Taxonomic Revision of the Cambrian Trilobite Redlichia (pteroredlichia) and Stratigraphic Significance

The genus Redlichia is an important guide fossil for the subdivision and correlation of Cambrian biostratigraphy. The FAD of Redlichia was once proposed to define the base of Cambrian Stage 4. However, the taxonomy of Redlichia remains complex, and the distinction between intraspecific variation and interspecific divergence remains poorly resolved. Therefore, conducting a taxonomic revision study of this genus is pivotal to resolving its phylogenetic relationships and refining the existing framework for Cambrian biostratigraphic correlation. Based on the collected materials from the Balang Formation of the Cambrian Stage 4 in Guizhou, China, combined with previously reported specimens, 290 trilobite cephalons of four species of Redlichia(Pteroredlichia), including Redlichia (Pteroredlichia) chinensis lui Chang, 1966, R. (P.) yilongensis Zhang et Lin, 1980, R. (P.) murakamii Resser et Endo in Kobayashi, 1935 and R. (P.) chinensis Walcott, 1905, are selected as research objects. A series of morphometric analysis are conducted, including PCA, CVA, ANOSIM, TPS, MANOVA and traditional metric mathematical statistical analysis. Twelve cephalic linear data are measured to produce eight ratios. The anterior margin width-to-length ratio, previously regarded as diagnostic for separating R. (P.) chinensis lui, R. (P.) murakamii and R. (P.) chinensis, showing extensive overlap in linear regression with no clear morphological differentiation. All other ratios exhibit strong positive linear correlations, similar coefficients, and highly overlapping fitting curves. The 23 landmarks are extracted for visual morphometric analysis of the cranidia. The PCA results demonstrate that the morphological spaces of the four species have extensive overlap, with no distinct differentiation boundaries. This indicates high overall morphological similarity and predominant intraspecific variation. Notably, R. (P.) chinensis exhibits the broadest morphological space, encompassing the variation of the other three species. Consistent with the PCA, the CVA results demonstrate that the morphological space of R. (P.) chinensis has the widest coverage, encompassing the core morphological distribution areas of the other three species. In order to test the accuracy of the geometric morphometric measurements, MANOVA and ANOSIM confirmed significant between-group differences (P < 0.05). Through TPS deformation, it can be visually observed that the interspecific differences among the four species are mainly concentrated in the fixed cheek, palpebral lobe and anterior branch of facial suture. The combined analysis results indicate that the four species, R. (P.) chinensis lui, R. (P.) yilongensis, R. (P.) murakamii, and R. (P.) chinensis, have highly similar morphological structures. Thus, R. (P.) chinensis lui, R. (P.) yilongensis and R. (P.) murakamii should be treated as synonyms of R. (P.) chinensis. The type species of the subgenus Redlichia (Pteroredlichia) will also be revised to Redlichia (Pteroredlichia) chinensis. Redlichia (Pteroredlichia) chinensis has been reported in many regions around the world, and biozones have been established in many areas. The endemic species are merged into R. (P.) chinensis, which can effectively improve the accuracy and reliability of biostratigraphic correlation of the Cambrian stage 4 at regional and global levels, and provide more solid biological markers for the division and correlation of Cambrian strata.