SGER: A Novel Dinosaurian Tissue Exhibiting Unusual Preservation

2003年落基山脉博物馆夏季野外活动期间，诞生了一只充满惊喜的暴龙霸王龙。这种恐龙在股骨内(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。它在结构上与其他化石骨类型不同，可能是鸟髓质骨的功能类似物，鸟髓质骨是一种特殊的骨类型，用作形成蛋壳所用的钙储备的短期储存。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，而是在雌性鸟类排卵时产生的雌激素水平增加的反应下形成的。如果随后的分析证实这种新的组织类似于鸟类的髓质骨，它将是第一个客观的鉴定恐龙性别的方法，并提供关于动物生殖阶段的额外信息。关于这种新组织的起源的假设将通过对样品进行各种化学、显微镜和分子分析来检验，因为鸟类的髓质骨组织在结构和化学上都与现存鸟类的其他骨骼类型不同。例如，现存的髓质骨比其他类型的骨增加了酸性粘多糖和硫酸氨基葡聚糖的浓度，并且对高铁二胺(HID)染色有明显的反应。然而，在这个恐龙标本中观察到的这种新组织的存在并不是唯一令人惊讶的。在骨骼脱矿后，发现了完全出乎意料的特征，而且同样，这个年龄段的骨组织从未报道过。新组织的脱钙基质具有弹性和延展性，可以多次脱水和再水化，而不会失去这一特性。皮质骨的脱矿也显示基质是纤维性的和高度定向的，与现存骨骼中脱矿的胶原相一致。此外，在完全脱矿后，皮质骨内可见柔韧的分支血管，这些血管与脱矿和胶原酶消化后从现存骨中恢复的类似血管难以区分。这些恐龙血管具有与处理后的鸵鸟骨血管中保留的红细胞一致的微结构，这些微结构含有让人想起有核红细胞的内部内容物。最后，皮质骨的脱矿释放了具有类似纤足的外部突起的微结构，这些微结构与从现存鸟类的皮质骨脱矿后观察到的骨细胞几乎相同。这些微观结构也有内在的内容。这个项目将对这些特殊的组织进行化学、分子和微观结构分析。这些恐龙组织具有巨大的潜力来阐明以前未被怀疑的分子成岩作用、组织/分子保存和石化过程，更不用说有可能独立测试现有的系统发育假说和进化。这个项目的风险超过了潜在的平衡，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.