Hu S, Zhao F, Liu AG, Zhu M. A new Cambrian frondose organism:‘Ediacaran survivor’or convergent evolution? J Geol Soc 180, jgs2022–2088 (2023).\n\n59. Hoyal Cuthill JF. Ediacaran survivors in the Cambrian: suspicions, denials and a smoking gun. Geol Mag 159, 1210–1219 (2022)."}]

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