Lei Zhang

Shan Chang

Mats Can Chen

E Eriksson

Qinglai Feng
email: qinglaifeng@cug.edu.cn

Maliha Michael Steiner

Zareen Khan

Jean Vannier

Marie-Béatrice Forel

Sébastien Clausen

Mats E Eriksson

Diverse cuticular remains in Cambrian (Series 2) SSF assemblages from China and the pioneer metazoan colonization of offshore environments

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The well-preserved 'Orsten'-type fossils are generally preserved in three-dimensions by secondary phosphatization, do not exceed 2 mm in size, and render fine anatomical details [START_REF] Walossek | Cambrian 'Orsten'-type arthropods and the phylogeny of Crustacea[END_REF][START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF]. Although their original organic compounds (e.g. chitin, collagen), and most of their inner tissues and ultrastructure (e.g. layers, [START_REF] Crowe | Echiniscus viridis (Tardigrada): Fine structure of the cuticle[END_REF] have been lost through decay and diagenetic processes, they retain exceptionally well-preserved details of their external anatomy and micro-ornamentation (e.g. polygonal patterns, [START_REF] Stankiewicz | Animal cuticles[END_REF][START_REF] Butterfield | An early Cambrian radula[END_REF][START_REF] Butterfield | Small carbonaceous fossils (SCFs): a new measure of early Paleozoic Paleobiology[END_REF]. The first 'Orsten'-type fauna was discovered by Klaus J. Müller (see [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF], from limestone nodules of the Alum Shale Formation of Sweden. In the 1980s and 1990s, studies of 'Orsten'-type fossils mainly focused on arthropods (especially crustaceans, [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF], allowing accurate reconstruction of the 3D-morphology and developmental stages of numerous Cambrian meiobenthic species (see discussion in [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF].

Since the mid-1990s, 'Orsten'-type preservations have been continuously documented globally, and their age has been further expanded to include the early Ordovician, lower Cambrian, and even the Ediacaran [START_REF] Zhang | Middle Cambrian arthropod embryos with blastomeres[END_REF][START_REF] Walossek | On the Cambrian diversity of Crustacea[END_REF]Dong et al., 2005aDong et al., , 2005b;;[START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF]Liu and Zhang, 2017). With the discovery of fossil metazoan embryos from the Doushantuo and Kuanchuanpu formations of China, embryology became a new topic in palaeontology [START_REF] Bengtson | Fossilized metazoan embryos from the earliest Cambrian[END_REF][START_REF] Bailey | Evidence of giant sulphur bacteria in Neoproterozoic phosphorites[END_REF][START_REF] Cohen | Large spinose microfossils in Ediacaran rocks as resting stages of early animals[END_REF][START_REF] Huldtgren | Fossilized nuclei and germination structures identify Ediacaran "animal embryos" as encysting protists[END_REF][START_REF] Cunningham | Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians[END_REF][START_REF] Yin | New observations of the ornamented Doushantuo embryo fossils from the Ediacaran Weng'an Biota, South China[END_REF][START_REF] Zhang | Triggers for the Cambrian explosion: hypotheses and problems[END_REF][START_REF] Yin | Early Cambrian animal diapause embryos revealed by X-ray tomography[END_REF].

In the 21th century a series of new discoveries have been made which bracket the critical time interval of the Cambrian bioradiation event [START_REF] Waloszek | The 'Orsten' window-a three-dimensionally preserved Upper Cambrian meiofauna and its contribution to our understanding of the evolution of Arthropoda[END_REF]Dong et al., 2005aDong et al., , 2005b;;[START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF][START_REF] Zhang | A eucrustacean metanauplius from the Lower Cambrian[END_REF]. For example, [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF]; [START_REF] Zhang | The first stalk-eyed phosphatocopine crustacean from the Lower Cambrian of China[END_REF] reported the oldest crown crustaceans and other panarthropod fossils of the Cambrian Epoch 2 in Yunnan Province, South China. Equally important are the phosphatic fossils reported from the Kuanchuanpu Formation in southern Shaanxi Province, China (e.g. [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF][START_REF] Zhang | A eucrustacean metanauplius from the Lower Cambrian[END_REF][START_REF] Zhang | Armored kinorhynch-like scalidophoran animals from the early Cambrian[END_REF][START_REF] Han | Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)[END_REF]. The 535-million-year-old Kuanchuanpu assemblages contain abundant animal remains with putative cnidarian affinities [START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF][START_REF] Wang | Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms[END_REF][START_REF] Shao | The Fortunian (lowermost Cambrian) Qinscyphus necopinus (Cnidaria, Scyphozoa, Coronatae) underwent direct development[END_REF] and diverse scalidophorans (Liu et al., 2014a;[START_REF] Steiner | The developmental cycles of early Cambrian Olivooidae fam. nov. (? Cycloneuralia) from the Yangtze Platform (China). Palaeogeogr., Palaeoclimat[END_REF][START_REF] Zhang | Armored kinorhynch-like scalidophoran animals from the early Cambrian[END_REF][START_REF] Shao | New material of the oldest known scalidophoran animal Eopriapulites sphinx[END_REF][START_REF] Shao | macrobenthic cycloneuralians from the Fortunian (lowermost Cambrian) of South China[END_REF][START_REF] Han | Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)[END_REF][START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF][START_REF] Wang | Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms[END_REF]. These have, in addition to the Burgess Shale-type fossils, significantly broadened our understanding of the Cambrian bioradiation.

Based on perceived differences in style of preservation, the 'Orsten'-Lagerstätten have been further sub-divided into an 'Orsten'-type preservation sensu stricto and sensu lato [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF] or 'Orsten'-type and Doushantuo-type preservations, see [START_REF] Butterfield | Exceptional fossil preservation and the Cambrian explosion[END_REF][START_REF] Xiao | Surfing in and on microbial mats: Oxygen-related behavior of a terminal Ediacaran bilaterian animal[END_REF][START_REF] Bottjer | Comparative taphonomy and phylogenetic signal of phosphatized Weng'an and Kuanchuanpu Biotas[END_REF]. The majority of 'Orsten'-type fossils sensu stricto was obtained from Cambrian limestone nodules interbedded with rich black shales. By contrast, the 'Orsten'-type fossils sensu lato were mostly found from Ediacaran to earliest Cambrian phosphatic rocks [START_REF] Xiao | Fossil preservation in the Neoproterozoic Doushantuo phosphorite Lagerstätte. South China[END_REF][START_REF] Chen | The sudden appearance of diverse animal body plans during the Cambrian explosion[END_REF], phosphatic limestone, dolostones [START_REF] Bengtson | Fossilized metazoan embryos from the earliest Cambrian[END_REF][START_REF] Steiner | New Early Cambrian bilaterian embryos and larvae from China[END_REF][START_REF] Steiner | The developmental cycles of early Cambrian Olivooidae fam. nov. (? Cycloneuralia) from the Yangtze Platform (China). Palaeogeogr., Palaeoclimat[END_REF] or cherts [START_REF] Hua | Skeletogenesis and asexual reproduction in the earliest biomineralizing animal Cloudina[END_REF]. As the studies progressed, the difference between the two types of preservation became less distinct [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF][START_REF] Han | Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)[END_REF]. In addition, the vertical distribution and quality of preservation of 'Orsten'-type and Doushantuo-type fossils turned out to be roughly similar [START_REF] Dornbos | Phosphatization through the Phanerozoic[END_REF]. Therefore, [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF] suggested that they should all united within a single category, the 'Orsten'-type fossils, defined by their size range and secondary phosphatization, irrespective of their age or host rock lithology [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF]. Putative embryos have previously been reported from the Shuijingtuo Formation in the eastern Three Gorges area, South China [START_REF] Broce | Possible animal embryos from the lower Cambrian (Stage 3) Shuijingtuo Formation, Hubei Province, South China[END_REF]. 'Orsten'-type fossils described here have been recovered from calcareous nodules of the upper Shuijingtuo Formation, in the same area. These assemblages consist of a wide variety of microscopic fragments showing highly diverse micro-ornamentation structures, as well as arthropod compound eyes, limbs, trunks and eggs. The sampled strata belong to the Cambrian Series 2, Stage 3, based on the associated trilobites and SSF biostratigraphy [START_REF] Zhang | Influence of palaeo-redox and diagenetic conditions on the spatial distribution[END_REF], and thus contemporaneous with the Chengjiang Biota and the 'Orsten'-type crustaceans from the Yu'anshan Formation in Yunnan Province [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF][START_REF] Zhang | A eucrustacean metanauplius from the Lower Cambrian[END_REF][START_REF] Zhang | The first stalk-eyed phosphatocopine crustacean from the Lower Cambrian of China[END_REF]. Seventeen different micro-ornamentation patterns are recognized on the surface of these cuticular fragments. Some of them are tentatively assigned to specific animal groups known from elsewhere in the Cambrian and other time periods, allowing a preliminary estimate of the diversity of the communities. Compared to complete specimens, which usually provide diagnostic features (e.g. [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF], fragmented specimens are often neglected by scientists working on 'Orsten'-type fossils (but see also [START_REF] Castellani | Exceptionally well-preserved isolated eyes from Cambrian 'Orsten' fossil assemblages of Sweden[END_REF]. However, recent studies have demonstrated their importance to formulate hypotheses on the origin of moulting [START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF] and the relationships between epidermis and cuticle [START_REF] Wang | Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms[END_REF]. Thus, although difficult to unambiguously attribute to specific taxa, these materials may provide new insights to the early evolution of the metazoans, as well as the offshore colonization by early animals during the Cambrian Bioradiation [START_REF] Li | Early Cambrian metazoan fossil record of South China: Generic diversity and radiation patterns[END_REF][START_REF] Fu | The Qingjiang biota-A Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China[END_REF].

