The central nervous system (CNS) presents unique insight into the behaviors and ecology of extant and extinct animal groups. However, neurological tissues are delicate and prone to rapid decay, and thus their occurrence as fossils is mostly confined to Cambrian Burgess Shale–type deposits and Cenozoic amber inclusions. We describe an exceptionally preserved CNS in the horseshoe crab Euproops danae from the late Carboniferous (Moscovian) Mazon Creek Konservat-Lagerstätte in Illinois, USA. The E. danae CNS demonstrates that the general prosomal synganglion organization has remained essentially unchanged in horseshoe crabs for >300 m.y., despite substantial morphological and ecological diversification in that time. Furthermore, it reveals that the euarthropod CNS can be preserved by molding in siderite and suggests that further examples may be present in the Mazon Creek fauna. This discovery fills a significant temporal gap in the fossil record of euarthropod CNSs and expands the taphonomic scope for preservation of detailed paleoneuroanatomical data in the Paleozoic to siderite concretion Lagerstätten of marginal marine deposits.The central nervous system (CNS) plays a critical role in animal functions, behavior, and ecology, and contains valuable morphological data that inform the evolution of complex organisms (Schmidt-Rhaesa et al., 2015). Although the lipid-rich composition of the CNS makes it prone to rapid decay (Sansom, 2016), recent research demonstrates that neurological tissues can be preserved as carbonaceous compressions in Cambrian animal macrofossils from open-marine deposits (Edgecombe et al., 2015; Strausfeld et al., 2016; Ortega-Hernández et al., 2019; Table S1 in the Supplemental Material1). Paleoneuroanatomical remains are extremely rare in younger deposits before Cenozoic ambers, leaving profound gaps in our understanding of CNS evolution. Notable exceptions include the putative brain described for the Carboniferous Tullimonstrum gregariumRichardson, 1966 (McCoy et al., 2016) and a phosphatized ventral nerve cord in a Triassic insect (Montagna et al., 2017), suggesting that paleoneuroanatomical structures can be captured by taphonomic pathways other than Burgess Shale–type preservation in the Paleozoic (Butterfield, 1995; Gaines, 2014), albeit extremely rarely.We describe an exceptionally well-preserved CNS in the belinurid Euproops danae (Meek and Worthen, 1865) from the Pennsylvanian (Moscovian) Mazon Creek Konservat-Lagerstätte in Illinois, USA. The discovery of paleoneuroanatomy in E. danae is significant because xiphosurids (horseshoe crabs) are the only wholly aquatic extant order of euchelicerates, and their fossil record is critical for reconstructing the complex evolutionary history of Euarthropoda (Lamsdell, 2016). Euproops danae shares similar prosomal appendage organization with the extant Limulus polyphemus (Linnaeus, 1758) (Haug and Rötzer, 2018) and is one of the best-documented fossil xiphosurids