superfamilies

A superfamily is a taxonomic rank used in some biological classifications to group related families within an order. It sits above the family level and below the order, and it is intended to reflect a common ancestry and broader evolutionary relationships among the member families. Not all classification schemes use the rank, and the definitions and boundaries of a superfamily can vary among groups and databases.

In zoological taxonomy, an example is the superfamily Hominoidea within the order Primates. Hominoidea includes the families Hominidae (great apes) and Hylobatidae (gibbons). Other examples exist in different lineages, but the use and delimitation of superfamilies can be inconsistent across groups.

In molecular biology and bioinformatics, "superfamily" refers to a large group of protein families that share a common structural framework and a distant evolutionary origin. Members may have diverged in sequence, but exhibit related three-dimensional folds and conserved functional motifs. Structural classification systems such as SCOP and CATH organize proteins into superfamilies based on fold and evolutionary relationship. Classic exemplars include the Rossmann superfamily, the TIM-barrel superfamily, and the P-loop NTPase superfamily.

Classification at the protein level is typically supported by structural comparisons, sequence-profile similarity, and occasionally phylogenetic analyses, rather than straightforward sequence identity thresholds. In both biology and biomedicine, recognizing superfamilies helps illuminate evolutionary history, predict functions for uncharacterized proteins, and organize large, diverse families into coherent groups.