Ancient dog-sized scorpion fossil discovered in China

Imagine a scorpion! What usually comes to mind is a reasonably small, finger-length, venomous creature who primarily inhabits the land. But imagine diving into a sea and coming face-to-face with a meter-long scorpion!

Scientists from the Nanjing Institute of Geology and Palaeontology recently unearthed a fossil of a scorpion that roamed the sea floors of south China. Fortunately, the dangerous creature—16 times longer than the average-sized extant scorpions—lived at least 400 million years ago, and not now!

Named Terropterus xiushanensis, this dog-sized arachnid was a relative of the present-day horseshoe crab and whip spider. It had similar spiny attacking forelimbs and belonged to mixopterids—a group of eurypterids (sea scorpions)—also recognised for their specialised arms, used for catching prey.

“Our knowledge of mixopterids is limited to only four species in two genera, which were all based on a few fossil specimens from the Silurian Laurussia 80 years ago,” explained the authors of the study. The well-preserved fossils form new evidence to understanding the morphological diversity of mixopterids.

The fearsome beast is suspected of having lived during the Silurian period—somewhere between 443.8 million and 419.2 million years ago—where it would have been an apex underwater predator that used its giant spiny arms called pedipalps to prowl on fish and molluscs.

Earlier, research had suggested that sea scorpions were the top predators long before the evolution of barracudas or sharks. Based on the fossil specimen of eurypterids, researchers had deduced that sea scorpions used their tails, weaponized by their serrated spiny tips, to dispatch their prey.

However, T xiushanensis is the first mixopterid reported from the Gondwana supercontinent. Gondwana formed when the large landmass of Pangaea split into two, thereby suggesting an under-collecting bias in the group.

“Future work, especially in Asia, may reveal a more cosmopolitan distribution of mixopterids and perhaps other groups of eurypterids,” say the researchers.

The study will be published in the November issue of the Science Bulletin, and its online version can be accessed here.