Geological setting

All fossils reported here were collected from the Qiaojiaping section which is located in the eastern Three Gorges area, Hubei Province, China. During the early Cambrian, the South China Craton was an isolated microcontinent located at mid-northern latitudes, with the Yangtze Block in the northwest and Cathaysia Block in the southeast (modern coordinates, Fig. 1A; [START_REF] Li | Assembly, configuration, and break-up history of Rodinia: a synthesis[END_REF]. The two blocks were separated by the deep-water Jiangnan ocean basin. The Three Gorges area was located in median position within the Yangtze Platform, which developed as a southwest-northeast epeiric carbonate platform during early Cambrian times (Fig. 1B, [START_REF] Wang | History of Neoproterozoic rift basins in South China: implications for Rodinia break-up[END_REF]. The studied eastern Three Gorges area has recently been interpreted as recording transitions from carbonate epicontinental platforms and isolated carbonate platforms developed on palaeohighs (uplifts) to deeper intra-platform depressions or basins [START_REF] Chen | Main geological factors controlling shale gas reservoir in the Cambrian Shuijingtuo Formation in Yichang of Hubei Province as well as its and enrichment patterns[END_REF]. According to this model, the eastern Three Gorges area records more precisely a transition from nearshore to clastic intra-platform basin.

At the Qiaojiaping section, the lower Cambrian succession includes, in stratigraphical order, the upper Yanjiahe, Shuijingtuo and Shipai formations (Fig. 1C). The upper Yanjiahe Formation consists of clastic dolostone interbedded with black shales. Disconformably overlying the Yanjiahe Formation, the Shuijingtuo Formation (ca. 46 m thick) can be subdivided into four beds, in ascending order: (i) Bed 1 (7.2 m thick) dominated by medium-bedded black shales containing abundant limestone nodules and intercalations of black limestone beds; (ii) Bed 2 (25.7 m thick) is composed of medium-bedded black marls; (iii) Bed 3 (3.5 m thick) is composed of thin-bedded, carbonaceous black shales containing limestone nodules; (iv) Bed 4 (10 m thick) is composed of thick-bedded muddy limestones intercalated with thin-bedded black marls that pass laterally into interbedded grayish-black to purple muddy shales (Zhang et al., 2018a). The overlying Shipai Formation at the Qiaojiaping section is dominated by mudstone interbedded with siltstone (see fig. 2 in [START_REF] Chang | New probable cnidarian fossils from the lower Cambrian of the Three Gorges area, South China, and their ecological implications[END_REF]. The 'Orsten'-type fossil bearing Bed 3 is dominated by planar laminations and lacks cross laminations, which is consistent with deposition just below the storm wave-base. Neither horizontal nor vertical burrows are present in these black shales.

The Yanjiahe Formation most probably ranges from the E-C transition to the Cambrian Stage 2 [START_REF] Ishikawa | Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: prominent global-scale isotope excursions just before the Cambrian Explosion[END_REF][START_REF] Guo | Small shelly fossils from the early Cambrian Yanjiahe Formation, Yichang, Hubei, China[END_REF][START_REF] Ahn | Lowermost Cambrian acritarchs from the Yanjiahe Formation, South China: implication for defining the base of the Cambrian in the Yangtze Platform[END_REF][START_REF] Chang | The Ediacaran-Cambrian rise of siliceous sponges and development of modern oceanic ecosystems[END_REF][START_REF] Steiner | Cambrian small skeletal fossil and carbon isotope records of the southern Huangling Anticline, Hubei (China) and implications for chemostratigraphy of the Yangtze Platform. Palaeogeogr., Palaeoclimat[END_REF]. Due to the occurrence of earliest trilobites of the Tsunyidiscus biozone, the Shuijingtuo Formation is assigned to the Cambrian Stage 3 (of Series 2) of the provisional stratigraphic framework [START_REF] Steiner | Neoproterozoic to early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China). Palaeogeogr., Palaeoclimat[END_REF][START_REF] Dai | Ontogeny of the Eodiscoid Trilobite Tsunyidiscus acutus from the lower Cambrian of South China[END_REF][START_REF] Peng | The Cambrian Period[END_REF]. The Shipai Formation mostly spans two trilobite zones, namely the lower Redlichia meitanensis and the upper Palaeolenus lantenoisi zones [START_REF] Zhang | Armored kinorhynch-like scalidophoran animals from the early Cambrian[END_REF]. Thus, the Shipai Formation could be constrained to the Cambrian Stage 4 of the provisional stratigraphic framework [START_REF] Peng | The Cambrian Period[END_REF].

Material and methods

A total of 140 rock samples (each approx. 5 kg) were collected from the upper Shuijingtuo Formation in the Three Gorges area and were processed by acid digestion. Limestone samples were broken into pieces of about 100 cm 3 and digested into 7% acetic acid at room temperature. Calcium acetate (20 g per kg of rocks) was added to the solution to protect fossils from excessive etching. Sample residues were rinsed through 2 mm and 0.054 mm meshes and dried at room temperature every two weeks. The fossils were hand-picked under a binocular microscope and selected specimens were mounted on a copper stub using a double-sided adhesive tape and coated with gold or carbon (latter for analytic purposes). The morphology and chemical composition of the fossils were analyzed using a Quanta 200 Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS) and a Field Emission Scanning Electron Microscope (Zeiss Sigma 300 FESEM) at the State Key Laboratory of Geological Process and Mineral Resources (GPMR) at China University of Geosciences (Wuhan), China. All figured specimens are housed in the collection at School of Earth Sciences, China University of Geosciences (Wuhan), Wuhan, P.R. China.

Results

Acid digestion of limestone nodules from the upper Shuijingtuo Formation yielded abundant SSFs, eodiscoid trilobites, phosphatic fragments and some undetermined fossilized soft tissues, including muscle fibers. The SSFs recovered from the limestone nodules are generally replicated, filled or replaced by calcium phosphate or silicified phosphate, whereas the phosphatic fragments are mainly preserved in the form of calcium phosphate [START_REF] Yue | Embryonic and post-embryonic development of the Early Cambrian cnidarian Olivooides[END_REF]. In addition to these phosphatic fragments, other 'Orsten'-type specimens were recovered from the Shuijingtuo Formation, including arthropod trunks (Fig. 2A), putative eggs (Figs. 2B, 2C), exoskeletons of juvenile bivalved arthropods (Fig. 2D), stalked compound eyes with ommatidia (Figs. 2G, 2H; [START_REF] Castellani | Exceptionally well-preserved isolated eyes from Cambrian 'Orsten' fossil assemblages of Sweden[END_REF] and appendages (Fig. 2J; [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF]Zhai et al., 2019). Similar fragments have also been reported from other 'Orsten'-type fossil Lagerstätten such as that of the Alum Shale Formation of southern Sweden (the Guzhangian Stage of the Cambrian Series 3 and the Furongian; [START_REF] Castellani | Exceptionally well-preserved isolated eyes from Cambrian 'Orsten' fossil assemblages of Sweden[END_REF]. The phosphatic fragments generally display a great variety of surface micro-ornamentations. Some of them show a variable degree of crumpled, twisted and curved features, which might represent intact or decomposed soft parts of organisms rather than biomineralized exoskeletons. Generally, these types of fragments only replicated the micro-ornamentation patterns on one side of the specimens only, whilst arthropod fragments remains show ornamentation patterns on both sides. Most of the ornamented fragments display a consistent uniform pattern on their surface. In total, seventeen (n=17) different types of ornamentation patterns were recognized. Although some of the ornamented patterns identified herein are known from fossil specimens found elsewhere (e.g. [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF][START_REF] Butterfield | An early Cambrian radula[END_REF], most of them have not been reported before. Detailed descriptions of the different patterns are presented below.

