Trait-based paleontological niche prediction suggests ecological turnover across the KPg boundary in predatory ants

The earliest fossil ants known represent a morphologically diverse assemblage of lineages, with some taxa exhibiting specializations not present today, and others mirroring modern phenotypes. These species are known from fossil amber ranging from 100-78 million years ago: after the Cretaceous extinction ~66 million years ago, many of these morphologically bizarre groups disappeared from the fossil record and were replaced by extant lineages, which rapidly increased in diversity and abundance during the Cenozoic. Among the most unusual of these extinct lineages were haidomyrmecines, or "hell ants", a group possessing vertically-aligned trapjaw morphology and cephalic horns. What niches or roles were they occupying that might have made them more vulnerable to extinction? Through a comprehensive morphometric dataset and machine learning tools, we predict the ecological niches of hell ants, and compare their ecospace occupation to present-day trapjaw lineages. We find that hell ants were most likely ground and leaf-litter predators, and occupied ecospace that at least partially overlaps with all other known trapjaw lineages' ecospace occupation, suggesting faunal turnover in niche occupation consistent with the hypothesis of dynastic succession in ant lineages through time.