both within Mazon Creek (Raymond, 1945) and globally (Haug and Rötzer, 2018; Bicknell and Pates, 2020). Therefore, these new data on E. danae inform on the internal anatomy of this major euchelicerate group, represent the first occurrence of CNS preservation in a fossil horseshoe crab, and shed new light on preservational modes for fossilized neural tissue.We reviewed E. danae specimens in the Yale Peabody Museum (New Haven, Connecticut, USA) Division of Invertebrate Paleontology (YMP IP). One specimen (YPM IP 168040) showing evidence of preserved internal anatomy was identified. This specimen was photographed as a series of stacked images under normal LED light using a Canon EOS 5DS digital SLR camera fitted with a Canon MP-E 65 mm macro lens (complete specimen) and a Canon MP-E 65 mm 1×–5× macro lens (close-up on CNS) and a Cognisys StackShot 3X stacking system. Photos were stacked and stitched using Helicon Focus 7 (https://www.heliconsoft.com/heliconsoft-products/helicon-focus/). Backscatter and energy dispersive X-ray spectroscopy (EDS) analyses were conducted to examine composition of the CNS with a JEOL JSM-6010LA scanning electron microscope (SEM) under low vacuum at a voltage of 20 kV. The specimen was not coated.Specimen YPM IP 168040 contains the first known record of E. danae internal anatomy, aspects of which are preserved on both the part and counterpart (Fig. 1; Fig. S1 in the Supplemental Material). The specimen is a fully articulated individual in dorsal view, preserved with limited relief in a siderite concretion, as is typical for Mazon Creek fossils (Clements et al., 2019). The prosoma is 6.9 mm long and 16.8 mm wide, the opisthosoma is 7.3 mm long and 11.2 mm wide, and the telson is 7.9 mm long. Based on opisthosomal size, the specimen likely represents the third Euproops developmental stage (sensuHaug and Rötzer, 2018). The axial region of the prosoma features a bilaterally symmetrical complex structure with a white coloration (Figs. 1A, 1B, and 1G). Elemental mapping indicates that this feature is enriched in aluminum and silicon (Clements et al., 2019; Figs. 1I and 1J) and depleted in iron, potassium, and magnesium relative to the siderite matrix (Figs. 1H, 1M, and 1N). The morphology of the internal structure consists of a fusiform ring oriented along the sagittal axis with seven paired and regularly spaced lobe-like lateral extensions that generally increase in length posteriorly (Figs. 1B and 1D). Although the anterior-most third of the structure is broken and displaced laterally, there is direct continuity between the lateral extensions on both sides and the width of the aluminosilicates defining the ring boundaries. White coloration is also noted at the prosoma-opisthosoma and opisthosoma-telson articulations.The internal structure preserved in specimen YPM IP 168040 is morphologically comparable to the CNS of L. polyphemus early juveniles and more mature individuals, specifically the synganglion