Morphological description of the specimens

All measurements are provided in Table 1. Description.

-Variably sized, low relief, palm print-like lattice, sometimes bearing spines on the surface or edge (Figs. 2K, 2L, 3A-3D, 7A-7I); lattices are particularly elongated on specimens shown in Fig. 3A (ca. 12-126 μm for different specimens in Figs. 3A, 3B, 7A, 7B) compared to those of other specimens (ca. 14 μm in maximal length for the specimen in Fig. 2K, ca. 12 μm in maximal length for the specimen in Fig. 2L, and ca. 15 μm in maximal length for the specimen in Figs. 3C,7G) and the shape of the polygons shows considerable variation over the surface. Similar lattice micro-ornamentation can also be seen on the surface of some appendages (e.g. Fig. 2L). The surface of exceptionally preserved specimens is sometimes wrinkled. Conical spinescovered by the lattice patternextend perpendicular to the tips of the short conical spines (ca. 36 μm in length of the spines) which are hollow.

Material examined. -2 fragments of arthropod appendages, 15 cuticle fragments.

Remarks. -Although micro-ornamentations vary in shape and size, specimens assigned to Pattern A seem to belong to a single taxon. Because the structures of Pattern A occur on the surface of an appendage (Fig. 2L), these cuticular elements are assigned to arthropods. They might belong to eodiscoid trilobites, bradoriids or bivalved arthropods, because similar lattices can sometimes be observed on the surface of contemporaneous species in South China (e.g. fig. 10 in [START_REF] Zhang | Moult stages and dimorphism of Early Cambrian bradoriids from Xichuan, Henan, China[END_REF]fig. 3B in Butterfield, 1990;fig. 4 in Haug et al., 2014;fig. 7 in Broda and Zatoń, 2017;Figs. 10-11 in this study).

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Pattern B is characterized by polygons (ca. 24 μm in maximal length). Generally, it consists of pentagons and hexagons separated by two parallel walls or lattices (about 1 μm thick, Figs. 7J,7K). The walls are weakly elevated but not flat. Variably sized palm print-like lattices are present in the polygons. Irregular lace-like structures are visible within the polygons, which might represent cell moulds. These laces are sometimes perforated, and may represent taphonomic artefacts rather than original features (Fig. 7K).

Material examined. -2 specimens.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Fragments with Pattern C ornament are smooth and characterized by relatively large pentagons or hexagons (ca. 40 μm in maximal length, Fig. 3G) separated by low relief ridges. One specimen (Fig. 3H), which lacks distinct ridges, might be the negative mould of surface structures. They are considered herein as Pattern C with specific ornamentation defined by the size of the polygons (40 μm in maximal length for Fig. 3G and 39 μm for Fig. 3H). One specimen with Pattern C ornamentation shows numerous circular pits with a diameter of about 1.5 μm (Figs. 7M,7N). The size and morphology of the pits suggest that they might be cell moulds (see Fig. 7N).

Material examined. -2 specimens.

Remarks. -The characteristics of the polygons and ridges remarkably recall those of Pattern A, but the size of the former is much larger. Specimens with Pattern C ornamentation probably belong to arthropods as similar structures can be seen on the carapace of some bivalved arthropods, such as Isoxys and Tuzoia [START_REF] Fu | Ontogeny and dimorphism of Isoxys auritus (Arthropoda) from the Early Cambrian Chengjiang biota, South China[END_REF][START_REF] Wen | Morphology and ontogeny of Tuzoia bispinosa from the Kaili Biota (Cambrian Stage 5) of eastern Guizhou, China[END_REF].

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Due to incomplete replication, micro-ornamentations are only visible in a small area of a single specimen. Boundaries have no relief. Pattern D is composed of regu larly distributed polygons (ca. 23 μm in maximal length) with indistinct boundaries, resulting in an overall structure with complex polyhedron appearance (Fig. 7O). The surface of all polygons is smooth. No finer micro-ornamentation occurs within the polygons. Material examined. -One specimen.

Remarks. -The only fragment with Pattern D polygonal ornament, preserving a strait linear structure similar to a dorsoventrally compressed hinge line, is interpreted herein as derived from a bivalve arthropod.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description.

-Pattern E is characterized by a network of polygonal walls delimiting convex, almost hemispheric, lenticular surfaces (the polygons and lenticulars are ca. 9 μm in width; Fig. 8A). Polygonal walls are very regular, and resemble honeycombs. These lenticular structures are hollow, as can be observed in fractured areas (Fig. 8A). Such a micro-ornament only occurs in a certain area of the specimen and gives room to irregular stripe structures elsewhere (Fig. 3J).

Material examined. -One specimen.

Remarks.

-The lenticular structure of this specimen strongly resembles those of the compound eyes of arthropods. However, a clear compound eye structure (e.g. globular or convex shape eyeball, optic stalk, etc, cf. Figs. 2G,2H) is lacking here.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Fragments with Pattern F are characterized by subparallel straight ridges separating deep, relatively wide (about 50-100 μm in width) furrows with concave floor. The furrows are covered with small, irregular, sub-polygonal ornament (about 25 μm in width; Figs. 8C). Rounded pores are evenly distributed within the furrows. The larger ones (up to 55 μm in diameter) are bounded by up to ten rows of deformed polygons/folds forming a variably extended, invagination or collar. Most of the smaller pores (maximal diameter ca. 12 μm) regularly appear adjacent to the large ones, but some are independently scattered on other parts of the cuticle (Figs. 8C).

Material examined. -2 specimens.

Remarks. -The furrows described in Pattern F are comparable to the annuli observed on the cuticle of segmented worms [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF]. Pores of various size, sometimes with short and inward extended collars, might correspond to partially degraded setae, parapodia or appendages of vermiform fossils [START_REF] Müller | Palaeoscolecid worms from the middle Cambrian of Australia[END_REF]. The three features (closely spaced annuli, circular hollows and polygonal structures) together suggest that the cuticle remains of Pattern F might be assigned to Palaeoscolecida, an extinct group of scalidophoran worms with a worldwide distribution and well represented in both Burgess Shale-and 'Orsten'-type Lagerstätten [START_REF] Glaessner | Lower Cambrian Crustacea and annelid worms from Kangaroo Island, South Australia[END_REF][START_REF] Hou | Palaeoscolecid worms may be nematomorphs rather than annelids[END_REF][START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF]. The precise relationship of the Palaeoscolecida to the priapulids or alternatively the nematomorphs remains under discussion, but it is suggested that their systematic position is within the superphylum Ecdysozoa (moulting invertebrate animals, [START_REF] Ivantsov | Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia[END_REF]. Microplates and/or platelets are typical of palaeoscolecids. The platelets were either originally absent, or secondary lost from our specimens. Limited preserved features preclude any further assignment to any palaeoscolecid species.

Occurrence Remarks.

-The specimen with ornament Pattern G is a phosphatic steinkern, partly enveloped by a cuticle. The spine differs from those observed in specimens showing an ornament pattern of type A. Although some vermiform ecdysozoans have similar spines and surface patterns (e.g. Zhang et al., 2018b), no accurate assignment to this group is possible.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description.

-Pattern H consists of an irregular network of narrow (about 2 μm), sharp furrows delimiting polygonal areas. The center of these areas can be flat (Figs. 4E,8G), perforated by subcircular pores bordered by rounded rims (Fig. 4D), or occupied by a variably developed convex pock, sometimes perforated at its apex (Figs. 4E,8F).

Material examined. -3 specimens.

Remarks. -Similar pock-marked cuticles have also been found in Small Carbonaceous Fossils (SCFs) from the Burgess Shale and, the early Cambrian Mahto Formation, (Alberta, Canada) and the Kaili Lagerstätte (Guizhou Province, South China) (see figs. 9.1-7 in [START_REF] Butterfield | An early Cambrian radula[END_REF]fig. 7S in Harvey et al., 2012). On the specimens described by Butterfield (2008, fig. 9), the pock-marks are characterized by a thickened, more or less circular, sometimes lozenge-shaped rim features, similar to the rim observed herein around pores. The perforations may result from the taphonomic process [START_REF] Butterfield | An early Cambrian radula[END_REF]. The elements described by [START_REF] Butterfield | An early Cambrian radula[END_REF] were interpreted as belonging to a molluscan radula. Indeed some features closely resemble those found in extant aplacophoran molluscs. The pock-marked cuticle is interpreted as having supported multiple biomineralized sclerites/spines in the manner of a modern chiton girdle [START_REF] Butterfield | An early Cambrian radula[END_REF]. The similar ornament seen in our specimens may belong to a similar radula-like organ as well.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -The lattice of Pattern I is characterized by a network of fine, narrow, straight ridges surrounding flat, irregularly polygonal areas (up to 16.47 μm in width; Figs. 4F,8H). Star-shaped (Fig. 8H) to rounded knobs (Fig. 8H) are formed at some intersections between ridges. They seem to preferentially occupy multiple-intersections, between more than 4 ridges, triple points generally lacking a knob-structure. The maximal diameter of the knobs is 5.65 μm. The length of the polygon segment ranges from 8 to 20 μm.

