河北唐山西域山晚寒武世长山组的树形笔石

DENDROID GRAPTOLITES FROM CHANGSHAN FORMATION (LATE CAMBRIAN) OF XIYUSHAN MOUNTAIN, TANGSHAN, HEBEI

唐山地区奥陶纪树形笔石早有报道(孙云铸,1935),但本文记述的,在本区西域山长山组中部所发现的寒武纪笔石尚属首次。这是一个古老的,以固着底栖为生的原始树形笔石动物群,包括了Dictyonema, Airograptus和Dendrograptus 3属、6种(其中1新种)。证明了Airograptus属的地质历程最早可追溯到中长山期。也揭示了本区繁荣的奥陶纪树形笔石群从上寒武统的属种演化过渡而来的。

The Cambrian and Ordovician Strata are well-developed in the Tangshan area, Hebei province, with rich trilobites, graptolites, cephalopods, etc. A new dendroid graptolite fauna was discovered for the first time by the writer and his colleagues from the dark bluish grey argillaceous shale of the Changshan Formation (Late Cambrian)in the Xiyushan Mountain, Zhaogezhuang, Tangshan. This graptolite fauna formerly was only known from Xiaoxian, N. Anhui and Tai'an, Central-South. Shandong in China. The new materials described in this paper consist of 3 genera and 6 species (including one new species and 3 unidentified species) which are listed as follows: Dictyonema sp., Airograptus sp., Den- drograptus lonchoformis Lin, Dendrograptus pronus Lin, Dendrograptus ypsiliformis sp. nov., and Dendrograptus? sp. As mentioned above, the dendroid graptolites characterized by benthic, endemic and oriental forms are one of the earliest graptolite groups in the North China Region. Among them, the Dictyonema sp. found from the Changshan Formation of Xiaoxian, N. Anhui probably represents benthic forms; Dendrograptus lonchoformis Lin and Dendrograptus pronus Lin are known to occur in the Fengshan Formation of N. Anhui, W. Hebei and Central-South Shandong. Dendrograptus ypsiliformis sp. nov. is a small (4—5 mm in length) and primitive form, representing a new species of the genus Dendrograptus. The speciments of Dendrograptus? sp. closely resemble Dendrotubus in some characters and shape of stipes, but differs from the later in the peculiar character and arrangment of the thecae (autothecae). Since the specimens are too few and fragmentary to make a definite determination, it is preferable to put a question mark after the generic name. In the shape and character of the thecae (e.g., the furcate or peltate apertural process, etc.), our specimens of Airograptus sp. indicate that it is the most primitive and oldest species. This genus was established in 1916 by Ruedemann from the Ordovician forms. In China, the representatives of this genus were described by Mu (1953, 1955) from the upper part of the Yehli Formation and by Lin (1980, 1987) from the Late Cambrian Fengshan Formation. Recently, the writer is of the opinion that this genus ranged from Changshanian of middle Late Cambrian to Early Ordovician. The Changshanian airograptid forms were the Airograptus-like ancestors. Some bottom-living forms in the Cambrian Sea are revealed by the Presence of a thickened stem with a disc of attachment as in Dendrograptus lonchoformis, D. ypsiliformis sp. nov. Airograptus sp. etc, or by a plane disc in the proximal part of the rhabdosome as in Dendrograptus pronus, etc. In addition, the new dendroid graptolites as mentioned above and the associated shelly fauna might have lived in shallow water, probably providing the evidence of an euphotic zone environment.