New eurypterids from the Lower Devonian Nagaoling Formation of Guangxi, South China

Abstract

Eurypterids, commonly known as sea scorpions, were an extinct group of arthropods renowned for their large size and role as apex predators in Early Paleozoic marine ecosystems. Among them, carcinosomatids and pterygotids stand out as two particularly striking groups, both characterized by their large size but differing in morphological specialization. Compared to their diversity and abundance in Laurussia, both groups are rare in the larger Pan-Gondwanan region, which is consistent with the general pattern observed from most eurypterids, especially the Devonian genera. Here, we report a new diverse eurypterid fauna from the Nagaoling Formation (Lochkovian, Devonian) in Guangxi, South China, including Carcinosomatidae, Pterygotidae, and Adelophthalmidae. Tigrisopterus zengi n. gen. n. sp. represents the youngest known carcinosomatid worldwide and the first Devonian member of this family discovered outside Laurussia. Acutiramus sp., with an estimated body length of approximately 1.6–1.8 m, is the first Acutiramus component found in China and one of the youngest representatives of this genus known to date. These two families, along with the generalist Adelophthalmus found in the same bed, suggest a complex ecological structure in the Devonian shallow marine environment of South China. This discovery expands both the temporal and spatial distribution of carcinosomatids and pterygotids, providing new insights into the distribution and evolutionary history of these ancient predators.