Tests of Amino Acid Frequency Homogeneity[i] for all 13 Genes within Selected Groups of Vertebrate Taxa
| Group | X 2 | P |
| All taxa | 1010.03 | <0.001 |
| Non-amniotes | 211.30 | 0.128 |
| Amniotes | 392.91 | 0.985 |
| Non-mammals | 321.12 | 0.012 |
| Mammals | 237.09 | 1.000 |
| Endotherms | 328.11 | 0.999 |
| Ectotherms | 277.41 | 0.014 |
| Fishes | 61.51 | 1.000 |
| Amphibians | 20.40 | 0.371 |
| Reptiles (including birds) | 108.11 | 0.638 |
| Reptiles (not including birds) | 21.89 | 0.290 |
| Birds | 10.30 | 0.945 |
[i] The null hypothesis is that amino acid frequencies are not different among all taxa within a particular group; Pvalues <0.05 indicate significant heterogeneity within the group.