A paper co-written by Professor of Biology Ann Burke, “Body wall development in lamprey and a new perspective on the origin of vertebrate paired fins,” was published in the July issue of the Proceedings of the National Academy of Sciences.
Burke and her colleagues investigated the sea lamprey and the Japanese lamprey, comparing “the embryonic development of both these jawless fish to jawed animals — a shark, the catshark, and a salamander, the axolotl.” The abstract of the paper states, “Classical hypotheses regarding the evolutionary origin of paired appendages propose transformation of precursor structures (gill arches and lateral fin folds) into paired fins. . . . We focus on the evolutionary history of the somatopleure to gain insight into the tissue context in which paired fins first appeared. Lampreys diverged from other vertebrates before the acquisition of paired fins and provide a model for investigating the preappendicular condition. We present vital dye fate maps that suggest the somatopleure is eliminated in lamprey as the LPM is separated from the ectoderm and sequestered to the coelomic linings during myotome extension. We also examine the distribution of postcranial mesoderm in catshark and axolotl. In contrast to lamprey, our findings support an LPM contribution to the trunk body wall of these taxa, which is similar to published data for amniotes. Collectively, these data lead us to hypothesize that a persistent somatopleure in the lateral body wall is a gnathostome synapomorphy, and the redistribution of LPM was a key step in generating the novel developmental module that ultimately produced paired fins. These embryological criteria can refocus arguments on paired fin origins and generate hypotheses testable by comparative studies on the source, sequence, and extent of genetic redeployment.”