formed by the fusion of the segmental ganglia in the prosoma (Harzsch et al., 2005; Göpel and Wirkner, 2015; Fig. 1E). The seven paired lateral extensions correspond to the segmental nerves of the protocerebrum (optic nerves), deutocerebrum (chelicerae), four walking legs, and the pushing leg. The opening of the fusiform ring structure represents the esophageal foramen (Figs. 1B and 1D). There is no evidence of a preserved opisthosomal CNS in specimen YPM IP 168040. An alternative interpretation of the internal axial structure as a gut is discounted because the conspicuous opening corresponding to the esophageal foramen is a feature without an analogue in the euarthropod digestive tract, and the L. polyphemus gut lacks a metameric organization (Zacaï et al., 2016).Euproops danae offers valuable insights into the CNS of extinct euchelicerates. The correspondence between the synganglia of E. danae and L. polyphemus suggests close functional and behavioral similarities between modern and extinct xiphosurids, despite the substantial temporal and phylogenetic gaps between their respective clades (Bicknell and Pates, 2020). This fossil shows that the fundamental organization of the xiphosurid CNS has essentially remained unchanged for >300 m.y. Furthermore, close anatomical parallels between the CNS organization of L. polyphemus, E. danae, and the great appendage stem-group chelicerates (Tanaka et al., 2013; Ortega-Hernández et al., 2019) suggest that euchelicerates have sustained this conserved neuroanatomy since the Cambrian.This unique E. danae specimen represents the earliest unequivocal evidence of preserved euarthropod neuroanatomy from a brackish marginal-marine deposit (Clements et al., 2019). Elemental mapping indicates that the CNS—which is white in visible light (Fig. 1G)—is enriched in aluminum, silicon, and oxygen (Figs. 1I–1K). Further, SEM imaging reveals that vermiform stacks of platy, micron-sized crystallites compose the white material (Fig. 1F). These observations, coupled with depletion in potassium and magnesium relative to matrix, indicate that the white mineral highlighting the CNS is kaolinite.Kaolinite is well documented in Mazon Creek fossils (Baird et al., 1986; Cotroneo et al., 2016; Clements et al., 2019). It commonly occurs as a void-filling mineral that precipitated within concretion cavities. This includes voids inside fossils where bones had dissolved, where plant stems were carbonized and undergone volume loss, leaving spaces, and where aragonitic bivalve shells dissolved within the concretion matrix (Baird et al., 1986; Cotroneo et al., 2016; Clements et al., 2019). In Mazon Creek material, kaolinite is associated occasionally with sphalerite and galena, indicative of later-stage mineralization during burial (Keller, 1988), and more commonly with pyrite, which may form during early diagenesis or later mineralization. Based on these aspects of its occurrence, kaolinite in Mazon Creek fossils has