A basic ecological tenet is that organisms in a community occupy different niches and have different traits, but how consistently competition, selection, and phylogenetic effects structure communities remains uncertain. Are all communities created equal? We examine how mammalian carnivoran communities are assembled with regard to mass, diet, and locomotion. Here, we use a multivariate nearest-neighbor framework to examine multiple North American localities spanning 3 million years to determine whether community assembly is consistent through time and four modern localities around the world to assess the effects of habitat. Additionally, we examined how trait patterns differ among families and how family-level evolutionary effects affect them. We found some broadly consistent patterns, although differences are more pronounced than similarities. Diet is more affected by evolutionary constraints than by time or place. Locomotion is most affected by habitat, and the ability to partition niches is related to habitat heterogeneity. Mass is influenced by family, but also by habitat and the mass-selective extinction events at the end-Pleistocene. These findings indicate that assembly patterns are not largely determined by within-community interactions but instead show that each community is a product of its independent variables.