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Evolutionary innovation in the vertebrate jaw: A derived morphology in anuran tadpoles and its possible developmental origin
Author(s) -
Svensson Mats E.,
Haas Alexander
Publication year - 2005
Publication title -
bioessays
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.175
H-Index - 184
eISSN - 1521-1878
pISSN - 0265-9247
DOI - 10.1002/bies.20224
Subject(s) - vertebrate , biology , tadpole (physics) , evolutionary developmental biology , arthropod mouthparts , anatomy , craniofacial , evolutionary biology , skull , gene , genetics , physics , particle physics
Abstract The mouthparts of anuran tadpoles are highly derived compared to those of caecilians or salamanders. The suprarostral cartilages support the tadpole's upper beak; the infrarostral cartilages support the lower beak. Both supra‐ and infrarostral cartilages are absent in other vertebrates. These differences reflect the evolutionary origin of a derived feeding mode in anuran tadpoles. We suggest that these unique cartilages stem from the evolution of new articulations within preexisting cartilages, rather than novel cartilage condensations. We propose testing this hypothesis through a search for similarities in the development of the suprarostral and infrarostral cartilage articulations and of the primary jaw joint. In Xenopus , the gene zax is expressed in a region corresponding to the infrarostral cartilage. This gene is related to the bapx1 ‐gene, which regulates jaw joint development. Further investigation of these genes, as well as other genes with joint‐related functions, in anuran craniofacial development may provide a connection between the morphological diversity seen in the vertebrate head and the corresponding diversity in genetic regulatory processes. We believe that the evolution of larval jaws in anurans may shed light on the general evolutionary mechanisms of how new articulations, not only in the jaw region, could have arisen in the vertebrate skull. BioEssays 27: 526–532, 2005. © 2005 Wiley periodicals, Inc.