been consistently interpreted as being late diagenetic in origin (Baird et al., 1986, 1997; Clements et al., 2019), precipitating in voids long after fossilization was complete.Morphology of kaolinite crystallites within the examined CNS (Fig. 1F) confirms the late-stage precipitate origin, consistent with previous interpretations. However, kaolinite was not a component of the original fossilization process that captured the paleoneuroanatomical information. Instead, kaolinite precipitated in a void that remained long after the decay of neural tissue. The CNS was therefore preserved originally as a mold, captured as minerals grew around the highly labile tissues prior to loss of structural integrity during decomposition. Elemental mapping (Figs. 1H–1N; Fig. S2) shows that the outer CNS margin is sharp and the matrix is composed of siderite, as indicated by enrichment in iron, carbon, and oxygen (Figs. 1H and 1K; Fig. S2). The siderite surrounding the CNS has the same composition and texture as the matrix of the concretion enveloping the specimen.The preservation of the examined CNS requires that siderite grew rapidly around the decomposing organism, molding the CNS in three dimensions. The CNS was then lost to decay, leaving a void inside its external mold that was stabilized by the siderite mineral matrix. This void was subsequently filled by the precipitation of kaolinite (Fig. 2). Such a pathway has two important implications.(1) The siderite matrix must have been emplaced very quickly to capture neural tissue. While this rapid growth could be difficult to account for (e.g., Berner, 1968; Yoshida et al., 2020), it is currently the accepted mode of exceptional preservation within the Mazon Creek Konservat-Lagerstätte (Clements et al., 2019). Such a preservational pathway is thought to have produced the flattened composite molds observed in the Mazon Creek concretions, particularly of dermal, cuticular, and other external structures (Baird et al., 1986; Clements et al., 2019). However, this pathway can also preserve more labile internal tissues, such as the observed CNS, which is very rare in Mazon Creek fossils. Rapid precipitation of the concretionary matrix is consistent with the notably narrow range of δ13C values reported from the fossiliferous concretions (Cotroneo et al., 2016). During prolonged concretion growth, changes in pore-water biogeochemistry due to exhaustion of oxidants and switching of primary bacterial metabolic pathways commonly result in pronounced variation in carbon isotope values across concretions from the center to the edge (Raiswell and Fisher, 2000). Although similarly suppressed δ13C variation might result from protracted pervasive growth, rather than from rapid concentric growth (Mozley and Burns, 1993), the robust molding of the CNS in siderite suggests rapid pervasive concretion growth is far more likely (Sellés-Martínez, 1996). The limited range of isotopic variation observed in Mazon Creek concretions is therefore noteworthy (Cotroneo et al., 2016) and supports rapid siderite development around decaying organisms.