The results indicate that a second, distal phase of Hoxd gene expression is not uniquely associated with tetrapod digit development, but is more likely a plesiomorphic condition present the common ancestor of chondrichthyans and osteichthyans. We propose that a temporal extension, rather than de novo activation, of Hoxd expression in the distal part of the fin may have led to the
http://plosone.org/article/info:doi/10.1371/journal.pone.0000754#article1.front1.article-meta1.abstract1.p1
This is an important study revising the way we view the evolution of the autopod and the role of Hox genes in the fin-to-limb transition. The take-home lesson is given all the more credence by a conceptually similar analysis, that was published while this study was in preparation, that examined Hox expression in the fin buds of ray-finned fish (the paddlefish), and reached the same conclusion (Davis et al 2007).
