Mesozoic rocks with exceptional preservation of marine arthropods are known worldwide but largely restricted to high latitudes. The scarcity of assemblages with exceptional preservation in low latitudes greatly limits our understanding of the origins of several modern groups and the evolution of tropical biotas through time. Here we report the oldest Cumacea, or “comma” shrimp (Arthropoda: Eumalacostraca: Peracarida) with modern affinities, from a new mid-Cretaceous (95–90 Mya) Lagerstätte in tropical South America. Cumaceans have one of the poorest fossil records among marine arthropods, despite today being abundant and speciose benthic organisms associated with fine-grained sediments with high fossilization potential. Eobodotria muisca gen. et sp. nov., found in mass-accumulation surfaces, preserves with stunning detail the gut, mouth parts, legs, pleopods, uropods bearing setae, antennal flagella, and even small eyes bearing ommatidia. These features, rarely preserved in fossil crustaceans, plus the large sample size (>200 individuals, ~8 mm long), allow us to discuss phylogenetic/systematic aspects of the oldest modern cumacean known, and explore possible mechanisms behind their unusual accumulation. Eobodotria bridges a ~165 My gap in the cumacean fossil record, provides a reliable calibration point for molecular studies, and expands our understanding of exceptional preservation in past and present tropical settings.