(2) CNS preservation by molding implies a loss of other soft tissues beneath the prosomal shield prior to CNS decay. In modern xiphosurids, the CNS is sheathed by a thick vascular membrane (Göpel and Wirkner, 2015). Such a membrane in E. danae may have slowed the decay of the synganglion (relative to other internal structures) and facilitated the rapid molding of these delicate tissues. Given the ferruginous pore-water conditions that led to the precipitation of siderite, it is also possible that dissolved Fe2+ may have played a role in delaying decay of neural tissue (Schweitzer et al., 2014; Saleh et al., 2020). It is also possible that reduction of porosity around the CNS via the rapid growth of concretion matrix further delayed its decay until after the neural tissue was robustly molded (McCoy et al., 2015a, 2015b). The present Carboniferous example validates earlier observations of euarthropod CNS tissues preserved through a fundamentally different taphonomic pathway (see Table S1).This proposed taphonomic pathway also explains the presence of kaolinite along the exoskeletal articulations between the prosoma and opisthosoma as well as between the opisthosoma and telson (Fig. 1A; Figs. S1A and S1B). In life, these articulation sites would have contained arthrodial membrane, which is markedly softer than the carapace. Such material may have also been molded by siderite and subsequently decayed, leaving voids that were partially filled by the growth of kaolinite.The presence of kaolinite in the examined CNS was not essential to its fossilization but was critical to its recognition because of its contrasting color compared to the remainder of the fossil and its host concretion. This record suggests that other examples of molded neural tissue could be preserved in Mazon Creek fossils. However, such evidence may be more cryptic and difficult to recognize, represented only by slight topographic variation in the siderite matrix in the absence of substantial mineral infillings. Hence, future studies on the Mazon Creek Konservat-Lagerstätte should consider careful exploration of the subtle topographic features on fossil surfaces that may assist in the possible detection of exceptionally preserved labile tissues.This research was supported by funding from an Australian Research Council Discovery Project grant (DP200102005 to J. Paterson and G. Edgecombe), a University of New England Postdoctoral Research Fellowship (to R. Bicknell), and a Charles Schuchert and Carl O. Dunbar Grants-in-Aid award (to R. Bicknell). R. Gaines also acknowledges support from G.G. Starr. We thank Susan Butts (Yale Peabody Museum) for facilitating access to the examined specimen, Malcolm Lambert for aid with EDS, and Steffen Harzsch for the image of a Limulus polyphemus CNS. Finally, we thank the four anonymous reviewers for their insightful comments that greatly improved the manuscript. Open access to this work is supported by a grant from the Wetmore Colles Fund (Harvard University, Museum of Comparative Zoology).

