Serrated microstructures on carapaces of Eosestheria (Branchiopoda: Diplostraca) in the Early Cretaceous Jehol Biota and discussion on the taxonomic value of these structures

Serrated microstructures on the growth lines of some fossil conchostracans have been previously regarded as a key characteristic for judging the family Afrograptidae. Consequently, more than 20 relatively diverse genera were assigned into Afrograptidae based on the presence of serrated structures. This has created a series of taxonomic disputes in regard to fossil conchostracans. In this study, serrated microstructures on the growth lines of two species, namely, Eosestheria ovata and E. middendorfii, in the Early Cretaceous Jehol Biota are reported and described in detail. Our microstructural study shows that these structures are pit-shaped and are actually insertion remains of setae. Such microstructures commonly exist on the growth lines of some extant spinicaudatans. The setae probably served a sensory function. The presence or absence of these setae in extant species of the same genus can be variable and size of the setae of the same species can also be variable. Thus they are not appropriate to be considered as possessing important taxonomic value. Based on this conclusion, the species of the family Afrograptidae are listed in conjunction with the results of our previous study. (C) 2018 Elsevier Ltd. All rights reserved.