A fossil “Social Stomach”: Micro‐CT imaging unearths first fossil record of ant proventriculi and comparative analysis with recent species

Eusociality is an extreme form of social behavior found in some invertebrates, especially in ants, which allows them to thrive and dominate the environment through their cooperative and organized behavior. Their complex colony structure and social behavior is provided, among other things, by morphological adaptations, such as the unique structure and a huge variety of proventriculi relative to other insect groups. Here, we report the first discovery of proventriculus by X‐ray microcomputed tomography (µCT) in the fossil ants †Oecophylla brischkei Mayr, 1868 and †Oecophylla crassinoda Wheeler, 1922. This is a remarkable fossil find, as it opens up new perspectives for research on phylogeny, the evolution of ant sociality and feeding behavior. We present a 3D model of the proventriculus in Oecophylla smaragdina (Fabricius, 1775) and a 3D model of the proventriculus in †Oe. brischkei and compare them. Fossil proventriculi are not fundamentally different in structure from the recent. Apparently, already in the late Eocene, the lifestyle and sociality of ants of the genus Oecophylla were similar to the one we are currently observing. For the first time, the structure of the proventriculus of fossil ants is described. Using X‐ray microcomputed tomography methods, the structure of the proventriculi of two species from Baltic amber and their comparison with the recent species of weaver ants Oecophylla smaragdina were studied. Three‐dimensional models reflecting their structure are given. This discovery opens up new opportunities and prospects for work in the field of comparative morphology and the study of the eating behavior of fossil ants and other Hymenoptera.