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Journal of Paleontology
protaspid stage of both I. ichangensis and E. sinensis is always <0.45mm (Zhang and Pratt, 1999). Late protaspid stages of I. ichangensis and E. sinensis fromHenan are 0.42–0.52mmwide. The earliest known stage of E. sinensis from Hubei (South China plate), which is morphologically comparable to the late protaspid stage of the same species from Henan, is slightly larger, with a width varying between 0.53 and 0.64mm (Dai and Zhang, 2012). The size comparison shows that the protaspides in
Ellipsocephalidae tend to be larger than their equivalents in Estaingiidae. Laibl et al. (2017) showed that protaspid size may be related to taxonomy and, more significantly, to paleogeogra- phy. The variability in size between protaspides of Ellipsocepha- lidae and Estaingiidae can thus be either the result of taxonomic differences, or specific differences in paleogeographic settings. Since Baltica was located at higher latitudes than South China during Cambrian Epoch 2 (e.g., Torsvik and Cocks, 2013), it seems reasonable to assume the differences can be related to the different environmental settings of these continents. Laibl et al. (2017), nonetheless, reported extremely small protaspides from Baltica. This may be a result of the small sample size fromBaltica (only five trilobite species in Laibl et al., 2017) and/or taxonomic bias because the studied samples from Baltica contained protaspides of Eodiscida and Olenida only. The size variability between late protaspides of E. sinensis
from Henan and Hubei (assuming they are conspecific) may be a result of preservation and taphonomy (phosphatized in Henan versus internal molds in Hubei; see Zhang and Pratt, 1999; Dai and Zhang, 2012) or environmental differences (micritic lime- stones in Henan versus black shales in Hubei). The variability in size of the earliest trilobite stages may also be a result of these factors. The number of species compared here is, however, insufficient to suggest some more general conclusions.
Acknowledgments
This manuscript benefited from constructive reviews by J.O.R. Ebbestad and P. Jell. We thank B. Hunda and N.C. Hughes for their editorial help with the manuscript. We are grateful to S. Pates for his English proofreading. L. Laibl was financially supported byMinistry of Culture of the Czech Republic (DKRVO 2017/06, National Museum, 00023272) and by Research Plan RVO 67985831 of the Institute of Geology of the CAS. Magn. Bergvalls Stiftelse (MBS) has supported research by P. Ahlberg.
Accessibility of supplementary material
Data available from the Dryad Digital Repository: https://doi. org/10.5061/dryad.36n6p34
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