论中国早寒武世原牙形类和牙形状化石——分类评述和地层意义

原牙形类和牙形状化石是早寒武世微小骨骼化石中非常特征的一个类群。自二十世纪70年代以来,这些齿状的微型磷质骨片化石在中国下寒武统含小壳化石地层中被大量发现,据统计已描述有25属52种。通过文中的评述和讨论,证实其中的一些属种是次异名或属于无效的分类名称,还有一些在归属上尚存在疑问。通过对原牙形类和牙形状化石定义的讨论,将先前指定为原牙形类的13个属进行了分类评述。表明其中的5个属是次异名,还有2个属是未知的节肢动物。其它的12个牙形状化石属中也有5个属是次异名,它们不仅显示了有多种动物亲缘的牙形状形态,而且大多属于绝灭生物,只有Beshtashella和Paraformitchella(=Beshtashella)被指定为软体动物。文中还简要地讨论了大多数属的时空分布,包括3个阶段的原牙形类地层分布,这不仅具有划分对比地层的意义,而且还反映了原牙形类的演化趋势。

EARLY CAMBRIAN PROTOCONODONTS AND CONODONT-LIKE FOSSILS FROM CHINA: TAXONOMIC REVISIONS AND STRATIGRAPHIC IMPLICATIONS

Protoconodonts and conodont-like microfossils are characteristic components in the early Cambrian skeletal faunas.Since the 1970 s,these tooth-like phosphatic sclerite fossils have been widely recovered from the Lower Cambrian of China,and altogether 25 genera and 52 species of protoconodonts and conodont-like fossils have been described,although some taxa represent synonyms or invalid taxonomic names,and some assignments are apparently inappropriate.Through a brief review and discussion,the distinction between protoconodonts and conodont-like fossils is denoted here.There are 13 genera previously assigned to protoconodonts in the literature,but present taxonomic revisions show that 5 of them are junior synonyms of other taxa,and 2 represent unknown arthropods.The other 12 genera,of which 5 are also junior synonyms,only reveal a conodont-like morphology with various zoological affinities:most of them are enigmatic,and only Beshtashella and Parafomitchella(=Beshtashella)may be assigned to mollusks.The spatial and temporal distribution of the most genera is briefly discussed.Three intervals of stratigraphic ranges for the protoconodonts not only have significant implications for stratigraphic correlations but also may reflect their evolutionary trend.