Material examined. -2 specimens.

Remarks. -Similar structures occur in arthropods such as eodiscoid trilobites (Figs. 4G, 8I, 11) and the bradoriid Kunmingella xiaoyangensis (see Plate 6, fig. 8 in [START_REF] Zhang | Phosphatized bradoriids (Arthropoda) from the Cambrian of China[END_REF]. Our cuticle fragments are therefore tentatively interpreted as derived from arthropods.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -A thin, elevated ridge can be observed in the middle of the specimen with Pattern J. Rhombic depressions (ca. 30 μm in maximal length) separated by the ridge are present along the external surface of the cuticular fragment; in places, the rhombic structures appear to gradually deform into fish scale-like depressions (Figs. 8J,8K).

Material examined. -One specimen.

Remarks. -SSFs such as Rhombocorniculum (see figs. 46-48 in [START_REF] Kouchinsky | An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia[END_REF], Mongolitubulus or Rushtonites, have a similar ornamentation pattern and might belong to the spines of hallucigeniid lobopodians (see SCFs described in [START_REF] Caron | Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians[END_REF] or eodiscoid trilobites [START_REF] Li | Microstructure and functional morphology of the Early Cambrian problematical fossil Rhombocorniculum[END_REF]. However, the ornament in Hallucigenia, Mongolitubulus and Rushtonites generally displays cone-in-cone structures, which are resulting from the retention of moulted cuticular elements [START_REF] Caron | Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians[END_REF]. Our specimens are also much larger than those described in [START_REF] Caron | Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians[END_REF], but indeed are very similar to the specimens shown in [START_REF] Kouchinsky | An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia[END_REF]figs. 46-48).

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Pattern K is strongly folded, and wrinkled, covered by a fine fishnet-like structure (Fig. 8L). No small-scale ornamented features are visible due to folding, crumpling and poor preservation. However, Pattern K differs from all other ornamented types.

Material examined. -3 specimens.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description.

-The single specimen with Pattern L has two adjacent layers that probably represent the external and internal layer of fossil fragment (Fig. 5A). This pattern consists of irregularly tessellated polygonal elements (microplates; about 22 μm in maximal width). The microplates have a concave surface, interpreted herein as the outer surface (Fig. 8M), which is bounded by a smooth to faintly pustulose ridge. The layer beneath is generally smooth. Convex structures can be found on its surface. It might be the prints of polygonal microplates.

Material examined. -One specimen.

Remarks. -The microplates on this specimen resemble the cuticular plates seen on the annuli of ecdysozoans. In particular, similar tessellation can be observed on the trunk of palaeoscolecid worms [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF][START_REF] Ivantsov | Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia[END_REF]. The double layer may represent exfoliation of the outer layer of the cuticle (figs. 2.5, 2.6 in [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF], or most probably the two surfaces of a partially preserved folded and flattened cuticle.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -M-type specimens have a curled shape and show transverse ripples. The M ornamentation pattern consists of densely packed, irregularly anastomosing (or bifurcating) ripples. Ripples have a regular transverse, rounded shape. Drop-shaped pits, bounded by ripples, are irregularly distributed on the cuticle surface (Fig. 8N). Pits diameter is ca. 8 μm and the spacing between the pores is ca. 30-50 μm.

Material examined. -3 specimens.

Remarks. -Pattern M resembles the ornament found on certain cuticular areas of Yicaris. Yicaris is the earliest crown crustaceans reported from the contemporaneous Yu'anshan Formation (Series 2, Stage 3) in Yunnan Province, South China [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF]. The legs of the anomalocaridid Cucumericrus decoratus also bear comparable ornament [START_REF] Hou | The Cambrian fossils of Chengjiang, China: the flowering of early animal life[END_REF].

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Fragments with N Pattern are weakly twisted. A ridge line can be observed in at least three specimens, which generally a fold along this line. Pattern N is characterized by transverse serrate terraces (Figs. 5C,5D), which are distributed in regular, concentric parallel rows. Small tips occur on the terraces (Fig. 8O). The distance between those tips is generally constant (16 and 31 μm). The surface between the two adjacent terraces is smooth.

Material examined. -5 specimens.

Remarks. -Pattern N differs from Pattern M by having more regular transverse stripes. Cuticular terraces are found in a number of arthropod groups in which they have evolved independently (e.g. [START_REF] Schmalfuss | Structure, patterns, and function of cuticular terraces in recent and fossil arthropods[END_REF][START_REF] Schmalfuss | Structure, patterns and function of cuticular terraces in trilobites[END_REF]. Remarks.

-Similar pits and polygons can be observed on the surface of the phosphatic shell of some bradoriids (Liangshanella, Fig. 10). Some of these features have been interpreted as the possible boundaries of epithelial cells that secreted the cuticle (e.g. brachiopods; Zhang et al., 2016a), although a specific taxon is impossible to assign.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description.

-Remains with Pattern P are flat to irregularly folded. Bimodal pits are evenly distributed on the surface of these fragments: the smaller pits are almost isometric, flat, hemispherical and ca. 6 μm in diameter (Fig. 9K); the larger ones are more irregular in shape, and more sparsely distributed with a diameter of ca. 24 μm (Fig. 9J).

Material examined. -2 specimens.

Remarks. -Comparable features occur in acrotretid brachiopods or hyoliths that have been interpreted as cell boundaries (Zhang et al., 2016b(Zhang et al., , 2018b)). Regular hemispheric pits appear to be closely related to the epithelial cell moulds on some acrotretid brachiopods or hyoliths (Zhang et al., 2016b(Zhang et al., , 2018b)). However, those latter pits are all of the same size (Zhang et al., 2016b(Zhang et al., , 2018b)). Shells of tannuolinid tommotids are penetrated by regular tubules. Regularly distributed pores can be observed in tannuolinids, but they are generally deeper [START_REF] Skovsted | Tommotiids from the early Cambrian (Series 2, Stage 3) of Morocco and the evolution of the tannuolinid scleritome and setigerous shell structures in stem group brachiopods[END_REF].

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Description. -Remains with Pattern Q consists of numerous tightly packed and linearly arranged nodes (Fig. 6F). Nodes have an irregular, polygonal to subcircular shape and a flat top surface. The height of these nodes is relatively uniform with variable lengths (maximal length ca. 9 μm). Some conical, crater-like, higher structures with a central pit sparsely protrude between the nodes (Figs. 9M,9N). The diameter of these cones is around 15 μm.

Material examined. -2 specimens.

Remarks. -The Pattern Q has never been described in any Orsten specimens. It is therefore impossible to attribute it to any known clade.

Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Discussion

Origin of ornamented fragments?

Although represented by fragments, these fossil assemblages from the upper Shuijingtuo Formation are remarkable by the diversity of their ornamentation patterns and the quality of their preservation. However, their biological affinities are difficult to determine because i) most of the micro-ornamentation patterns here have never been described in whole or larger body fossils; ii) trunks, heads or appendages to which these cuticular fragments may have belonged, are missing, and; iii) external ornamentation patterns cannot be used as accurate diagnostic features as shown by extant arthropods from different groups which share comparable cuticular ornament (e.g. polygons, nodes, pits, etc).

