Eurypterids (Arthropoda: Chelicerata), normally known as sea scorpions, are an important extinct group of Paleozoic chelicerate arthropods. As a star animal in the Silurian sea (about 430 million years ago), its evolutionary history and paleoecological significance have always attracted attentions of both researchers and the public. 
Mixopterids are a remarkable group of eurypterids characterized by extremely specialized prosomal appendages. These limbs were presumably used for prey-capture, like the ‘catching basket’ formed by the spiny pedipalps of whip spiders. However, in contrast to their popularity, our knowledge of these bizarre animals is limited to only four species in two genera which all based on a few fossil specimens from the Silurian Laurussia 80 years ago.
Recently, postgraduate WANG Han, Prof. WANG Bo and other researchers from China, German and England described a new mixopterid, Terropterus xiushanensis gen. et sp. nov. from the Lower Silurian of South China. Their finding represents the first mixopterids in Gondwana, and also the oldest mixopterids. The research expanded our understanding of the morphological diversity and geographical distribution of mixopterids. The research results were recently published as a cover paper in the international academic journal Science Bulletin.
Terropterus is relatively large, estimated to have been nearly a meter in length. It bears particularly enlarged prosomal limb III, characterized by a unique arrangement of spines on it. The well-preserved appendages and other body parts fossils provided new evidences for expanding morphological diversity of Mixopteridae. By morphological comparison and phylogenetic analysis, researchers suggested more complex evolutionary relationships of this group than previously thought.
Terropterus, a large arthropod with "sharp weapon", may have been playing an important role of top predators in Early Silurian shallow marine of South China. Meanwhile, the first Gondwanan mixopterid- along with other eurypterids from China and some undescribed specimens- suggests an under-collecting bias in this group. Future work, especially in Asia, may reveal a more cosmopolitan distribution of mixopterids and perhaps other groups of eurypterids.
This research was supported by the Chinese Academy of Sciences and the National Natural Science Foundation of China. Mr. YANG Dinghua (from NIGPAS) made the artist’s reconstruction.
Reference: Wang Han *, Dunlop J., Gai Zhikun, Lei Xiaojie, Jarzembowski E. A., Wang Bo *, First mixopterid eurypterids (Arthropoda: Chelicerata) from the Lower Silurian of South China, Science Bulletin, https://doi.org/10.1016/j.scib.2021.07.019
Fig.1 Cover image of Science Bulletin. (Reconstruction drawing by Dinghua Yang)
Fig.2 Terropterus xiushanensis. (a, c, d, e, f: appendages; b: reconstruction drawing, dorsal and ventral views; g: genital operculum and the genital appendage)
Fig. 3 Result of the phylogenetic analysis. (The position of Terropterus xiushanensis is highlighted in blue)
Contact:
LIU Yun, Propagandist
Email: yunliu@nigpas.ac.cn
Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences
Nanjing, Jiangsu 210008, China
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