珊瑚形钙质疑问生物Amsassia新材料及其绿藻类归属新证

NEW MATERIAL OF CORALOMORPH PROBLEMATICAL CALCAREOUS FOSSILS AMSASSIA,AND NOVEL PROOF FOR ITS CHLOROPHYTES ATTRIBUTION

Amsassia是一类仅存在于奥陶纪的珊瑚形钙质疑问生物,长期被认为是一种原始的床板珊瑚,近年来通过对其形态结构,分裂方式等方面的研究,已基本排除了它与珊瑚、海绵等类群的亲缘关系,认为它可能是一种钙化藻类化石,与现生绿藻类刚毛藻属Cladophora有些相似,但其具体的系统古生物分类位置还尚无定论。本文报道了产自于中国新疆塔里木盆地上奥陶统良里塔格组礁灰岩中的新种Amsassia talimuensis sp.nov.。在A.talimuensis中观察到了二至多分裂的现象,三种不同状态下的似横板结构,同时还发现了与现生Cladophora丝体末端细胞形态相似的个体。此外,这个新种显示A.talimuensis的分裂通常发生于收缩的似横板结构之下,这一特征与现生Cladophora的节下分枝类似。同时,XRF(X射线荧光光谱分析)扫描分析发现A.talimuensis体壁周围存在金属元素特异性聚集的现象,与现生Cladophora在细胞壁周围沉淀重金属离子的生理特征可以对应。因此,Amsassia talimuensis sp.nov.的发现为Amsassia很可能是一类与现生Cladophora亲缘关系较近的钙质绿藻提供了强有力的新证据。

Amsassia are modular coral-like calcareous fossils with uncertain affinity and only existed in the Ordovician Period.They were initially identified as a kind of primitive tabulate coral.In recent years,through the study of their morphology,structure,module increase and other features,their biological affinity with coral,cyanobacteria,sponges and other groups has been basically ruled out,and it is presumably to be a kind of calcified algal fossil similar to the extant green algae,Cladophora.However,the confirmed systematic position of Amsassia has not been confirmed yet.This study reports a new species,Amsassia talimuensis sp.nov.,from the reef limestone of the Upper Ordovician Lianglitage formation in the Tarim basin,Xinjiang,China.In these samples,the phenomenons of longitudinal bipartite fission to polypartite fission,the tabulae-like structures in three different states,and modules with similar morphology to the terminal cells of the filament of the extant Cladophora are observable.This new species shows that the longitudinal fission of A.talimuensis usually takes place under the tabulae-like structures,which is similar to the infranodal branching of Cladophora.At the same time,XRF scanning analysis found that there is an obvious enrichment of metal elements around the modular wall of A.talimuensis.Therefore,the discovery of A.talimuensis provides important new evidence that Amsassia is probably a kind of calcareous green algae closely related to the extant green algae,Cladophora.