Although micro-ornamentation in animals often finds its origin in self-organized processes, it acquired various ecological functions through evolution. The cuticle of many Cambrian and extant ecdysozoans acts as an interface between the body and the surrounding environment and for this reason, plays an important role in several vital functions, such as protection (from physical damage and predators) and locomotion, and also accommodates sensory organs (e.g. infaunal worms; Brad bury and [START_REF] Bradbury | Principles of animal communication[END_REF][START_REF] Stankiewicz | Animal cuticles[END_REF]Yang and Sun, 2006;[START_REF] Neville | Biology of the arthropod cuticle[END_REF][START_REF] Pérez-De La Fuente | Early evolution and ecology of camouflage in insects[END_REF][START_REF] Broda | A set of possible sensory system preserved in cuticle of Late Devonian thylacocephalan arthropods from Poland[END_REF][START_REF] Manukyan | A living mesoscopic cellular automaton made of skin scales[END_REF]. Micro-reticulation patterns (polygonal structures) represent one such example. The cuticle is secreted from underlying epithelial cells and, in ecdysozoans (Scalidophora, Nematoida, Panarthropoda), is renewed periodically via ecdysis [START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF][START_REF] Wang | Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms[END_REF]. In many ecdysozoan groups, the external reticulated ornament faithfully replicates the boundaries of the epithelial cells [START_REF] Zhang | Middle Cambrian arthropod embryos with blastomeres[END_REF][START_REF] Yang | Ecdysis in a stem-group euarthropod from the early Cambrian of China[END_REF][START_REF] Wang | Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms[END_REF]. Polygonal structures arose independently in many Cambrian animal groups (cuticle sensu lato, such as mollusks, brachiopods and hyoliths [START_REF] Parkhaev | New data on the morphology of ancient gastropods of the genus Aldanella Vostokova, 1962 (Archaeobranchia, Pelagielliformes)[END_REF][START_REF] Parkhaev | Protoconch morphology and peculiarities of the early ontogeny of the Cambrian helcionelloid mollusks[END_REF]Zhang et al., 2016bZhang et al., , 2018c;;[START_REF] Li | Shell microstructures of the helcionelloid mollusc Anabarella australis from the lower Cambrian (Series 2) Xinji Formation of North China[END_REF], which provides little taxonomic specificity. Reticulated patterns also can be found in a variety of non-metazoan organisms, including acritarch vesicles preserved as organic-walled fossils [START_REF] Xiao | Fossil preservation in the Neoproterozoic Doushantuo phosphorite Lagerstätte. South China[END_REF][START_REF] Su | Zircon SHRIMP U-Pb ages of tuff in the Tieling Formation and their geological significance[END_REF][START_REF] Xiao | Phosphatized acanthomorphic acritarchs and related microfossils from the Ediacaran Doushantuo Formation at Weng'an (South China) and their implications for biostratigraphic correlation[END_REF][START_REF] Agić | Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton -A window into the early eukaryote evolution[END_REF]. Numerous embryos also have a polygonal pattern due to dividing blastomeres [START_REF] Yin | New observations of the ornamented Doushantuo embryo fossils from the Ediacaran Weng'an Biota, South China[END_REF][START_REF] Broce | Possible animal embryos from the lower Cambrian (Stage 3) Shuijingtuo Formation, Hubei Province, South China[END_REF]. The size of these polygons, whether they correspond to cell boundaries or result from other processes, often varies according to their location on the surface of organisms and/or the ontogenetic stages (e.g. [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF][START_REF] Waugh | Ontogenetic variations in cuticle morphology in the blue crab Callinectes sapidus Rathbun, 1896[END_REF]Zhang et al., 2016b). There is no fundamental differences between the size of polygonal patterns in acritarchs, embryos and the cuticular fragments described herein (Fig. 13, see also [START_REF] Yin | New observations of the ornamented Doushantuo embryo fossils from the Ediacaran Weng'an Biota, South China[END_REF][START_REF] Broce | Possible animal embryos from the lower Cambrian (Stage 3) Shuijingtuo Formation, Hubei Province, South China[END_REF][START_REF] Agić | Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton -A window into the early eukaryote evolution[END_REF]. The unimodal size distribution of polygonal structures is therefore probably not a practical guide for distinguishing species.

Acritarchs have developed diverse ornamentations such as polygonal structures, spines, microgranulae etc (e.g. Liu et al., 2014a). The ornament of some of the fossils described herein may be compared with that of the large acanthomorphic accritarchs [START_REF] Xiao | Fossil preservation in the Neoproterozoic Doushantuo phosphorite Lagerstätte. South China[END_REF][START_REF] Su | Zircon SHRIMP U-Pb ages of tuff in the Tieling Formation and their geological significance[END_REF][START_REF] Xiao | Phosphatized acanthomorphic acritarchs and related microfossils from the Ediacaran Doushantuo Formation at Weng'an (South China) and their implications for biostratigraphic correlation[END_REF][START_REF] Agić | Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton -A window into the early eukaryote evolution[END_REF]. However, i) the large acanthomorphic acritarchs became instinct by the early Cambrian Stage 3 [START_REF] Yin | The early evolution of the acanthomorphic acritarchs in China and their biostratigraphical implication[END_REF], and; ii) the large acanthomorphic acritarchs fall within the range of a few hundred microns [START_REF] Xiao | Fossil preservation in the Neoproterozoic Doushantuo phosphorite Lagerstätte. South China[END_REF][START_REF] Su | Zircon SHRIMP U-Pb ages of tuff in the Tieling Formation and their geological significance[END_REF][START_REF] Xiao | Phosphatized acanthomorphic acritarchs and related microfossils from the Ediacaran Doushantuo Formation at Weng'an (South China) and their implications for biostratigraphic correlation[END_REF][START_REF] Agić | Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton -A window into the early eukaryote evolution[END_REF], which is much smaller than most of our fossil remains. Similarly, most embryos from the Ediacaran and Cambrian reach a few hundred microns [START_REF] Yin | Early Cambrian animal diapause embryos revealed by X-ray tomography[END_REF]. The ornamented fragments described herein are therefore interpreted as metazoan cuticles or associated tissues (in particular epithelial). They share numerous common features with ecdysozoans (such as the pavement of epithelial cells, sensory pores, etc), which are recorded from the early Cambrian [START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF][START_REF] Wang | Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms[END_REF]. Moreover, they seem to be dominated by ecdysozoans sensu lato, since micro-reticulated networks and microplates are found in, for example, both arthropods and scalidophorans; e.g. [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF][START_REF] Dornbos | Phosphatization through the Phanerozoic[END_REF][START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF]. Possible affinities with arthropods, palaeoscolecid worms [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF], acrotretid brachiopods (epithelial cells, Zhang et al., 2016a), mollusks [START_REF] Butterfield | An early Cambrian radula[END_REF] are proposed in the systematic section.

The Burgess Shale preservation generally obscures micro-ornamentation (because of compression and diagenesis, [START_REF] Gaines | Mechanism for Burgess Shale-type preservation[END_REF]. This is not the case in Orsten-type assemblages in which small organisms or fragments are secondarily phosphatized, leading to exquisite 3D-preservation of mostly cuticularized body-parts [START_REF] Butler | Experimental taphonomy of Artemia reveals the role of endogenous microbes in mediating decay and fossilization[END_REF][START_REF] Liu | New material of three-dimensionally phosphatized and microscopic cycloneuralians from the Cambrian Paibian Stage of South China[END_REF]. Thus, fossil cuticles have great potential to provide important information on the ecology, cellular structure of internal tis sues and growth mode of ancient animals [START_REF] Zhang | Early Cambrian palaeoscolecid cuticles from Shaanxi, China[END_REF][START_REF] Castellani | Exceptionally well-preserved isolated eyes from Cambrian 'Orsten' fossil assemblages of Sweden[END_REF]. In this context, 'Orsten'-type fossil Lagerstätten have attracted increasing attention because they capture fine details of external features that are rarely preserved in Burgess Shale-type fossils, where the organic cuticles are often replaced by aluminosilicates or iron minerals [START_REF] Gaines | Mechanism for Burgess Shale-type preservation[END_REF].

U N C O R R E C T E D P R O O F L. Zhang
The cuticular remains described here reveal a faunal assemblage with a relatively high diversity, probably dominated by ecdysozoans (scalidophorans and panarthropods, Fig. 12, Table 1). However, to which species, genus or suprageneric categories these fragments belong remains uncertain. Yet, the only way to identify these fragments would be to assign them to more complete specimens found either in the same formation or elsewhere.

