Relicts of ancient marine life

This deep-sea creature is long-armed, bristling with teeth, and the sole survivor of 180 million years of evolution

Melbourne: Let us introduce you to Ophiojura, a bizarre deep-sea animal found in 2011 by scientists from the French Natural History Museum, while trawling the summit of a secluded seamount called Banc Durand, 500 metres below the waves and 200 kilometres east of New Caledonia in the southwest Pacific Ocean.

Ophiojura is a type of brittle star, which are distant cousins of starfish, with snake-like arms radiating from their bodies, that live on sea floors around the globe.

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The eight arms, each 10 centimetres long and armed with rows of hooks and spines. And the teeth! A microscopic scan revealed bristling rows of sharp teeth lining every jaw, which we reckon are used to snare and shred its prey.

As per a report in Proceedings of the Royal Society B, Ophiojura does indeed represent a totally unique and previously undescribed type of animal. It is one of a kind — the last known species of an ancient lineage, like the coelacanth or the tuatara.

Researchers compared DNA from a range of different marine species, and concluded that Ophiojura is separated from its nearest living brittle star relatives by about 180 million years of evolution. This means their most recent common ancestor lived during the Triassic or early Jurassic period, when dinosaurs were just getting going.

Since then, Ophiojura‘s ancestors continued to evolve, leading ultimately to the situation today, in which it is the only known survivor from an evolutionary lineage stretching back 180 million years.

Amazingly, researchers have found small fossil bones that look similar to our new species in Jurassic (180 million-year-old) rocks from northern France, which is further evidence of their ancient origin.

Scientists used to call animals like Ophiojura “living fossils”, but this isn’t quite right. Living organisms don’t stay frozen in time for millions of years without changing at all. The ancestors of Ophiojura would have continued evolving, in admittedly very subtle ways, over the past 180 million years.

Perhaps a more accurate way to describe these evolutionary loners is with the term “paleo-endemics” — representatives of a formerly widespread branch of life that is now restricted to just a few small areas and maybe just a single solitary species.

While our new species is from the southwest Pacific, seamounts occur worldwide and we are just beginning to explore those in other oceans.

The Conversation