Organic phase (extracellular matrix, osteocyte, blood vessel) preservation in dinosaur bone: Chemical composition and hypotheses of preservation

骨作为一种硬组织，具有很好的可塑性，为脊椎动物的进化提供了极其丰富的化石记录。骨是70体积%的无机相（IP）和30体积%的有机相（OP）的复合材料。人们早就认识到，除了它们的形状外，化石骨骼还保留了它们的组织结构。在光学显微镜下观察，骨基质不受结晶化的影响，因为微晶模式没有改变成岩作用。因此，骨矿化过程中的主要变化必须发生在纳米结构水平上。最近，人们已经认识到，通过用弱有机酸仔细消化矿化良好的恐龙化石骨，可以释放骨中的OP，如骨细胞残余物、血管，有时还可以释放细胞外基质和软骨。OP释放的发现导致了关于这些柔韧的有机残留物作为原始软组织保存与骨降解细菌产生的生物膜的性质的争议。虽然现在的证据支持原始软组织，但内源性OP保存需要独立的确认，因为它对脊椎动物化石记录具有重要意义。二十年的收购形成了申请人桑德实验室中世界上最广泛的骨骼化石组织学样本收藏的基础。虽然大多数样本保存完好，但另一组样本对本项目特别重要。这些样品显示出复杂和不寻常的成岩历史，通常导致组织学保存不佳。这些标本在整个样品库中随机出现，与地质年代和沉积环境无关。我们的建议是DFG研究单位第一个资助期项目A2的更新，用于2685“化石化”。因此，拟议项目的总体目标保持不变，即：来理解骨骼的骨化。因此，第二个供资期的目标是由第一个供资期的四个主要成果推动的：1. OP保存是化石矿化骨的标准特征。2. OP保存与样品的地质年龄无关。3. OP保存与样品的沉积环境无关。4.从化石过矿化骨中释放的OP可能是内源性的。在第二个资助期，我们特别想解决三个新的假设：H1：强烈的成岩蚀变破坏OP。H2：强烈的成岩蚀变揭示了骨矿化的物理化学边界条件。H3：血红素在骨骼化石中保存得很久。为了解决这些假设以及早期的假设，我们将使用最先进的分析方法，从有机化学（OP和血红素）和矿物学（IP和成岩阶段，特别是在保存较差的样品）。

Bone as a hard tissue fossilizes well, providing the exceedingly rich fossil record of vertebrate evolution. Bone is a composite material of an inorganic phase (IP) of 70% by volume and an organic phase (OP) of 30% by volume. It has long been recognized that in addition to their shape, fossil bones also preserve their histological structure. Seen in a light microscope, the bone matrix is not affected much by fossilization because crystallite patterns are not altered diagenetically. The major changes during fossilization thus must take place at the nanostructural level.Recently it has been recognized that OP in bone such as osteocyte remains, blood vessels and sometimes extracellular matrix and cartilage can be liberated from well-mineralized fossil dinosaur bone by careful digestion with weak organic acids. The discovery of OP liberation led to a controversy over the nature of these pliable organic remains as original soft tissue preservation vs. biofilms produced by bone-degrading bacteria. Although the evidence now is in favor of original soft tissue, endogenous OP preservation requires independent confirmation because of its significance for the vertebrate fossil record. Two decades of acquisition form the basis of one of the world’s most extensive collections of histological samples of fossil bone in applicant Sander’s lab. Whereas most samples are well preserved, another set of samples is of particular interest for this project, however. These are samples that show a complex and unusual diagenetic history, often resulting in poor preservation of the histology. These specimens occur randomly throughout the sample base, independent of geologic age and sedimentary environment.Our proposal is a renewal of project A2 of the first funding period of the DFG research unit FOR 2685 “Fossilization”. Thus, the overarching aim of the proposed project remains the same, i.e., to understand the fossilization of bone. The aims for the second funding period are thus motivated by the four major results of the first funding period: 1. OP preservation is a standard feature of fossil permineralized bone. 2. OP preservation is independent of the geologic age of the sample. 3. OP preservation is independent of the depositional environment of the sample. 4. OP liberated from fossil permineralized bone is likely endogenous. In the second funding period, we particularly want to address three new hypotheses: H1: Strong diagenetic alteration destroys OP. H2: Strong diagenetic alteration reveals physicochemical boundary conditions of bone mineralization. H3: Heme is preserved in deep time in fossil bone. To address these hypotheses as well as the earlier ones, we will use state-of-the-art analytical methods from organic chemistry (for the OP and heme) and mineralogy (for the IP and diagenetic phases, especially in the poorly preserved samples).