Geochemical extraction of ceratopsian remains from ironstone

Ironstone surrounds many fossils and has a hardness that provides a significant challenge to fossil conservators globally. There are various forms of ironstone, with the carbonate forms of siderite and silicates most often containing vertebrate fossils and potentially preserved soft tissues. The ironstone itself is much harder than the fossils preserved within, leading to the mechanical preparation of the fossils––typically using pin vises or airscribes––being time-consuming and presenting the risk of damage. Existing chemical methods for softening ironstone to prepare the fossils have varied success and also pose a risk of damaging the fossil itself. Here we show that carbonic acid can soften ironstone without damaging permineralized bone or potentially preserved soft tissues. Carbonic acid treatments reduced the hardness of ironstone without causing any significant change in hardness, color, chemical composition, or weight to permineralized ceratopsian bones or a modern cervid bone that retained nonmineralized internal tissues. In addition, we found that solutions of sodium hydroxide and hydrogen peroxide were viable for softening ironstone to remove from the permineralized bone when preserved soft tissue recovery is not a priority. The treatments proposed in this study are important as they are applicable to a range of preparation scenarios, are cost-efficient, are relatively safe to handle, and cause no damage to permineralized fossil bones. Putting these methods into practice can lead to more efficient and safe preparation of fossils in ironstone.铁质岩（Ironstone）常包裹诸多化石，其硬度给全球古生物化石修复人员带来了极大挑战。该岩石存在多种类型，其中以菱铁矿（siderite）碳酸盐相及硅酸盐相最为常见，这类铁质岩常赋存脊椎动物化石，且有可能保存有软组织残骸。由于铁质岩本身硬度远高于其所包裹的化石，因此采用机械法修复此类化石（通常使用针式手钻（pin vise）或气动刻笔（airscribe））不仅耗时极长，还存在损伤化石的风险。现有用于软化铁质岩以开展化石修复的化学方法效果参差不齐，且同样存在损伤化石本体的风险。本研究证实，碳酸可实现铁质岩的软化，且不会损伤矿化骨骼（permineralized bone）或潜在保存的软组织残骸。经碳酸处理后，铁质岩的硬度显著降低，而角龙类（ceratopsian）矿化骨骼以及保留有非矿化内部组织的现代鹿科（cervid）骨骼的硬度、色泽、化学成分及重量均未发生显著变化。此外，本研究发现，当无需优先提取保存的软组织时，氢氧化钠与过氧化氢混合溶液可有效软化铁质岩，以便将其从矿化骨骼上剥离。本研究提出的修复方法具有重要应用价值，其适配多种修复场景、成本低廉、操作相对安全，且不会对矿化化石骨骼造成任何损伤。将上述方法投入实际应用，可大幅提升铁质岩包裹化石的修复效率与安全性。