The Phacopida are a representative order of trilobites from the Ordovician to the Devonian periods, occupying an important position in the marine ecosystem during the early Phanerozoic spannedmany significant geological events in the Paleozoic. The taxonomic diversity of Phacopida has been well investigated, but the co-evolution of its morphological disparity with geological events still needs to be clarified. This study focuses on the morphological evolution of Phacopida trilobites and its response to geological events ranging from the Ordovician to Devonian. Utilizing a geometric morphometric approach, we analyzed the shape of cephalon of 351 distinct genera and quantified the morphological changes of Phacopida from the Ordovician to Devonian based on morphospaces. We found that the peak of morphological disparity in the cephalon of Phacopida occurred in the Darriwilian and the Eifelian, and there were three major recessions, respectively: the Katian, the latest Silurian, and the Famennian, all of them appeared in periods of major environmental disturbances such as anoxic events and regressions, suggesting that the morphological evolution in the cephalon of Phacopida was closely related to oxygen content in sea water and the changes of sea level, and these environmental factors greatly affected the variation of their morphological disparity. Meanwhile, the number of new genus of Phacopida decreased during the Eifelian, but morphological disparity in the cephalon(SOV and SOR) increased in the same time, which means the peak of morphological disparity appeared after the peak of taxonomic diversity. This could be because the rising Eifelian competitors which have similar ecological niche of Phacopida, restrained the taxonomic diversity of Phacopida, but these competitors has also increased competition between species in the same ecological niche and promoted the morphological innovation in the cephalon of new species of Phacopida.

The Ordovician of the Ordos Basin, with huge resource potential, has been a key target for natural gas exploration in recent years. However, the correlation of Ordovician lithostratigraphic units in the Ordos Basin is somewhat controversial, so it is urgent to conduct a detailed stratigraphic comparison based on available paleontological data. This paper synthesizes the previous research on conodont and graptolite biostratigraphy and establishes the correlation of the Ordovician within the basin. On the basis of biostratigraphic dating, this paper suggests that the Sandaokan, Zhuozishan, Kelimoli and Majiagouformations belong to the Darriwillian, Middle Ordovician, while the Lashizhong and Pingliangformations belong to the Upper Ordovician. The biostratigraphic studies of the Lower Ordovician in the basin are relatively insufficient. In the Lower Ordovician of the western margin, the conodont zones of R. manitouensis and G. quadraplicatus in the Tremadocian can be identified, and on the eastern margin, the P. obesus Conodont Zone was discovered, which can be correlated with the top of the Liangjiashan Formation on the southwestern margin. The biostratigraphic studies of the Middle and Upper Ordovician in the basin are much comprehensive. The conodont zone of Histiodella cf. holodentata recognized at the top of the Sandaokan Formation can be correlated with the D. costodus zone in the Machuan Formation on the southern margin and inthe Majiagou Formation on the eastern margin. From the Kelimoli to the Gongwusu Formation, the conodont zones from D. tablepointensis to B. compressa and the graptolite zones from P. elegans to N. gracilis were identified, which can be correlated with the middle-upper part of the Shuiquanling Formation to the middle of the Pingliang Formation on the southwestern margin and the middle-upper part of the Majiagou Formation to the top of the Fengfeng Formation on the middle-eastern margin, indicating a Darriwillian to Sandbianage. The graptolite zone of C. bicornis was recognized from the Lashizhong to Sheshan Formation on the western margin, which can be correlated with the middle of the Pingliang Formation on the southwestern margin and from the top of the Jinghe Formation to the bottom of the Zhaolaoyu Formation on the southeastern margin, suggesting amiddle-late Sandbianage. Both the Taoqupo Formation on the southwestern margin and the Beiguoshan Formation on the southeastern margin of the basin yield conodont species Y. neimengguensis and Y. yaoxianensis of the Katian, showing a correlation between them.

Reconstructing paleo-temperatures is of great significance for understanding the Earth's climate changes and the evolution of life. Traditional thermometry based on δ¹⁸O has uncertainties due to its reliance on the oxygen isotope composition of seawater (δ¹⁸O_w). Carbonate clumped isotope (Δ₄₇) thermometry, which was developed over the past 20 years, has become a research hotspot as it does not require prior knowledge of δ¹⁸O_w. However, carbonates, which are the most commonly used material for Δ₄₇ thermometry, are highly susceptible to diagenetic alteration, sometimes leading to the loss of original temperature information. Therefore, apatite, which contains structurally bound carbonate and exhibits strong resistance to diagenetic modification, has been an ideal material for studying deep-time paleoclimates. This paper reviews the research on apatite clumped isotopes, discussing the issues in the calibration relationships between apatite Δ₄₇ and temperature, as well as potential kinetic effects. Additionally, factors such as organic matter content, kinetic effects, and diagenetic processes (recrystallization and solid-state reordering effects) may all introduce biases in thermometric results. In the future, it will be necessary to refine the calibration relationships, integrate multi-isotope and trace element analyses to enhance data reliability. With further research, apatite clumped isotope technology is expected to bring breakthroughs to studies in deep-time paleoclimatology and related fields.