Early Jurassic
During the Early Jurassic, many unrelated basal theropods existed in similar geographic regions, as exemplified through the Kayenta Formation and the Upper Elliot Formation. A hypothesis proposed by Smith "et al." (2007) was that there may have been resource partitioning within different geographic regions of the Early Jurassic based on differences in body size. This hypothesis, with more evidence, would help explain the lack of endemism observed in the fossil record of the Early Jurassic basal theropods.