140OΜα前的后生动物实体化石?

ARE THESE THE METAZOAN BODY FOSSILS FORMED BEFORE 1400 MA?

本文首次报道了在我国豫西晚前寒武系白草坪组中发现的一种可能的蠕虫状后生动物实体化石:Ruyangia Cylindrica Hu et Meng,1989。化石产于砂岩表面浪成波痕之波谷中,圆筒状,已压扁,中空,可见长度4.5～9.5cm,直径4mm左右,虫体外壁具体环,环背间距1.5～2mm,虫体一端较大,具平行纵向边缘的纵纹,可能为头部;另一端渐尖,可能为尾部。与该实体化石伴生的有大量遗迹化石。已知白草坪组的时代超过1400Ma,因此,该实体化石的发现对研究地球上后生动物起源与早期演化等具重要意义。

Some probable worm-like body fossils and a large number of metazoan trace fossils have been recently found from the Bai Caoping Formation of the Ruyang Group of the Precambrian Changcheng System at Rnyang County of the western Henan, China. The myrmekitic-body fossils are preserved in the troughs of wave ripples ( well symmetrical and peaked crest ) of the fine grain sandstones. In the troughs there still remain a few purple-red mudstones. According to the annulations, size and distribution, the authors believe that the trace fossils discovered on this outcrop would be directly related to the activities of the probable worm-like animals. In this iegion, the Bai Caoping Formation lies on the Yun Mengshan Formation and under the Bei Dajian Formation. Because the Yun Mengshan Formation is not concordant with the Xiong'er Group ( 1950-1650 Ma. ), the isotopic age of 1492 Ma. ( glauconite, K-Ar method ) has been obtained from the glauconitic sandstones of the Bei Dajian Formation. So, the Bai Caoping Formation should be sedimented before 1400 Ma. On the other hand, the researches on biostratigraphy, the sec-tions of the strata, and the rock associations all show that the Ruyang Group in the western Henan should correspond to the Gao Shanhe Group, which corresponds with the Changcheng System ( 1800-1400 Ma ) in the Jixian region of Hebei and in the Xiao Qinling areas. It is clear that it is consistent with the results above. To sum up, the age of the probable worm-like body fossils is longer than 1400 Ma. Therefore, this discovery is very important to the further understanding of the Precambrian evolution of life,especially to the origin and the early evolution of me-tazoan. It also confirms that there have been more complex metazoans on the Earth before 1400 Ma. Moreover, it will be of great theoretical significance for the division and comparison of the late Precambrian strata in the Northern China.