U N C O R R E C T E D P R O O F

Modes of fossil preservation and Cambrian bioradiation

The emergence of metazoans is one of the major events in the history of life that took place during the Ediacaran-Cambrian transition. It revolutionized the global ecosystems, and eventually gave rise to the present-day biological and ecological diversity (e.g. [START_REF] Bengtson | Origins and early evolution of predation[END_REF][START_REF] Conway-Morris | Darwin's dilemma: the realities of the Cambrian 'explosion[END_REF][START_REF] Chen | The sudden appearance of diverse animal body plans during the Cambrian explosion[END_REF]. Major anatomical, functional and behavioral innovations occurred during this time interval, which led to an increased complexity of ecological interactions (e.g. food webs), as well as the expansion of ecological space [START_REF] Maloof | The earliest Cambrian record of animals and ocean geochemical change[END_REF][START_REF] Benton | Constraints on the timescale of animal evolutionary history[END_REF][START_REF] Wood | First macrobiota biomineralization was environmentally triggered[END_REF]. These major events are mainly based on various fossil evidence from Ediacaran to Ordovician Lagerstätten (e.g. [START_REF] Jago | The Emu Bay Shale lagerstätte: a history of investigations[END_REF][START_REF] Caron | A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies[END_REF][START_REF] Paterson | The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana[END_REF][START_REF] Hou | The Cambrian fossils of Chengjiang, China: the flowering of early animal life[END_REF][START_REF] Fu | The Qingjiang biota-A Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China[END_REF][START_REF] Harper | The Sirius Passet Lagerstätte of North Greenland: a remote window on the Cambrian Explosion[END_REF]. SSFs also provide a wealth of information about the early evolution of metazoans. Yet, due to taphonomic bias and the patchiness of fossil record, the basal animal tree is still far from being understood (e.g. [START_REF] Harvey | Exceptionally preserved Cambrian loriciferans and the early animal invasion of the meiobenthos[END_REF]. Molecular clocks and biomarkers provide independent estimates for the timing of animal origin and early diversification, and suggest that the divergence of major phyla occurred much earlier than the Ediacaran [START_REF] Erwin | The Cambrian conundrum: early divergence and later ecological success in the early history of animals[END_REF][START_REF] Rota-Stabelli | Molecular timetrees reveal a Cambrian colonization of land and a new scenario for ecdysozoan evolution[END_REF][START_REF] Reis | Uncertainty in the timing of origin of animals and the limits of precision in molecular timescales[END_REF][START_REF] Parry | Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil[END_REF]. It has been suggested that most progenitors of Cambrian animals were probably meiofaunal [START_REF] Brown | Man is but a worm: chordate origins[END_REF][START_REF] Laumer | Spiralian phylogeny informs the evolution of microscopic lineages[END_REF][START_REF] Wray | Molecular clocks and the early evolution of metazoan nervous systems[END_REF][START_REF] Han | Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)[END_REF][START_REF] Harvey | Exceptionally preserved Cambrian loriciferans and the early animal invasion of the meiobenthos[END_REF]. If so, their tiny size and lack of hard skeletal parts may have dramatically reduced their chance of being fossilized, resulting in virtually no fossil record and therefore in a considerable gap between molecular clock estimates and the fossil records for the deep-time splits in the animal tree [START_REF] Donoghue | The origin and early evolution of chordates: molecular clocks and the fossil record. Telling the evolutionary time: molecular clocks and the fossil record[END_REF][START_REF] Cunningham | The origin of animals: can molecular clocks and the fossil record be reconciled?[END_REF][START_REF] Parry | Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil[END_REF].

Phosphatized soft tissue preservation, occurring from the Ediacaran to the earliest Ordovician, has provided another remarkable window into the early evolution of metazoans [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF][START_REF] Bottjer | Comparative taphonomy and phylogenetic signal of phosphatized Weng'an and Kuanchuanpu Biotas[END_REF]. The oldest secondarily phosphatized metazoans, including embryo-like fossils with a variety of cleavage patterns (Yin et al., 2016), possible post-embryonic stage of gemmules and adult animals, occur in the ca. 610 million-year-old, Weng'an Biota from China ('Orsten'-type preservation sensu lato, [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF]; but also see [START_REF] Bottjer | Comparative taphonomy and phylogenetic signal of phosphatized Weng'an and Kuanchuanpu Biotas[END_REF][START_REF] Du | Potential Ediacaran sponge gemmules from the Yangtze Gorges area in South China[END_REF][START_REF] Yin | Sponge grade body fossil with cellular resolution dating 60 Myr before the Cambrian[END_REF]. Compared to the Burgess-type faunas and SSF assemblages, 'Orsten'-type Lagerstätten have the particular advantages to favor the preservation of tiny animals such as the meiofauna. However, ecdysozoans and cuticular remains of possible ecdysozoans origin are virtually absent from the Ediacaran 'Orsten'-type Lagerstätten [START_REF] Schiffbauer | Exceptional fossil conservation through phosphatization[END_REF]. The 'Orsten'-type fossil record of ecdysozoans becomes frequent at the base of the Cambrian, as illustrated by the ca. 535 Ma old Kuanchuanpu Formation in southern Shaanxi Province [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF][START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF]Liu et al., 2014bLiu et al., , 2017;;[START_REF] Schiffbauer | Exceptional fossil conservation through phosphatization[END_REF][START_REF] Zhang | Armored kinorhynch-like scalidophoran animals from the early Cambrian[END_REF]Zhang et al., 2016a;[START_REF] Han | Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)[END_REF]. Cuticular remains attributed to ecdysozoans become abundant and diverse in Cambrian Series 2 (e.g. [START_REF] Zhang | An epipodite-bearing crown-group crustacean from the Lower Cambrian[END_REF][START_REF] Zhang | The first stalk-eyed phosphatocopine crustacean from the Lower Cambrian of China[END_REF]this study), which corresponds to the first peak of the ecdysozoan bioradiation recorded by other types of fossils [START_REF] Li | Early Cambrian metazoan fossil record of South China: Generic diversity and radiation patterns[END_REF]. 'Orsten'-type fossils and other sources of valuable information obtained from SSFs, SCFs and BST-type Lagerstätten, when put together, shed light on the early evolutionary steps of early animal life (e.g. [START_REF] Harvey | Exceptionally preserved Cambrian loriciferans and the early animal invasion of the meiobenthos[END_REF][START_REF] Daley | Early fossil record of Euarthropoda and the Cambrian Explosion[END_REF][START_REF] Bottjer | Comparative taphonomy and phylogenetic signal of phosphatized Weng'an and Kuanchuanpu Biotas[END_REF].

