燕辽、热河生物群脊椎动物化石黑素体多样性及其它色素成分

Color pattern, is one of the most important phenotype of vertebrates, functioned as thermoregulation, camouflage, display and advertising, and related to both animal habitat ecology and physiology. Among extant vertebrates, the chromatophores in fishes, amphibians, lizards and snakes consist of melanophores, Iridophores and Leukophores, Xanthophores and Erythrophores, are mainly positioned in the dermis of the integuments, and contain the pigements including melanosomes, carotenoids, pteridines, crystals of purines. Among mammals and birds, the chromatophores which produce the pigments in the hair and feathers are mainly produced by the melanocyte in the epidermis, which form the color of hairs or feathers, sometimes with carotenoids and other rare pigments in feathers. Since 1990s, many vertebrate fossils with integuments and appendages have been found from the Late Jurassic Yanliao and the Early Cretaceous Jehol Biota, including lamprey, fishes, amphibians, lizards, feathered dinosaurs, ornithopod dinosaurs, birds and mammals. Although the color patterns of several feathered dinosaur and bird fossils have been reconstructed relying on the melanosomes and the melanosome morphology of some fossil amniotes has also been evaluated, but these are still unknown in the other vertebrate groups, the other pigments, such as carotenoids, pteridines, crystals of purines etc. are also not investigated. This project will broadly investigate the vertebrate fossils with integuments and its appendage using SEM, TEM, Raman spectrum and Tof-sims technologies, to reveal the morphological diversity of melanosomes, other pigments and the shift of pigmentary system from the dermal to the epidermal in the vertebrate phylogeny.

颜色，作为脊椎动物最重要的表型特征之一，具有保护色、体温调节、信息交流等重要功能。在现生脊椎动物中，鱼类、两栖类、蜥蜴和蛇的色素细胞由黑素细胞、黄色素或红色素细胞、虹色细胞构成，产生真黑素、胡萝卜素、蝶呤等色素, 主要分布在真皮层，仅黑素细胞少量分布在表皮层。 而哺乳类毛发和鸟类的羽毛的色素主要由表皮层黑素细胞产生的真黑素、褐黑素以及胡萝卜素等其它色素构成。我国晚侏罗世燕辽生物群、早白垩世热河生物群产出了无颌类、鱼类、两栖类、蜥蜴、恐龙及古鸟类等有皮肤及其衍生物印痕的化石，虽然部分带羽毛恐龙及古鸟类的颜色依据黑素体被复原以及部分羊膜类的黑素体被调查过，但其它类群的黑素体以及黑素体之外的其它色素尚没有研究。本项目计划采用扫描电镜、透射电镜、拉曼光谱分析、飞行时间二次离子质谱等手段，对燕辽、热河生物群的黑素体多样性、其它色素成分、关键类型皮肤结构进行研究，揭示脊椎动物色素系统的演化过程。

经过四年的研究，已经完成了无颌类化石一例、两栖类化石一例、蜥蜴化石两例、潜龙化石一例、鸟臀类恐龙一例（鹦鹉嘴龙）、哺乳动物化石的黑素体形态研究。建立整个脊椎动物群的黑素体多样性变化，追索在脊椎动物系统发育过程中黑素体多样性变化的意义，最新的发现是鸟类谱系的黑素体多样性起源晚于哺乳动物黑素体多样性的起源，二者遵循不同的多样化路径。.在蜥蜴化石、潜龙化石、反鸟类化石通过广泛的X射线荧光分析发现有规律的元素分布，代表色素的差异，反应了色彩花纹。通过对部分现生鸟类羽毛的X射线荧光分析，发现部分元素富集能够反应颜色的深浅。发现潜龙的表皮角质细胞，呈椭圆形，最长直径不超过10微米，部分角质细胞呈立体保存，角质细胞的膜破损处露出黑素体的印痕，角质层厚度约有12-14层。而现生的鲸鱼、鸟类的角质细胞通常呈多边形，直径约30微米左右。这种现象代表了对水生习性的适应。在鹦鹉嘴龙化石的后肢的皮肤印痕中发现胶原纤维和黑色素层有规律交替叠压分布现象，胶原纤维在皮肤中分布于真皮层中，这种结构可能代表构成颜色的元素从真皮层色素系统在恐龙演化过程中的新变化。在一件归属于渤海鸟科的标本中发现了羽毛中只依赖结构不依赖黑素体的特征，显示该反鸟没有发育羽小枝的皮层，代表最早的非彩虹色泽的结构色。.总体说来，经过四年的研究，使得我们对燕辽、热河生物群中脊椎动物黑素体的多样性、色素系统的演化、颜色复原的整体认识上升到了一个新的台阶。