Fig. 3.—

Schematic phylogenetic tree demonstrating the presence or absence of COX8 across the vertebrate phylogeny. Letters above each branch indicate the presence of the relevant COX8 isoforms. Non: total absence of all COX8 isoforms. Notably, the suborders Iguania and Serpentes are labeled. The topology of the tree is adopted from NCBI Taxonomy (see URL in Material and Methods), which is also consistent with a recently published phylogenetic study (Vidal and Hedges 2009). *represents detection of COX8 in the genome sequence of the relevant organism.