NEW EXCEPTIONALLY PRESERVED CRETACEOUS CRUSTACEAN ASSEMBLAGES FROM TROPICAL SOUTH AMERICA

Mesozoic deposits with exceptionally preserved marine crustaceans are known worldwide, but most are from modern high latitudes and only a few from tropical latitudes. Here we present several new exceptionally preserved assemblages of marine crustaceans from the Early (Valanginian, Aptian–Albian) and Late Cretaceous (Cenomanian–Turonian, Coniacian–Santonian) of Colombia, in tropical South America. These new Konservat-Lagerstätten preserve complete fossils with cuticle and soft to lightly-biomineralized tissues, including antennae, pleopods, and compound eyes. The unusual preservation of compound eyes with facets in several taxa illuminates the evolution of visual systems across decapod crustaceans, their phylogenetic significance, and the role of ecology in shaping vision. Mass accumulations of crustacean remains in these strata range from bedding planes with numerous, fully articulated juvenile and adult individuals, to surfaces with highly fragmented skeletons in close proximity. Most of these Cretaceous intervals preserve crustaceans as articulated carbonaceous remains in compact mudstones and micaceous gray claystones. Previous works have interpreted some of these deposits as ‘mass mortalities’ due to the high number of individuals preserved (hundreds to thousands). However, our preliminary studies suggest that several of these mass accumulations are partially or totally composed of articulated exuviae/molts. Massive accumulations of exuviae are common in modern oceans where large numbers of individuals gather to mate, as many species molt prior to copulation. Also, exuviae are more likely to be preserved because they have less nutrient value to scavengers, and thus less prone to biogenic reworking. Mortality and predation of recently-molted, soft-shelled individuals could account for the accumulation of some remains in other of the crustacean-rich horizons studied. Most of these assemblages seem to coincide with Cretaceous Oceanic Anoxic Events which, combined with the fossorial lifestyle of several taxa, may increase the likelihood of exceptional preservation of crustacean remains, opening new avenues for taphonomic, paleobiological, and paleoecological studies of exceptional preservation in past and present tropical settings.