He therefore adopted a classification which divided fish into four groups : Ganoids, Placoids, Cycloids and Ctenoids, based on the nature of the scales and other dermal appendages.
2.
Some displayed unique dermal appendages, such as the feather-like dorsal plumes of " Longisquama ", and the laterally-oriented rib-like rods of " Coelurosauravus ", which supported membranes and may have been used to glide from branch to branch in an arboreal habitat.
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