A hypothetical primitive fin structure in fish, believed to be the ancestral form from which modern fish fins evolved and which may relate to the origin of paired limbs in vertebrates.
From Greek archi- (first, chief, primitive) + pterygion (fin). Coined in zoological Latin in the 1870s by anatomists comparing fish fin bones to reconstruct evolutionary history.
This is the fossil-hunting equivalent of finding the 'original receipt'—scientists imagined what the first fin looked like by comparing modern fish, and archipterygium became the name for that hypothetical ancestor that bridges fins to fingers!
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