A team of scientists, including a researcher from the London Natural History Museum have named a new species of ancient sea scorpion (eurypterid), that at around one metre in length was probably a top predator in its marine environment. Named Terropterus xiushanensis, it has been assigned to the Mixopteridae family within the Eurypterida and as such, it is the oldest mixopterid described to date and the first to be associated with Gondwana.

Terropterus xiushanensis life reconstruction.
The newly described eurypterid from the Lower Silurian of southern China (Terropterus xiushanensis) was probably the top predator in the marine ecosystem. Here it is seen attempting to catch some jawless fish. Picture credit: Dinghua Yang.

Terropterus xiushanensis

Writing in the journal “Science Bulletin”, the research team describe this new marine arthropod based on several fossils mostly representing the spiny front appendages, excavated from the Lower Silurian (Llandovery) Xiushan Formation, Xiushan. Two incomplete, but much larger fossils from the roughly contemporaneous Fentou Formation of Wuhan in Hubei Province have also been assigned to the Terropterus genus.

Terropterus xiushanensis fossils
Terropterus xiushanensis fossils (c) close-up of appendage V. Joint 5 or 6 of appendage III, paratype, NIGP 174786 (d). Joint 5 or 6 of appendage III, paratype, NIGP 174787 (e). Coxae, the first segment of a limb, paratype, NIGP 174788 (f). Genital operculum and the genital appendage, paratype, NIGP 174789 (g). Scale bars = 5 mm for (d), (f), (g); 2 mm for (e); 1 mm for (c). Picture credit: Wang et al.

A Formidable Predator

With an estimated length of around 1 metre, (based on the Fentou Formation fossils), Terropterus was far larger than any vertebrate predator known from Lower Silurian strata. Their second, and especially the third, pair of prosomal limbs are enlarged and armed with sharp spines. These limbs were presumably used for capturing prey, trilobites and other invertebrates as well as primitive fish.

Terropterus xiushanensis line drawings.
A line drawing of Terropterus xiushanensis – left dorsal view and right ventral view. Picture credit: Wang et al with additional annotation by Everything Dinosaur.

Mixopterids More Widespread than Previously Thought

Little is known about the evolution and distribution of the Mixopteridae. Only four species in two genera have been described previously and most of the research into these eurypterids took place in the early 20th century. Until the discovery of Terropterus all the mixopterids were associated with the ancient landmass of Laurussia. Terropterus extends the range of this family into marine environments associated with Gondwana.

Members of the Mixopteridae

  • Mixopterus simonsoni 1883 (Estonia).
  • Lanarkopterus dolichoschelus 1899 (Scotland).
  • Mixopterus multispinosus 1921 (New York).
  • Mixopterus kiaeri 1934 (Norway).

Phylogenetic assessment suggests that T. xiushanensis is a sister taxon to L. dolichoschelus.

The researchers note that mixopterids might share a common body plan with highly specialised anterior appendages armed with spines, which presumably played a role in attacking and holding prey, but there are marked differences between the known genera. This might indicate that some mixopterids attacked different kinds of prey.

Terropterus xiushanensis appendages
The holotype (NIGP 174785) appendages of Terropterus xiushanensis. Note scale bar = 5 mm. Picture credit: Wang et al.

The scientific paper: “First mixopterid eurypterids (Arthropoda: Chelicerata) from the Lower Silurian of South China” by Han Wang, Jason Dunlop, Zhikun Gai, Xiaojie Lei, Edmund A. Jarzembowski and Bo Wang published in Science Bulletin.

For models and figures of prehistoric arthropods: Prehistoric Animal Toys and Models.