中文翻译：

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310 岁马蹄蟹的中枢神经系统：扩大神经系统保存的埋藏窗口

中枢神经系统 (CNS) 提供了对现存和灭绝动物群体行为和生态的独特见解。然而，神经组织脆弱且容易快速腐烂，因此它们作为化石的出现主要局限于寒武纪伯吉斯页岩型沉积物和新生代琥珀包裹体。我们描述了来自美国伊利诺伊州石炭纪晚期（莫斯科）Mazon Creek Konservat-Lagerstätte 的鲎 Euproops danae 中保存完好的 CNS。E. danae CNS 表明，马蹄蟹的一般前体合成神经节组织在超过 300 年的时间里基本上保持不变，尽管当时形态和生态多样化。此外，它揭示了真节肢动物 CNS 可以通过在菱铁矿中成型来保存，并表明在马松溪动物群中可能存在更多的例子。这一发现填补了真节肢动物中枢神经系统化石记录的重大时间空白，并扩大了保存古生代详细古神经解剖学数据的埋藏范围到边缘海洋沉积物的菱铁矿结核 Lagerstätten。中枢神经系统 (CNS) 在动物中起着关键作用功能、行为和生态学，并包含为复杂生物进化提供信息的有价值的形态学数据（Schmidt-Rhaesa 等，2015）。尽管中枢神经系统富含脂质的成分使其易于快速腐烂（Sansom，2016），最近的研究表明，神经组织可以作为寒武纪动物大型化石的碳质压缩物保存在开放海洋沉积物中（Edgecombe 等人，2015 年；Strausfeld 等人，2016 年；Ortega-Hernández 等人，2019 年；补充文件中的表 S1材料 1)。在新生代琥珀之前的年轻沉积物中，古神经解剖学遗骸极为罕见，这在我们对中枢神经系统进化的理解中留下了深刻的空白。值得注意的例外包括为石炭纪 Tullimonstrum gregariumRichardson，1966 年（McCoy 等人，2016 年）描述的推定大脑和三叠纪昆虫中的磷酸化腹侧神经索（Montagna 等人，2017 年），这表明可以通过 Tapho 捕获古神经解剖学结构古生代伯吉斯页岩型保存以外的其他途径（巴特菲尔德，1995 年；盖恩斯，2014 年），尽管极其罕见。我们在美国伊利诺伊州宾夕法尼亚州（莫斯科）Mazon Creek Konservat-Lagerstätte 的 belinurid Euproops danae（Meek 和 Worthen，1865 年）中描述了一种保存异常完好的 CNS。在 E. danae 中发现古神经解剖学意义重大，因为 xiphosurids（马蹄蟹）是现存的唯一完全水生的真螯足目，它们的化石记录对于重建真节肢动物的复杂进化史至关重要（Lamsdell，2016）。Euproops danae 与现存的 Limulus polyphemus (Linnaeus, 1758) (Haug and Rötzer, 2018) 具有相似的前体附属物组织，并且是 Mazon Creek (Raymond, 1945) 和全球 (Haug and Rötzer, 2018 年；比克内尔和佩茨，2020 年）。因此，这些关于 E 的新数据。danae 告知了这个主要真足类动物的内部解剖结构，代表了化石马蹄蟹中第一次中枢神经系统保存的发生，并为化石神经组织的保存模式提供了新的线索。我们回顾了耶鲁皮博迪博物馆（新Haven, Connecticut, USA) 古无脊椎动物学部 (YMP IP)。一个标本 (YPM IP 168040) 显示出保留的内部解剖结构的证据。该样品是在普通 LED 灯下使用配备佳能 MP-E 65 毫米微距镜头（完整样品）和佳能 MP-E 65 毫米 1×–5× 的佳能 EOS 5DS 数码单反相机拍摄的一系列堆叠图像微距镜头（CNS 特写）和 Cognisys StackShot 3X 堆叠系统。照片使用 Helicon Focus 7 (https://www.heliconsoft. com/heliconsoft-products/helicon-focus/)。使用 JEOL JSM-6010LA 扫描电子显微镜 (SEM) 在低真空和 20 kV 电压下进行背向散射和能量色散 X 射线光谱 (EDS) 分析以检查 CNS 的组成。标本没有涂层。标本 YPM IP 168040 包含 E. danae 内部解剖结构的第一个已知记录，其部分和对应物的方面均保留（图 1；补充材料中的图 S1）。该标本从背面看是一个完全铰接的个体，在菱铁矿结核中保留了有限的浮雕，这是典型的马松溪化石（克莱门茨等人，2019）。前体长 6.9 毫米，宽 16.8 毫米，后体长 7.3 毫米，宽 11.2 毫米，尾骨长 7.9 毫米。根据视染色体大小，该标本可能代表了 Euproops 的第三个发展阶段（sensuHaug 和 Rötzer，2018 年）。前体的轴向区域具有双侧对称的复杂结构，带有白色（图 1A、1B 和 1G）。元素映射表明该特征富含铝和硅（Clements 等人，2019 年；图 1I 和 1J），而相对于菱铁矿基体而言，铁、钾和镁贫乏（图 1H、1M 和 1N） . 内部结构的形态由沿矢状轴定向的梭形环组成，具有七个成对且规则间隔的叶状横向延伸，通常向后长度增加（图 1B 和 1D）。虽然结构的最前三分之一被破坏并横向移位，两侧的横向延伸与限定环边界的铝硅酸盐的宽度之间存在直接连续性。在 prosoma-opisthosoma 和 opisthosoma-telson 关节处也观察到白色着色。 YPM IP 168040 标本中保存的内部结构在形态学上与 L. polyphemus 早期幼体和更成熟个体的 CNS 相当，特别是由融合形成的突节前体中的节段性神经节（Harzsch 等，2005；Göpel 和 Wirkner，2015；图 1E）。七对横向延伸对应于原大脑（视神经）、半大脑（螯肢）、四个步行腿和推腿的节段神经。梭形环状结构的开口代表食管孔（图 1B 和 1D）。没有证据表明标本 YPM IP 168040 中存在保留的牙体中枢神经系统。 内部轴向结构作为肠道的另一种解释被低估，因为对应于食道孔的显眼开口是真节肢动物消化道中没有类似物的特征，和L. polyphemus 肠道缺乏同色异谱组织（Zacaï 等人，2016 年）。 Euproops danae 为已灭绝的真足类的 CNS 提供了宝贵的见解。