Soft tissues of the trilobite Palaeolenus douvillei from the early Cambrian Guanshan Biota, South China

Abstract Trilobites, iconic ancient arthropods that endured throughout the Paleozoic Era, are represented by a great number of fossils and a high species richness. However, only a very small number of taxa have their soft tissues preserved, which means that the morphology and ecology of most trilobites have not been specifically determined, even though the morphology of their exoskeletons is well studied. Fortunately, modern technologies (e.g., Micro-CT and μ-XRF) provide non-destructive methods to unveil the soft tissues of fossils that might be buried in rocks. Here we use Micro-CT and μ-XRF to make a detailed study on exceptionally preserved specimens of Palaeolenus douvillei Mansuy, 1912 from the Guanshan Biota. The uniramous antennae, four pairs of post-antennal cephalic appendages, 13–15 thoracic appendages, and at least two pygidial appendages underneath the dorsal shield were revealed for the first time. In addition, we observed that the hypostome and labrum were differentiated in P. douvillei , and this species possesses both typical trilobite digestive systems—namely the crop and digestive glands—simultaneously within a single individual. From the combined evidence of morphological features and phylogenetic analysis, it is reasonable to place P. douvillei within the family Palaeolenidae, thereby contributing new perspectives to the understanding of broader trilobite evolution.