Morphological innovation through gene regulation: an example from Devonian Onychodontiform fish

The recent development of novel phenotypic designs by changes in gene regulation has been extensively discussed within the context of evolution and development. The fossil record shows many new designs (or body plans) which appear rapidly at various stratigraphic levels. One example of this is the arrival of the lobe finned fish in the Early Devonian, when a great variety of new forms appeared. These include the dipnoans, the onychodontids, the porolepiforms and the osteolepiforms, which differ widely in a number of characters. Each of these groups originated from an unspecified sarcopterygian source and they have since evolved independently. They also carry over the primitive genes of the parent or parents and similar changes in these genes will not produce synapomorphies between members of the different lineages. Unless care is exercised, homoplasies will be used as synapomorphies. Evidence must be found to find groups of features that define uniform functional entities. These define monophyletic groups. Recognition of homoplasy of characters thus becomes important. The study of the new functional structures and the areas from which they were derived by changes in gene regulation, would give us more evolutionary information.