A clade credibility tree showing the relationships between lungfish and other selected vertebrate opsins. The tree was generated using Bayesian inference via a Metroplis-coupled Markov chain Monte Carlo simulation. Sarcopterygian fish (coelacanth and lungfish) are in red, teleost fish are in blue, amphibians are in green and reptiles are in maroon. Genbank accession numbers are listed in Table 1. Posterior probability values are at the base of each node. The rh4 opsin of Drosophila melanogaster is used as an outgroup (Table 1). The probability of most relationships within the tree is 1.00 after 300,000 generations, while lower posterior probability values are found within the lws and rh1 groups.