Assessment of morphological variation in the early Cambrian trilobite <i>Protoryctocephalus</i>

Studies focused on morphological variation are key for chrono- and biostratigraphy. Morphological variability can be induced by biological and taphonomical biases. Their distinction can become a difficult task due to the lack of population control. Here, we analyse three populations belonging to the genus <i>Protoryctocephalus</i>, two populations from China (<i>P. arcticus</i> and <i>P. balangensis</i>) and a third population of <i>P. arcticus</i> from Greenland. <i>Protoryctocephalus balangensis</i> was collected from the lowermost part of the Kaili Formation where fossils are tectonically deformed while <i>P. arcticus</i> from the ‘Tsinghsutung’ and Greenland specimens are non-deformed. Geometric morphometrics analysis shows that these three populations indeed belong to the same species. However, the large allometry measured in <i>P. balangensis</i> compared with the ‘Tsinghsutung’ population and the Greenland population, which is represented by meraspid and early holaspid individuals, suggested that the morphological variation is taphonomically controlled and non-biological. The results suggest that <i>Protoryctocephalus arcticus</i> from the ‘Tsinghsutung’ Formation is suitable for international correlation, and further studies focus on different aspects such as ontogeny, segment development or fluctuating asymmetry and modularity.