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.
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.
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.
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.
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.