Metazoan offshore invasion

According to multiple paleo-redox reconstructions of marine settings based on elemental and isotopic proxies, the early Cambrian Epoch 2, Age 3 ocean was stratified, with heterogeneous oxygenation (Cheng et al., 2017;[START_REF] Li | Coupled oceanic oxygenation and metazoan diversification during the early-middle Cambrian?[END_REF][START_REF] Li | Assembly, configuration, and break-up history of Rodinia: a synthesis[END_REF][START_REF] Zhang | Heterogenous oceanic redox conditions through the Ediacaran-Cambrian boundary limited the metazoan zonation[END_REF]Zhang et al., 2018a;[START_REF] Zhang | Influence of palaeo-redox and diagenetic conditions on the spatial distribution[END_REF]. A decrease in faunal diversity from shallow to deep environments is in line with the oxygenation gradient in South China [START_REF] Li | Early Cambrian metazoan fossil record of South China: Generic diversity and radiation patterns[END_REF]. Therefore, the offshore invasion of metazoans during this interval is likely to have been controlled by the oxygenation conditions in the water column [START_REF] Canfield | Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life[END_REF][START_REF] Lyons | The rise of oxygen in Earth's early ocean and atmosphere[END_REF][START_REF] Zhang | Triggers for the Cambrian explosion: hypotheses and problems[END_REF][START_REF] Chen | Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals[END_REF]Li et al., 2017;[START_REF] Liu | New material of three-dimensionally phosphatized and microscopic cycloneuralians from the Cambrian Paibian Stage of South China[END_REF]Zhang et al., 2018a[START_REF] Zhang | Influence of palaeo-redox and diagenetic conditions on the spatial distribution[END_REF]. However, exceptions may occur as exemplified by bed 3 of the Qiaojiaping section from which diverse fossil cuticles are reported from limestone nodules (present study, Fig. 14). The studied interval of the Qiaojiaping section was deposited in an offshore environment of the Yangtze Platform (Zhang et al., 2020, Fig. 14). The paleo-redox proxies obtained from bed 3 in the closely located Luojiacun section, indicate that the bottom water was strongly depleted in oxygen (anoxic-suboxic to euxinic; Zhang et al., 2018b) during Cambrian Series 2, Stage 3 (Fig. 14). This is consistent with sedimentological observations, such as the high carbonaceous content, dominance of horizontal lamination or parallel bedding, and absence of bioturbation. In modern oceans, assemblages from poorly oxygenated areas are generally low in diversity, and dominated by small, unmineralized organisms [START_REF] Bowyer | Controls on the evolution of Ediacaran metazoan ecosystems: a redox perspective[END_REF]. Very few organisms are able to live in or close to the sediment-water interface in the absence of dissolved oxygen [START_REF] Danovaro | The first metazoa living in permanently anoxic conditions[END_REF]. The diverse assemblages described here are found in assumed anoxic-suboxic to euxinic depositional environments (Zhang et al., 2018c). Meiofauna, which live in interstitial microenvironments between sand grains where water circulates, can survive in oxygen-depleted or anoxic conditions (e.g. [START_REF] Danovaro | The first metazoa living in permanently anoxic conditions[END_REF]. The 'Orsten'-type assemblages from the Alum Shale Formation in Southern Sweden mainly consist of autochthonous (and paraautochtonous) tiny arthropods and allies interpreted as epibenthic organisms which inhabited diverse niches within the unconsolidated, flocculent detrital zone above the poorly oxygenated (dysoxic to anoxic) seafloor [START_REF] Müller | A remarkable arthropod fauna from the Upper Cambrian "Orsten" of Sweden[END_REF][START_REF] Tang | Orsten deposits from Sweden: Miniature late Cambrian arthropods[END_REF][START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF][START_REF] Maeda | Cambrian Orsten Lagerstatte from the Alum Shale Formation: Fecal pellets as a probable source of phosphorus preservation[END_REF]. The average size of the specimens investigated here (e.g. Fig. 2J), if complete, would fall outside the range of the meiofauna (from 32 μm to 1,000 μm in size according to [START_REF] Giere | Meiobenthology: the microscopic motile fauna of aquatic sediments[END_REF][START_REF] Parry | Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil[END_REF]. In addition, phosphatized carapaces of Isoxys (Fig. 2I ited more oxygenated waters in adjacent areas, either in the middle-upper part of the water column and/or at the water sediment interface [START_REF] Jin | Spatiotemporal variability of ocean chemistry in the early Cambrian, South China[END_REF]Zhang et al., 2018b). After death, the pelagic organisms would have settled on the sea floor, whereas epibenthic elements would have been transported from their original habitat by storm events or turbidity currents [START_REF] Maeda | Cambrian Orsten Lagerstatte from the Alum Shale Formation: Fecal pellets as a probable source of phosphorus preservation[END_REF]Fu et al., 2019, Fig. 14). Generally, soft carcasses decompose extremely fast after death under oxygenated conditions [START_REF] Eriksson | Internal soft-tissue anatomy of Cambrian 'Orsten' arthropods as revealed by synchrotron X-ray tomographic microscopy[END_REF][START_REF] Eriksson | Baring it all: undressing Cambrian'Orsten' phosphatocopine crustaceans using synchrotron radiation X-ray tomographic microscopy[END_REF][START_REF] Murdock | Decay of velvet worms (Onychophora), and bias in the fossil record of lobopodians[END_REF]Zhang et al., 2016b;[START_REF] Harper | The Sirius Passet Lagerstätte of North Greenland: a remote window on the Cambrian Explosion[END_REF]. Incomplete phosphatization of carcasses may have led to fragmentation without current intervention [START_REF] Maas | The 'Orsten'-more than a Cambrian Konservat-Lagerstätte yielding exceptional preservation[END_REF]. The lack of evidence for obrution and major periodic sediment inputs such as tempestites in bed 3 of the Shuijingtuo Formation suggests that transportation should have been very limited. It should be noted that these two possibilities (meiofauna v.s. transportation) are not mutually exclusive. The fossil assemblages may come from different sources (Fig. 14). Whatever their origin (meiofaunal and/or pelagic animals), we suggest that the cuticular fossil elements from Shuijingtuo Formation are mostly autochthonous or parautochthonous (Fig. 14). Current views hold that the peak of metazoan diversification was slightly delayed in offshore settings compared to nearshore areas [START_REF] Li | Coupled oceanic oxygenation and metazoan diversification during the early-middle Cambrian?[END_REF][START_REF] Zhang | Influence of palaeo-redox and diagenetic conditions on the spatial distribution[END_REF]. However, our results are consistent with recent studies that described highly diversified marine faunas in relatively deeper-water depositional areas, typically the Qingjiang Lagerstätte that is supposed to be even more diverse than the Chengjiang Lagerstätte [START_REF] Fu | The Qingjiang biota-A Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China[END_REF][START_REF] Zhang | Influence of palaeo-redox and diagenetic conditions on the spatial distribution[END_REF]. The abundant and diverse cuticles reported herein could suggest that the invasion of metazoans into offshore environments closely followed, or was even simultaneous to, their radiation in shallower water equivalents.

Conclusions

A variety of 'Orsten'-type fossils are described here from the upper Shuijingtuo Formation (eastern Three Gorges area, China; Cambrian Series 2, Stage 3). They are mainly represented by fragments deposited in a relatively deep shelf setting. At least seventeen ornamentation patterns are recognized on these fragments. Most of them are cuticular remains of ecdysozoans animals such as arthropods and palaeoscolecid worms; others may belong to brachiopods and/or mollusks. The original habitat of these organisms remains uncertain. Some of them may have lived within the water column and sank down to the bottom after death, while others (e.g. epibenthic species) may have been transported and fragmented by currents to be eventually accumulated in the depositional area. Some may also be partly preserved cuticles, i.e. resulting from an incomplete phosphatization of more complete carcasses. The diverse cuticles provide a coherent picture of the Cambrian bioradiation recorded by the 'Orsten'-type and other preservations. The new fossil material would indicate animals colonized off-shore environments very shortly after and even during the animal biodiversification. The largest proportion correspond to the most common member in the assemblage (e.g. Pattern O is more abundant than other types), whilst the smallest proportions represent the minorities of the assemblage. Note that the proportion is only approximate because most of the specimens are somehow twisted and folded which made the accurate measurement a very hard task. See original quantitative data in Table 1.

Fig. 1 .

 1 Fig. 1. A. Palaeogeographic reconstruction of South China during the early Cambrian (after[START_REF] Hou | The Cambrian fossils of Chengjiang, China: the flowering of early animal life[END_REF][START_REF] Fu | The Qingjiang biota-A Burgess Shale-type fossil Lagerstätte from the early Cambrian of South China[END_REF]. B. Geological map of the Three Gorges area, Hubei Province (after[START_REF] Guo | Discovery of protoconites genus from Yanjiahe Formation Terreneuvian of the Three Gorge area, South China[END_REF]. C. Position of the 'Orsten'-type fossils discovered from the Shuijingtuo Formation at the Qiaojiaping section.

Fig. 2 .

 2 Fig. 2. Selected fossils extracted from concretions of the upper Shuijingtuo Formation, Three Gorges area, South China. A. Trunk segment of an arthropod. B-C, putative eggs. D. juvenile specimen of a tentative arthropod. E-F. Uncertain tissues, probably related to putative muscle strands (compare with Briggs, 2003, fig 2a). G-H, Compound eyes of arthropods, G1, close-up of G; H1, close-up of H. J, Arthropod exopod. I, Fragment of the bivalved arthropod Isoxys. K-L, cuticle Pattern A. K, No. 17Q-SJT-3001/012. K1, detail of K, showing fine polygonal structures distributed on the surface of the body and small conical spines. L, No. 17Q-SJT-3001/052; L1, detail of L, showing fine polygonal structures distributed on the surface of the appendages and extended to the top of the spines. Scale bar 100 μm for all specimens, unless otherwise specified.

  U N C O R R E C T E D P R O O F L.Zhang et al. Palaeogeography, Palaeoclimatology, Palaeoecology xxx (xxxx) xxx-xxx

Fig. 3 .

 3 Fig. 3. Cuticle patterns A-F. Specimens are from the Shuijingtuo Formation. A-D, Pattern A. A, No. 1811Q-SJT-408/001; B, No. 17Q-SJT/942; C, No. 17Q-SJT-1/013; D, No. 18Q-S-408/ 041. E-F, Pattern B. E, No. 17Q-SJT-1000/179; F, No. 1811Q-SJT-408/090. G-H, Pattern C. G, No. 17Q-SJT-1000/015; H, No. 17Q-SJT-1000/098. I, Pattern D, No. 1811Q-SJT-408/027. J, Pattern E, No. 17Q-SJT-1000/015. K, Pattern F, No. 18Q-SJT-408/081.larly visible in some areas (see Fig.8D). In other areas, it gradually changes into fine strip-like patterns (Fig.8E). A prominent cone-shaped spine, preserved as a possible steinkern, protrudes from the surface of the cuticle (ca. 253 μm

Fig. 4 .Fig. 5 .

 45 Fig. 4. Cuticle patterns F-K. Specimens are from the Shuijingtuo Formation. A, cuticle Pattern F, No. 18Q-SJT-2001/052. B, cuticle Pattern G, No. 1811Q-SJT-408/060. C-E, cuticle Pattern H. C, No. 17Q-SJT-JH1-3001/079; D, No. 17Q-SJT-JH1-3001/079; E, No. 18Q-SJT-JH29/011. F, cuticle Pattern I, No. 1811Q-SJT-408/067. G, exoskeleton of possible arthropods. No. 1811Q-SJT-408/047. H, cuticle Pattern J. No. 18Q-SJT-2001/036. I, cuticle Pattern K, No. 18Q-SJT-JH29/056.detailed diagnostic features precludes further taxonomic assessment.Occurrence. -Upper Shuijingtuo Formation, Cambrian Series 2, Stage 3.

Fig. 6 .

