Multivariate morphometric analysis of faunas may provide a useful estimate of ecologic structure. Tropical bat faunas resemble one another in faunal statistics despite trenchant taxonomic differences, suggesting common evolutionary pressures in three tropical regions. Each fauna consists of many similar closely packed, overlapping, relatively invariable species and a few distinctive, distant, isolated, variable kinds. Temperate and tropical faunas differ in the greater rarity, or even absence, of highly distinctive taxa in the former but are not meaningfully different in packing or degree of overlap.