Maximum a-posteriori phylogeny. The maximum a posteriori tree (black) relating the ten globins of Fig. 5, and 95% confidence intervals of the node heights (grey boxes). Most of the tree's topology is well determined, with the exception of the myoglobin sub-tree. Alpha and beta chain sub-families both support the traditional ordering of birds, turtles and mammals, while the three myoglobin sequences support an unconventional phylogeny, as previously observed by Hedges and Poling . However, the posterior probability for the topology of the myoglobin subtree is smaller than that for the remaining topology. The marginal posterior probability (estimated from the MCMC chain) for the monophyly of human and chicken myoglobin is 83.1%, followed by the conventional grouping of turtle and chicken at 11.9%. The third topologlcal arrangement of myoglobin occurred the remaining 5% of the time, suggesting significant homoplasy in this sub-family.