Exceptional preservation of comma shrimp from a mid-Cretaceous Lagerstätte of Colombia, and the origins of crown Cumacea

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.