/kro sop'teuh rij"ee euhn/ , n.
1. any fish of the group Crossopterygii, extinct except for the coelacanth, regarded as being ancestral to amphibians and other land vertebrates.
adj.
2. pertaining to or resembling a crossopterygian.
[ 1860-65; Crossopterygi ( i ) group name ( kross ( oí ) tassels, fringe + -o- -O- + pterýgi ( on ) little wing or fin, equiv. to pteryg- (s. of pterýx ) wing, fin + -ion dim. suffix) + -AN ]