A rare Cretaceous frog's stomach contents and actualistic experiments uncover a cryptic predator–prey interaction

Most caddisfly larvae construct diverse portable cases that improve survival against predators in freshwater environments through physical protection or crypsis.1 Fossil evidence indicates that such a case-bearing strategy may extend back to the Early Permian,2 with Triassic forms already resembling those of extant lineages.3 The portable case is widely regarded as a key adaptive innovation contributing to the evolutionary success of caddisflies.1 Although caddisfly cases are abundant in palaeo‑aquatic deposits, they are strikingly uncommon in preserved gut contents. Here we describe a caddisfly larval case made of sandy grains located within the stomach region of the Early Cretaceous frog Genibatrachus baoshanensis from northeastern Inner Mongolia, China. We further show experimentally that the African bullfrog (Pyxicephalus adspersus) readily consumes Hydatophylax larvae and that their “stone cases” can remain in the stomach for more than a month. We thus provide direct evidence that G. baoshanensis consumed case‑bearing caddisfly larvae, likely as an instance of opportunistic predation.