Hallucigenia: as reconstructed in the 1970s (left) and later (right). Images from the Smithsonian.

One of the most interesting of Cambrian fossil creatures is the aptly named Hallucigenia (see above). Famously, Hallucigenia fossils were once reconstructed back to front and upside down, with the spines on the animal’s back seen as bizarre stilt-like legs, and the actual legs seen as strange tentacles. Later reconstructions addressed these errors, but still showed unrealistic stilt-like locomotion.

Hallucigenia is now seen as a close relative of the onychophorans (velvet worms), so that adding spines to the photograph below would give a better indication of appearance. A fascinating recent paper in Nature by researchers at Cambridge clarifies the relationship by showing that a key feature of Hallucigenia’s claws – their construction from stacked elements – resembles that of the jaws and claws of modern onychophorans. This makes Hallucigenia no less nightmarish, but a great deal more comprehensible!

A modern onychophoran (velvet worm). Photo by Martin Smith.

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