The weird and wonderful of the Cambrian (Part 14): Opabinia – the five-eyed enigma of the Cambrian seas

Jon Trevelyan (UK)

This is the fourteenth in my series of short articles on fossils of the Cambrian. Few Cambrian animals have captured the public imagination and baffled palaeontologists quite like Opabinia regalis, an extraordinary creature from the Middle Cambrian Burgess Shale. With its five eyes, backwards-facing mouth, and a long, flexible proboscis tipped with spines, Opabinia has become a symbol of the experimental nature of early animal evolution.

Its strangeness is no exaggeration. Even at the time of its first reconstruction, the distinguished palaeontologist Harry Whittington was said to have elicited laughter from the audience when he revealed its anatomy slide. A century after its discovery, it remains one of the most iconic and perplexing animals of the Cambrian Explosion.

What Opabinia looked like

Opabinia was a small, soft-bodied animal, roughly 4-7cm long, with a flattened, elongate body ideal for life close to the seafloor. It possessed five stalked eyes clustered on top of its head, almost certainly used to scan for movement on all sides, in dimly lit waters. But its defining feature was the long, hose-like proboscis, ending in a grasping claw. This remarkable appendage was capable of extending, flexing and picking up small items from the sediment.

Running along its sides were lateral flaps, arranged in overlapping pairs. These flaps were used for swimming through undulating movements, rather like those of modern cuttlefish, while the fan-like tail probably helped steer and stabilise the animal. Opabinia also had a series of dorsal lobes supporting its digestive system, suggesting a more complex internal arrangement than many of its contemporaries.

How it lived

The Burgess Shale preserves Opabinia in exquisite detail, allowing researchers to infer much about its ecology. Its anatomy strongly suggests a benthic lifestyle, gliding quietly just above the seafloor. The flexible proboscis was almost certainly used to probe the sediment for small, soft-bodied prey, perhaps worms, larvae or decaying organic material.

Its backwards-facing mouth indicates that food collected by the proboscis had to be swept underneath the body and pushed towards the head, which is another uniquely early-experiment feature in Cambrian anatomy. Opabinia lacked obvious defensive structures, implying that it survived through stealth, speed or by occupying ecological niches that avoided the more heavily armoured predators such as Anomalocaris.

What Opabinia tells us about evolution

Opabinia belongs to an extinct group of animals known as the stem-arthropods, representing an early side branch of the lineage that eventually led to true arthropods (insects, crustaceans, spiders, trilobites and so on). Its odd mixture of traits, including arthropod-like flaps, soft non-segmented head and bizarre feeding apparatus, reflects evolutionary experimentation during a period when animal body plans were still being “tested”.

This makes Opabinia profoundly important: it shows that early arthropod evolution was not a simple, linear path, but a proliferating tree of unusual anatomies, only some of which survived the pressures of natural selection.

Preservation and rarity

Opabinia comes exclusively from the Burgess Shale, where exceptional preservation conditions allowed soft tissues to be replicated in fine muds. Only a small number of specimens are known, making it a rare but exceptionally informative fossil. Its delicate nature ensures that, without the unique mudslide burial events associated with the Burgess Shale, Opabinia would almost certainly have vanished without a trace.

Why it matters

Opabinia endures as one of the great examples of how alien early life could appear. Its graceful body, peculiar eyes and improbable proboscis challenge assumptions about what animals “should” look like. More importantly, it acts as a reminder that the diversity of life is often shaped by experiments that do not persist, but leave tantalising fossils hinting at the breadth of ancient possibility.