SGER: A Novel Dinosaurian Tissue Exhibiting Unusual Preservation

落基山脉博物馆2003年夏季野外发现了一只充满惊喜的霸王龙。这种恐龙在股骨内表面拥有一种新的组织类型，具有潜在的生理和系统发育意义。它在结构上不同于其他化石骨骼类型，可能是鸟类髓质骨的功能类似物，髓质骨是一种特殊的骨骼类型，用于短期储存用于蛋壳形成的钙储备。这种短暂的骨组织不是由现存的爬行动物或哺乳动物产生的，而是由排卵期的雌鸟产生的雌激素水平增加而形成的。如果随后的分析证实这种新组织类似于鸟类的髓质骨，这将是确定恐龙性别的第一个客观手段，并提供有关动物生殖阶段的额外信息。关于这种新组织起源的假设将通过对样本进行各种化学、显微镜和分子分析来检验，因为鸟类髓质骨组织在结构和化学上都不同于现存鸟类的其他骨骼类型。例如，与其他骨类型相比，现有髓质骨的酸性粘多糖和硫酸氨基葡萄糖聚糖浓度增加，并且对高二胺铁（HID）染色有明显的反应。然而，这种新组织的存在并不是在这个恐龙标本中观察到的唯一惊喜。在骨脱矿后，发现了完全出乎意料的特征，并且从未报道过这个年龄的骨组织。新组织的脱矿基质具有弹性和弹性，并且具有多次脱水和再水合的能力而不失去这一特性。皮质骨的脱矿也显示基质呈纤维状且高度定向，与现存骨中的脱矿胶原一致。此外，在完全脱矿后，皮质骨内显示出柔韧的分支血管，与脱矿和胶原酶消化后从现有骨中恢复的血管没有区别。恐龙血管的微观结构与处理过的鸵鸟骨血管中保留的红细胞一致，这些微观结构的内部内容物让人想起有核红细胞。最后，皮质骨的脱矿释放出具有类似于柄足的外部突起的微结构，这些微结构与现存鸟类皮质骨脱矿后观察到的骨细胞几乎相同。这些微观结构也具有内部内容物。该项目将对这些特殊组织进行化学、分子和微观结构分析。这些恐龙组织在分子成岩作用、组织/分子保存和石化过程等先前未被怀疑的方面具有巨大的潜力，更不用说独立测试现有的系统发育假说和进化的潜力。这个项目的风险超过了潜力的平衡，因此似乎完全符合SGER基金的意图。

ABSTRACTThe Museum of the Rockies 2003 summer field season yielded a Tyrannosaurus rex that is full of surprises. This dinosaur possesses a novel tissue type on the internal (endosteal) surface of the femur that has potential physiological and phylogenetic significance. It is structurally distinct from other fossil bone types, and may be the functional analogue of avian medullary bone, a specialized bone type that serves as short term storage for calcium reserves used in the formation of eggshells. This ephemeral bone tissue is not produced by extant reptiles or mammals, but forms in response to increased estrogen levels produced by ovulating female birds. If subsequent analyses confirm that this novel tissue is analogous to avian medullary bone, it will be the first objective means of assigning gender to a dinosaur, and provides additional information regarding the reproductive phase of the animal.The hypothesis regarding the origin of this new tissue will be tested by subjecting samples to various chemical, microscopic and molecular analyses, as avian medullary bone tissue is distinct from other bone types in living birds both structurally and chemically. For example, extant medullary bone has increased concentrations of acid mucopolysaccharides and sulfated glucosaminoglycans over other bone types, and responds in a distinct manner to high iron diamide (HID) staining.However, the presence of this novel tissue is not the only surprise observed in this dinosaur specimen. Upon demineralization of the bone, characteristics were revealed that were utterly unexpected, and again, never reported for bone tissues of this age. The demineralized matrix of the new tissue was elastic and stretchy, and had the capacity to be dehydrated and rehydrated many times without losing this characteristic. Demineralization of cortical bone also revealed the matrix to be fibrous and highly oriented, consistent with demineralized collagen in extant bone. Additionally, upon complete demineralization, pliable branching vessels were revealed within the cortical bone that are indistinguishable from those similarly recovered from extant bone after demineralization and collagenase digestion. The dinosaur vessels possessed microstructures consistent with red blood cells retained in treated vessels from ostrich bone, and these microstructures contained internal contents reminiscent of nucleated red blood cells. Finally, demineralization of the cortical bone liberated microstructures possessing external projections similar to filipodia, which are virtually identical to osteocytes observed after demineralization of cortical bone from extant birds. These microstructures also possess internal contents.This project will pursue chemical, molecular and microstructural analyses of these exceptional tissues. These dinosaur tissues have great potential to elucidate previously unsuspected aspects of molecular diagenesis, tissue/molecular preservation and processes of fossilization, not to mention the potential to independently test existing phylogenetic hypotheses and evolution. The risk of this project is more than balanced by the potential, and therefore seems to fall well within the intent of SGER funds.