Gill Skeletons (IMAGE)
Caption
The shark arch gill skeleton (left) shows primitive gill rays that are found only in sharks and other cartilaginous fishes. The gills of other fishes (right) are also arched but lack gill rays. This primitive feature of sharks allowed the researchers to link the developmental genetic program for fins and limbs to the more primitive one for gill rays.
Credit
Image by J. Andrew Gillis, University of Chicago
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