Hirnantian costate craniides are rare in the world; many have only been defined using open taxonomic nomenclature and assigned to the genera Acanthocrania and Philhedra. New material from South China and Myanmar allows establishment of a new genus, Xenocrania, including its type species Palaeocyclus? haimei Reed from the Hirnantia fauna in northern Shan State, Myanmar. This genus is characterized by a unique ornamentation with a large degree of intraspecific variation in sympatric and allopatric populations. Three types of ornamentation (A, B and C) are recognized within the same population of this species, and even on the same individual. Based on this high degree of variation, we consider Xenocrania haimei and Acanthocrania yichangensis Zeng from the Hirnantia fauna of Yichang, western Hubei, South China to be conspecific. X. haimei was probably an opportunistic species, exhibiting considerable significant phenotypic pleiotropy (exemplified by a highly variable ornament) in response to severe ecological stress, particularly during the end Ordovician crisis, enabling the species to survive the extinction event. Geographically, Xenocrania gen. nov. occurs not only in the Hirnantia fauna of Myanmar (Sibumasu) and South China, but also in England (Avalonia), Poland (Baltica) and probably also Bohemia (Perunica). A further reassessment of many nominal or indeterminate taxa of Ordovician and Silurian craniides tentatively attributed to Philhedra, Acanthocrania and other related genera is needed.

Abstract‘Strophodontoid’ brachiopods represented the majority of strophomenide brachiopods in the Silurian and Devonian periods. They are characterized by denticles developed along the hinge line. The evolution of denticles correlated with the disappearance of dental plates and teeth and were already present when the clade originated in the Late Ordovician. Specimens of Eostropheodonta parvicostellata from the Kuanyinchiao Bed (early–middle Hirnantian, uppermost Ordovician) in the Hetaoba Section, Meitan, Guizhou Province, South China, display clear fossil population variation, during a process of loss of dental plates and the development of denticles. Three phenotypes of E. parvicostellata are recognized in a single fossil bed, likely heralding a speciation process. Non‐metric multidimensional scaling (NMDS) based on five key characters of genera of the Family Leptostrophiidae shows a much wider morphospace for Silurian genera than for those in the Devonian. Phylogenetic analysis of the Family Leptostrophiidae supports the NMDS analysis and mostly tracks their geological history. The fossil population differentiation in E. parvicostellata discovered between the two phases of the Late Ordovician mass extinction event (LOME) linked to a major glaciation, suggests a Hirnantian origination of the ‘strophodontoid’ morphology, and links microevolutionary change to a macroevolutionary event.

Linguliform brachiopods are a minor but distinctive component of the Palaeozoic Evolutionary Fauna. However, there is no formal research on Katian (Late Ordovician) linguliform microbrachiopods in South China. Fossils from the 'Pagoda', 'Linhsiang' and Daduhe formations, Wanhe section of Yunnan Province, South China, provide a unique opportunity to bridge the gap. Here, we report and systematically describe, for the first time, a deep-water Katian linguliform microbrachiopod association, including 13 species assigned to nine genera, namely Paterula cf. numerosa Popov,

Atrypoidea is a Silurian smooth atrypide with a worldwide distribution and high species-level diversity especially during Ludlow to Prídolí. In this study, the occurrences of 67 species, 14 subspecies, and 23 forma, cf., aff., or var. species are summarized. Among them, Atrypoidea recta from Aeronian of Siberia is the earliest known occurrence of this genus, while Atrypoidea elatior or Atrypoidea polaris modica from upper Prídolí strata of the Czech Republic and China, respectively, should be the youngest species. No valid Devonian occurrence of Atrypoidea has been recorded due to absence of convincing identification or poor stratigraphic information. The rapid evolution and cosmopolitan nature of Atrypoidea allow some species to be used as index fossils for strata of Ludlow and Prídolí in South China. The age of the Chejiaba Formation in Guangyuan, Sichuan Province, South China, has been clarified based on the occurrence of Atrypoidea. Specimens from this locality, which are preserved in situ, are described herein and illustrated with reconstruction of life style for the first time.