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They found the unusual head-shoulder joint bears similarities with the gill arches in earlier fish, suggesting it was these that were retained and incorporated into the formation of the shoulder at an early stage.

The vertebrate shoulder, they conclude, arose in part from ancestral fishes’ gill arches, curved supports encircling the throat.

Metaspriggina boasted seven pairs of rod-like structures called gill arches, or branchial arches, that functioned for both filtration of food particles and respiration.

It is not the oldest shark fossil, but it is the oldest to reveal all of the anatomy of the skeleton supporting the gill arches, a vitally important element of a fish.

The X-ray scans revealed the fossil had complete gill arches, the support structures for the gills that fish use to breathe.