Commonly used 16S rRNA primers miss much of the archaeal diversity present in the vertebrate gut, leaving open the question of which archaea are host associated, the specificities of such associations, and the major factors influencing archaeal diversity. We applied 16S rRNA amplicon sequencing with archaea-targeting primers to a dataset of samples spanning 5 taxonomic classes (Mammalia, Aves, Reptilia, Amphibia, and Actinopterygii) and obtained from mostly wild individuals. We provide evidence for novel archaea-host associations, including Bathyarchaeia and Methanothermobacter ? the latter of which was prevalent among Aves and correlated with body temperature. Host phylogeny more strongly explained archaeal diversity than diet, while specific taxa were associated with each factor. Co-phylogeny was significant and strongest for mammalian herbivores. Methanobacteria was the only class predicted to be present in the LCAs of mammals and all host species. Archaea-archaea and archaea-bacteria interactions seem to have a limited effect on archaeal diversity.