Fossils of Giant Sea Scorpion Found in China


A new genus and species of mixopterid eurypterid (sea scorpion) has been identified from several fossil specimens found in the Xiushan Formation, China.

Life reconstruction of Terropterus xiushanensis. Image credit: Dinghua Yang.

Life reconstruction of Terropterus xiushanensis. Image credit: Dinghua Yang.

Terropterus xiushanensis lived approximately 435 million years ago during the Llandovery epoch of the Silurian period.

The ancient marine creature belongs to a family of sea scorpions called Mixopteridae.

“Eurypterids, or sea scorpions, are an important group of mid-Paleozoic chelicerate arthropods whose evolution and paleoecological significance have attracted much attention in recent years,” said Professor Bo Wang from the Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment at the Chinese Academy of Sciences and colleagues.

“One of the most remarkable eurypterid families is Mixopteridae, whose members are quite large and superficially scorpion-like eurypterids bearing highly specialized anterior appendages.”

“Their second, and especially the third, pair of prosomal limbs are enlarged and very spiny. These limbs were presumably used for prey-capture, and analogies can be drawn with the ‘catching basket’ formed by the spiny pedipalps of whip spiders among the arachnids.”

“Our knowledge of these bizarre animals is limited to only four species in two genera described 80 years ago: Mixopterus kiaeri from Norway, Mixopterus multispinosus from New York, Mixopterus simonsoni from Estonia, and Lanarkopterus dolichoschelus from Scotland.”

“All are Silurian in age and come exclusively from the ancient continent of Laurussia, which constrains our knowledge of the morphological diversity, geographical distribution and evolutionary history of the group.”

Terropterus xiushanensis represents the first mixopterid from the ancient supercontinent of Gondwana as well as the oldest known mixopterid.

Specimens and reconstruction drawing of Terropterus xiushanensis: (a) appendages II-VI, holotype; (b) reconstruction drawing of Terropterus xiushanensis, dorsal and ventral views; (c) close-up of appendage V; (d) joint 5 or 6 of appendage III, paratype; (e) joint 5 or 6 of appendage III, paratype; (f) coxae, paratype; (g) genital operculum and the genital appendage, paratype. Scale bars - 5 mm in (a), (d), (f), and (g); 2 mm in (e); 1 mm in (c). Image credit: Wang et al., doi: 10.1016/j.scib.2021.07.019.

Specimens and reconstruction drawing of Terropterus xiushanensis: (a) appendages II-VI, holotype; (b) reconstruction drawing of Terropterus xiushanensis, dorsal and ventral views; (c) close-up of appendage V; (d) joint 5 or 6 of appendage III, paratype; (e) joint 5 or 6 of appendage III, paratype; (f) coxae, paratype; (g) genital operculum and the genital appendage, paratype. Scale bars – 5 mm in (a), (d), (f), and (g); 2 mm in (e); 1 mm in (c). Image credit: Wang et al., doi: 10.1016/j.scib.2021.07.019.

The species was relatively large, reaching up to 1 m (3.3 feet) in length, and had a ‘particularly enlarged prosomal limb III, characterized by a unique arrangement of spines.’

It likely played an important role of top predators in the Silurian marine ecosystem when there were no large vertebrate competitors.

“The paleogeographical distribution of mixopterids was rather limited until now and no examples of this group have been previously discovered in Gondwana,” the paleontologists said.

“Our 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.”

The study was published in the journal Science Bulletin.

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Han Wang et al. 2021. First mixopterid eurypterids (Arthropoda: Chelicerata) from the Lower Silurian of South China. Science Bulletin 66 (22): 2277-2280; doi: 10.1016/j.scib.2021.07.019

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