The Early Palaeozoic witnessed the swift emergence and diversification of most animal phyla alongside the establishment of modern-style ecosystems. Exceptionally well-preserved fossils from various Cambrian and Ordovician Lagerstätten provide valuable insights into this pivotal evolutionary phase. Palaeontological investigations describe taxonomic occurrences, anatomical innovations, and developmental patterns, and link these biological observations with characterisations of the abiotic environmental conditions, to achieve a holistic understanding of this time period.

This special volume gathers together publications on Cambrian and Early Ordovician Lagerstätten and provides detailed fossil descriptions for a variety of animals including annelids, arthropods, bryozoans, cnidarians, echinoderms, and scalidophorans. These works showcase the breadth of different approaches that can be applied beyond the descriptive, for example, with evolutionary analyses and studies on ontogeny, development, functional morphology and palaeoecology.

Important new results are revealed from a series of publications studying material from several Cambrian Lagerstätten in China. A new primitive polychaete is described from the Guanshan Biota by Zhao et al., who argue that this annelid likely possessed strong sensory abilities owing to its bicellular eyes and possible nuchal organs. Zhao et al. also describe new bryozoan and cnidarian taxa from the Guanshan Biota, demonstrating that the epibenthic diversity of this Lagerstätte is higher than previously thought. Our understanding of Cambrian ecosystems is also enhanced by the discovery of well-preserved microscopic medusozoans from the Zhangjiagou section. Zhang et al. describe the detailed threedimensional morphology of multiple ontogenetic stages that allow for a complete reconstruction of anatomical shape change during the development of this early cnidarian. The ontogenetic sequence of scalidophorans from the same section is also established in more detail than possible previously based on the discovery of new material described by Qin et al. This study reveals that the sclerites of this undetermined worm became more numerous and increased in size during growth. Our knowledge of Cambrian diversity and development is further enriched by a study conducted by Ma et al., investigating the growth and development of the arthropod Isoxys from the