This study presents a novel and ambitious approach to constrain the Early Permian longitudinal position of the South China Block (SCB) using brachiopod paleobiogeography, offering a creative solution to the longstanding challenge of reconstructing paleolongitude in deep-time tectonic models. By integrating quantitative faunal similarity indices (Jaccard, Simpson, and cME) with global plate reconstructions, the authors provide a framework that bridges paleobiology and geodynamics, marking a significant methodological advance. The conclusion that the SCB occupied a central position within the Paleo-Tethys Ocean (as per Young et al., 2019) challenges previous marginal placements and has implications for paleoceanographic and climatic interpretations. The open accessibility of the analytical framework further enhances its utility for future studies.

However, several uncertainties and limitations warrant caution. First, the reliance on brachiopod distribution assumes that faunal similarity inversely correlates with physical distance, yet environmental heterogeneity, larval dispersal barriers (e.g., landmasses, currents), and sampling biases (e.g., uneven fossil preservation/collection) could decouple this relationship. While the authors acknowledge these issues, the extent to which they influence the indices—particularly given the SCB’s disproportionately large dataset—remains unclear. For instance, the Jaccard index’s poor performance highlights the vulnerability of binary presence-absence metrics to sampling disparities, suggesting that results may overemphasize reconstruction Y19’s plausibility.

Second, the tectonic models themselves inherit uncertainties. The assumption of fixed LLSVPs in Matthews et al. (2016) versus their potential mobility in Young et al. (2019) reflects debated geodynamic hypotheses, yet the study does not fully disentangle how these contrasting assumptions propagate into the faunal-distance correlations. Additionally, the choice of 277 Ma as a representative time slice overlooks temporal dynamics within the ~27 Myr Early Permian, during which climatic shifts (e.g., deglaciation) and biotic turnover could skew biogeographic patterns.

A critical but unaddressed issue lies in the taxonomic accuracy of brachiopod genera extracted from the Paleobiology Database. Fossil identifications in large-scale databases are prone to errors due to misclassification, synonymies, or outdated taxonomy. For example, brachiopod genera with overlapping morphological features or poorly preserved specimens may be mis-assigned, directly distorting faunal similarity calculations. Such inaccuracies could artificially inflate or diminish correlations between biogeographic indices and physical distance. To strengthen the robustness of the analysis, future iterations of this framework should involve systematic re-evaluation of the brachiopod taxonomic data by domain experts to resolve ambiguities and validate species assignments. I believe some of the authors are brachiopod experts, not sure if they reviewed the taxonomy of the genera extracted from PBDB.

Lastly, the statistical approach—while rigorous—simplifies complex biogeographic processes into linear relationships. Nonlinear effects (e.g., threshold distances for provinciality) or geographic barriers (e.g., continental shelves) may distort correlations, particularly for marine taxa like brachiopods. The framework’s scalability to other taxa/periods, though promising, requires validation against independent datasets (e.g., paleomagnetic or stratigraphic constraints).

In summary, this work innovatively leverages paleobiogeography to address a critical gap in plate reconstructions, but the conclusions should be tempered by the inherent uncertainties in fossil data completeness, model assumptions, and temporal/spatial resolution. Future studies could strengthen the approach by incorporating multivariate biogeographic methods, higher-resolution time slices, cross-validation with geodynamic models that explicitly test LLSVP mobility, and rigorous taxonomic vetting of fossil datasets.

This interesting and innovative manuscript studies the palaeolongitude of the South China Block (SCB) during the Early Permian by investigating the faunal affinity of brachiopods between the SCB and other tectonic plates. Based on three different paleogeographic reconstructions, the manuscript employs strict statistical analysis to examine the relationship between brachiopod faunal similarities and physical distances. The study supports that the SCB were positioned in the central part of the Palaeo-Tethys Ocean, rather than at its periphery, challenging the conventional views. However, some weaknesses remain in the research methods. Detailed comments/suggestions follow:

1. Comparing faunal affinities between SCB and other plates across the entire Early Permian (spanning ~17 Ma) is problematic. The SCB remained in the palaeoequatorial region throughout this interval, maintaining consistent Tethyan warm-water brachiopods. In contrast, other tectonic units, particularly the Cimmerian Terranes, underwent significant faunal transitions, evolving from Gondwanan cold-water taxa to cool- or even warm-water elements throughout the early Permian. Thus, the brachiopod faunas of these mobile blocks could shift from being very different to closer to those of the SCB over this timespan. To obtain more reliable results, I strongly recommend dividing the early Permian into two intervals (Asselian-Sakmarian and Artinskian-Kungurian) for separate analyses.

2. As noted by the authors, the North American brachiopod faunas exhibit significant diversity during the Early Permian. However, they were excluded from the analyses due to their far distance (>12,000 km) from the South China Block in all three reconstruction maps. The North America Plate was situated in the palaeoequatorial region, and its faunas likely maintained biogeographic connections with South China via ocean currents. Thus, its inclusion in the analyses would provide a more comprehensive assessment of faunal affinities versus distances.

3. Another issue concerns the inconsistent distance thresholds applied in the faunal similarity analyses. In W13 (Fig. 3), the data appear to have a global scope, with distances extending up to 20,000 km. In contrast, Y19 (Fig. 6) restricts the analysis to plates within an 8,000 km distance limit. In addition, relationships between biogeographical indexes and distance based on M16 are absent. What is the basis for the choice of distance limits in these analyses?

4. The authors consider that the latitudinal positions of the SCB were relatively stable in three configurations, its longitudinal variation significantly affects distance-based analyses. However, the latitudinal uncertainties of the SCB affect the distance of other plates to its north and south. For example, the Australian Plate exhibits substantial discrepancies in distance between the SCB in different reconstructions: its centroid ranges between 4000-6000 km in W13, but 6000-8000 km in Y19 and M16. Considering the high diversity of brachiopods of the Australian Plate, the differences in the distance could have a large impact on the results. In addition, the faunal appearances of Western Australia and eastern Australia are really different, it is unclear whether this study treats the Australian Plate as a single plate or divides it into two geographic units.

5. For Fig. 1, I suggest to add the citations and abbreviations in the blank space of each map, such as Young et al., (2019, Y19), which will make the article more readable.

6. For Fig. 2a, I am wondering if the number of plates includes all plates at that range or only those containing brachiopods. Displaying the number of plates with brachiopod records would be more meaningful, as only those would be used in the analysis.