A venomous arthropod in the Early Cambrian Sea

A number of recently evolved animals possess poison glands for feeding and/or defense. However, examples of such animals are rare in the fossil record. We report a fossil arthropod Isoxys curvirostratus from the Early Cambrian Chengjiang biota of China. This species is regarded as the oldest known venomous arthropod based on the presence of venomous glands in its head region. The adult animal is 2–5 cm long and the body is covered entirely with a carapace. The presence of large stalk eyes and a pair of stout grasping appendages with a terminal spine suggest it was raptorial. Interestingly, the two pear-shaped, three-dimensionally preserved objects that are present in the head region and at the base of the grasping appendages closely resemble the venom glands of some living arthropods in size, shape, and position. These features indicate that the presence of venomous predators could date back 520 million years. Furthermore, our observations suggest that the feeding strategies and organs adapted for this purpose had already reached a high level of diversity and anatomical sophistication in the Early Cambrian ecosystems.