Fig. 3. Evolution of swimbladder and choroid retia mirabilia in jawed vertebrates. Blue and yellow boxes mark the presence of swimbladder and choroid retia mirabilia in living species, respectively. Open boxes indicate the absence of the respective structure, whereas no box indicates missing information. The status of ancestral species has been reconstructed on a composite branching diagram by maximum parsimony. Yellow and blue branches indicate the presence of the choroid and swimbladder rete mirabile, respectively. White and red branches indicate the absence and presence, respectively, of both structures in an ancestral species. The yellow arrow indicates the branch segment along which the choroid rete mirabile first evolved. The blue arrows indicate the subsequent evolution of a swimbladder rete mirabile in four separate groups. Modified after Berenbrink et al. (Berenbrink et al., 2005).