 6 Fig. 6. Cuticle patterns O-Q. Specimens are from the Shuijingtuo Formation. A-C, Pattern O. A, No. 17Q-SJT-3001/188; B, No. 18Q-S-408/092; C, No. 17Q-SJT-3001/126. D-E, Pattern P. D, No. 18Q-S-408/035; E, No. 1811Q-SJT-408/038. F, Pattern Q, No. 2018Q-SJT/004.

Fig. 7 .

 7 Fig. 7. Details of the cuticle patterns A-D. A, detail of Pattern A in Fig. 3A, showing fine polygonal structures. B, detail of Pattern A in Fig. 7A, showing elongated polygonal structures. C, detail of Pattern A in Fig. 3B, showing varying size of polygonal structures, and folded features of the cuticle. D, detail of Pattern A in Fig. 7C, showing twisted and folded features of the cuticle. E, detail of Pattern A in Fig. 3B, showing varying size of polygonal structures, twisted and folded features of the cuticle. F, detail of Pattern A in Fig. 7E, showing polygonal structures and uniform small size (< 1 μm) crystal grains distributed on the surface of the cuticle. G, detail of Pattern A in Fig. 3C, showing fine polygonal structures and conical spines; the broken part shows that the spine is hollow. H, detail of Pattern A in Fig. 3D, showing fine polygonal structures and wrinkled structures on the cuticle. I, detail of Pattern A in Fig. 3D, showing fine polygonal structures and wrinkled structures on the cuticle. J, detail of Pattern B in

Fig. 8 .

 8 Fig. 8. Details of the cuticle patterns E-N. A, detail of Pattern E in Fig. 3J, showing lenticular structure and high relief walls between the polygons. B, detail of Pattern F in Fig. 3K, larger hollows and sub-regular polygonal lattices on the surface. C, detail of Pattern F in Fig. 4A, showing annuli, larger and smaller hollows, and sub-regular polygonal lattices. D, detail of Pattern G in Fig. 4B, showing very fine reticulate lattices on the cuticle. E, detail of Pattern G in Fig. 4B, showing very fine reticulate lattices on the cuticle of Pattern G. F, detail of Pattern H in Fig. 4C, showing that the surface is characterized by variable sized pock-marks. G, detail of Pattern H in Fig. 4E, showing that this specimen is penetrated by sub-circular hollows of variable sizes. H, detail of Pattern I in Fig. 4F, showing the fine fishnet-like structure and knot-like intersections. I, detail of the exoskeleton of possible arthropods in Fig. 4G, showing exactly same fishnet-and knot-like structures as Fig. 4F. J, detail of Pattern J in Fig. 4H, showing rhom

Fig. 9 .

 9 Fig. 9. Details of the cuticle patterns O-Q. A, detail of Pattern O in Fig. 5E, showing the overall appearance of an orange peel and shallow pits. B, detail of Pattern O in Fig. 5F, showing the shallow pits. C, detail of Pattern O in Fig. 5G, showing polygons surrounded the pits. D, details of Pattern O in Fig. 5I, showing the overall appearance of an orange peel and circular pits. E, details of Pattern O in Fig. 9D, showing the overall appearance of an orange peel and circular pits. F, details of Pattern O in Fig. 6A, showing irregular pits and shallow grooves. G, details of Pattern O in Fig. 6C, showing irregular pits and shallow grooves on the surface of the Pattern O. H, details of Pattern P in Fig. 6D, showing evenly distributed bimodal pits on the surface of Pattern P. I, details of Pattern P in Fig. 6D, showing evenly distributed bimodal pits on the surface of Pattern P. Arrow in the figures 9I: a, creases which could be the trace of the exoskeleton; J, details of Pattern P in Fig. 6E, showing evenly distributed bimodal pits on the sur

Fig. 10 .

 10 Fig. 10. Fossil of the possible Liangshanella sp. (bradoriids) from the Shuijingtuo Formation in the studied. Two specimens from the same sample, sharing similar outlines and pits, but with slightly different polygonal patterns (see arrows in B1 and A2) on the surface of the shales. A, No. 17SPC-25-2/001, B, No. 17SPC-25-2/001.

Fig. 11 .

 11 Fig. 11. Trilobites from the Shuijingtuo and Shipai formations in the studied area, showing that there are different pattern of micro-ornamentation on their moulds. A. Pygidium of Tsunyidiscus acutus from the Shuijingtuo Formation, No. 17SPC-25-2/001; B-C. Cephalon of the Hubeidiscus orientalis, from the basal Shipai Formation, B, No. 17SPC-25-2/001, C, No. 17SPC-25-2/001; D-F, Cephalon of an undetermined trilobite, from the Shuijingtuo Formation, D, No. 17SPC-25-2/001, E, No. 17SPC-25-2/001, F, No. 17SPC-25-2/001.

Fig. 12 .

 12 Fig.12. Proportion of each ornamentation type in the cuticle assemblage. Each proportion depends on the size of the corresponding specimens as well as its frequency in the studied assemblage. The largest proportion correspond to the most common member in the assemblage (e.g. Pattern O is more abundant than other types), whilst the smallest proportions represent the minorities of the assemblage. Note that the proportion is only approximate because most of the specimens are somehow twisted and folded which made the accurate measurement a very hard task. See original quantitative data in Table1.

Fig. 13 .Fig. 14 .

 1314 Fig.13. Boxplots showing measurements of maximal size of polygons (A) and pits (B) on cuticles from the Cambrian (Series 2) Shuijingtuo Formation and comparison with similar patterns on shells, compound eyes, epithelial cell moulds found from the Shuijingtuo and Kuanchuanpu formations, showing that there is no clear boundary between the length, width and their ratio for most patterns except for the polygons which are particularly large or small. Cuticle fossils of scalidophoran worms from[START_REF] Wang | Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms[END_REF]. Original data of this figure can be found in Table1.

Table 1

 1 Statistics regarding the studied cuticles, fragmented arthropod, brachiopod moulds and polygons on acritarchs from the Cambrian Series 2 upper Shuijingtuo Formation.

	Cuticle Patterns	Specimens	Abbr. (see in Fig. 28)	Description of data		Number of measurements	Mean (μm)	Median (μm)	Min (μm)	Max (μm)	Standard deviation	Proportion of the surface (%)*
	Pattern A	specimen 1 (17Q-SJT-3001/052) specimen 2 (17Q-S-3001-012) specimen 3 (1811Q-SJT-408/001) specimen 4 (17Q-SJT/942) specimen 5 (17Q-SJT/942) specimen 6 (17Q-SJT-2000-1/ 013) specimen 7 (2018Q-SJT-2001/017) specimen 8 (17Q-SJT-3001/058) specimen 9 (17Q-SJT-3001/223) specimen 10 (17Q-SJT-408/ 041)	A1 A2 A3 A4 A5 A6 A7 A8 A9 A10	Maximum diameter of the polygons Maximum diameter of the polygons Distance between the spines Maximum diameter of the polygons Maximum diameter of the polygons Maximum diameter of the polygons Maximum diameter of the polygons Maximum diameter of the polygons Maximum diameter of the polygons Maximum diameter of the polygons Maximum polygons diameter of the	L L D L L L L L L L L	19 12 6 4 28 57 73 57 74 47 47	14.32 43.39 258.93 126.25 12.75 12.02 13.84 10.46 17.02 17.68 18.61	11.90 29.84 226.80 126.67 11.67 11.30 13.73 10.40 17.24 17.14 18.26	8.24 8.87 115.69 85.37 7.8 7.22 6.69 7.72 10.69 12.55 10.22	35.51 140.95 526.73 166.31 30.01 24.70 18.93 13.40 21.67 24.90 28.11	6.09 37.65 135.76 30.11 4.86 3.63 2.73 1.44 2.42 2.57 3.67	27.37

* The data shown in this column correspond to Fig.

12

. Proportion of the surface means proportion of the surface occupied by each type of ornamentation. Total area of the cuticles is 34.75 cm 2 . Wang, D., Vannier, J., Schumann, I., Wang, X., Yang, X.G., Komiya, T., Uesugi, K., Sun, J. and Han, J., 2019. Origin of ecdysis: fossil evidence from 535-million-year-old scalidophoran worms. Proceedings of the Royal Society B, 286, p.20190791.

Acknowledgments

This work was supported by National Natural Science Foundation of China (grants 41972024, 41430101, 41502014, 41890843). We thank Wei Guo and Yuhao Yi for their help with SEM work. Prof. Yunhuan Liu and Dr. Ben Yang are acknowledged for their detailed guidance during the chemical processes. Dr. Min Shi, Tao Dai, Deng Wang and Zhiliang Zhang are acknowledged for constructive discussions during the preparation of the manuscript. Special thanks are due to two anonymous reviewers for their constructive remarks on the manuscript. We thank the editor Prof. Thomas Algeo for editorial input.

Declaration of Competing Interest

The authors declared that they have no conflicts of interest to this work.


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