A new social insect nest from the Upper Cretaceous Kaiparowits Formation of southern Utah

A fossilized social insect nest, Socialites tumulus new ichnogenus and ichnospecies, is described from continental strata of the Upper Cretaceous Kaiparowits Formation in southern Utah. Nine discrete nest structures are preserved along a single bedding plane, within an area of about 25 m 2 . Fine-grained, ripple-laminated sandstone, interpreted as a fluvial crevasse splay deposit, drapes the nest structures and is thought to have rapidly buried and preserved much of the aboveground architectural morphology of the nest structures. Such social insects as ants and termites are considered as possible tracemakers. Comparison to fossil and modern nests suggests that Socialites tumulus is more similar to nests produced by ants than by termites. This trace fossil preserves rare, tangible evidence of nest construction by social insects during the Late Cretaceous, adding new information on insect diversity and habitat utilization in Mesozoic terrestrial ecosystems. Detailed study of these complex nest structures also aids in paleoenvironmental reconstruction, revealing multiple phases of nest construction, burial, and reestablishment. FIGURE 1—Locality map with inset map showing the spatial distribution of nests T1–T9 along a single bedding plane.