E. danae 和 L. polyphemus 的合节之间的对应关系表明现代和已灭绝的 xiphosurids 之间的功能和行为相似，尽管它们各自的进化枝之间存在巨大的时间和系统发育差距（Bicknell 和 Pates，2020）。该化石表明，剑鞘类中枢神经系统的基本组织在超过 300 年的时间里基本上保持不变。此外，L. polyphemus、E. danae 和大附肢茎群螯合物的中枢神经系统组织之间的解剖学相似（Tanaka et al. , 2013; Ortega-Hernández et al., 2019) 表明自寒武纪以来，euchelicerates 一直保持着这种保守的神经解剖结构。这个独特的 E. danae 标本代表了最早的明确证据，证明了来自微咸边缘海洋沉积物的真节肢动物神经解剖结构（Clements 等人., 2019)。元素映射表明 CNS——在可见光下呈白色（图 1G）——富含铝、硅和氧（图 1I-1K）。此外，SEM 成像显示，蠕虫状的板状、微米级微晶堆叠构成了白色材料（图 1F）。这些观察结果，再加上相对于基质的钾和镁的消耗，表明突出中枢神经系统的白色矿物是高岭石。高岭石在 Mazon Creek 化石中有很好的记录（Baird 等人，1986 年；Cotroneo 等人，2016 年；Clements 等人等，2019）。它通常作为一种空隙填充矿物出现，沉淀在结核腔内。这包括骨骼溶解的化石内部空隙，植物茎被碳化并经历体积损失，留下空间，以及文石双壳贝壳溶解在结核基质中（Baird 等人，1986 年；Cotroneo 等人，2016 年；Clements 等人等，2019）。在 Mazon Creek 材料中，高岭石偶尔与闪锌矿和方铅矿伴生，表明埋藏期间的后期矿化（Keller，1988），更常见的是与黄铁矿，可能形成于早期成岩作用或后期成矿作用。基于其发生的这些方面，马宗溪化石中的高岭石一直被解释为起源于晚期成岩（Baird 等，1986，1997；Clements 等，2019），在化石完成后很久才在空隙中沉淀。检查的 CNS 中高岭石微晶的形态（图 1F）证实了后期沉淀物的起源，与先前的解释一致。然而，高岭石并不是捕获古神经解剖学信息的原始化石化过程的组成部分。取而代之的是，高岭石沉淀在神经组织腐烂后长期存在的空隙中。因此，中枢神经系统最初是作为模具保存的，在分解过程中失去结构完整性之前，矿物质在高度不稳定的组织周围生长时被捕获。元素分布图（图 1H-1N；图 S2）显示，CNS 外缘很尖锐，基体由菱铁矿组成，如铁、碳和氧的富集所示（图 1H 和 1K；图 S2） ）。中枢神经系统周围的菱铁矿与包裹标本的结核基质具有相同的成分和质地。检查中枢神经系统的保存要求菱铁矿在分解生物体周围快速生长，在三个维度上塑造中枢神经系统。然后中枢神经系统衰变，在其外部模具内留下空隙，由菱铁矿矿物基质稳定。这个空隙随后被高岭石的沉淀填充（图 2）。这种途径有两个重要意义。(1) 菱铁矿矩阵必须非常快地就位以捕获神经组织。虽然这种快速增长可能难以解释（例如，Berner，1968 年；Yoshida 等人，2020 年），但它目前是 Mazon Creek Konservat-Lagerstätte 内被接受的特殊保护模式（Clements 等人，2019 年）。这种保存途径被认为产生了在 Mazon Creek 结核中观察到的扁平复合模具，特别是真皮、表皮和其他外部结构（Baird 等人，1986 年；Clements 等人，2019 年）。然而，这种途径也可以保存更不稳定的内部组织，例如观察到的 CNS，这在 Mazon Creek 化石中非常罕见。固结基质的快速沉淀与从含化石的固结物中报告的 δ13C 值的显着窄范围一致（Cotroneo 等人，2016 年）。在长时间的结核生长过程中，由于氧化剂耗尽和主要细菌代谢途径的转换而导致的孔隙水生物地球化学变化通常会导致从中心到边缘的结核碳同位素值发生显着变化（Raiswell 和 Fisher，2000 年）。尽管类似地抑制 δ13C 变化可能是由于持续的普遍生长，而不是快速同心生长（Mozley 和 Burns，1993），但菱铁矿中 CNS 的稳健成型表明，快速普遍的结核增长更有可能（Sellés-Martínez，1996） . 因此，在 Mazon Creek 结核中观察到的有限范围的同位素变化值得注意（Cotroneo 等人，2016 年），并支持腐烂生物体周围的菱铁矿快速发育。（2）通过成型保存 CNS 意味着在前体盾下其他软组织的损失到中枢神经衰弱。在现代 xiphosurids 中，CNS 被厚厚的血管膜包裹着 (Göpel and Wirkner, 2015)。E. danae 中的这种膜可能减缓了合成神经节的衰变（相对于其他内部结构）并促进了这些脆弱组织的快速成型。鉴于导致菱铁矿沉淀的含铁孔隙水条件，溶解的 Fe2+ 也可能在延迟神经组织衰变方面发挥了作用（Schweitzer 等人，2014 年；Saleh 等人，2020 年）。也有可能通过凝结物基质的快速增长来减少 CNS 周围的孔隙率，从而进一步延迟其衰变，直到神经组织牢固成型后（McCoy 等人，2015a，2015b）。本石炭纪的例子证实了早期观察到的真节肢动物 CNS 组织通过根本不同的埋藏途径保存（见表 S1）。这个提议的埋藏途径还解释了沿着前体和后体之间以及后体和后体之间的外骨骼关节存在高岭石的原因。 telson（图 1A；图 S1A 和 S1B）。在生活中，这些关节部位会包含关节膜，其明显比甲壳软。这种材料也可能由菱铁矿铸模而成，随后腐烂，留下被高岭石生长部分填充的空隙。所检查的 CNS 中高岭石的存在对其化石化并不重要，但对其识别至关重要，因为与化石的其余部分及其寄主结核相比，高岭石的颜色对比鲜明。这一记录表明，其他模制神经组织的例子可以保存在 Mazon Creek 化石中。然而，这些证据可能更加隐秘且难以识别，仅表现为在缺乏大量矿物填充物的情况下菱铁矿基质的轻微地形变化。因此，未来对 Mazon Creek Konservat-Lagerstätte 的研究应该考虑仔细探索化石表面的细微地形特征，这可能有助于发现保存完好的不稳定组织。这项研究得到了澳大利亚研究委员会发现项目赠款（DP200102005 授予 J. Paterson 和 G. Edgecombe）、新英格兰大学博士后研究奖学金（授予 R. Bicknell）以及 Charles Schuchert 和 Carl O. Dunbar 的资助助学金奖（授予 R. Bicknell）。R. Gaines 也感谢 GG Starr 的支持。我们感谢 Susan Butts（耶鲁皮博迪博物馆）为获得检查标本提供便利，感谢 Malcolm Lambert 提供 EDS 帮助，以及 Steffen Harzsch 提供 Limulus polyphemus CNS 图像。最后，我们感谢四位匿名审稿人的深刻见解，大大改进了手稿。这项工作的开放获取得到了 Wetmore Colles 基金（哈佛大学，比较动物学博物馆）的资助。