A study to be published in a forthcoming issue of the journal Zoologica Scripta has found that seadragons have independently evolved their unusual camouflage more than once.
Nerida Wilson of the Australian Museum and Greg Rouse of the University of California San Diego came to this conclusion after examining the phylogenetic relationships of the Syngnathidae family, which includes pipefishes and seahorses.
The authors used sequences from three mitochondrial gene fragments in their study, and found that the three genera that have been referred to as seadragons (Phycodurus, Phyllopteryx and Haliichthys) did not share a singlemost recent common ancestor (MRCA), with the leafy (Phycodurus) and weedy (Phyllopteryx) seadragons sharing a MRCA, but not with the ribboned seadragon (Haliichthys).
This result supports those of previous studies based on morphology, which also suggest that the seadragons do not form a natural group.
The authors also dated the divergence of the seadragons from other syngnathids, and found the leafy and weedy seadragons diverged from other syngnathids at around the late Miocene (about 8 million years ago), which is considered to be around the time when kelp habitats began to appear.
This made it very likely that habitat association influenced the evolution of the fleshy appendages for camouflage in the seadragons.
For more information, see the paper: Wilson, NG and GW Rouse (2010) Convergent camouflage and the non-monophyly of ‘seadragons’ (Syngnathidae: Teleostei): suggestions for a revised taxonomy of syngnathids. Zoologica Scripta doi:10.1111/j.1463-6409.2010.00449.