A long curved bone in the skull of bony fish that connects the shoulder girdle (where fins attach) to the head skeleton.
From Greek kleithron (a bar, bolt, or barrier). Named for its function as a structural bar connecting two major parts of the fish skeleton, reflecting its role as a bracing element.
The cleithrum is one of the most reliable bones for identifying fish fossils—it's found only in ray-finned fish and gives their skulls that distinctive skeletal pattern that makes them instantly recognizable under a microscope.
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