Early Cambrian protoconodonts and conodont-like fossils from China:Taxonomic revisions and stratigraphic implications

摘要

Protoconodonts and conodont-like microfossils are characteristic components in the early Cambrian skeletal faunas. Since the 1970s, 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 also are junior synonyms, only reveal a conodont-like morphology with various zoological affinities: most of them are enigmatic, and only Beshtashella and Parafomitchella (=Beshtashella) can be assigned to mollusks. The spatial and temporal distribution of the most genera is briefly discussed. Three intervals of stratigraphic distribution for the protoconodonts not only have significant implications for stratigraphic correlations but also may reflect their evolutionary trend.