DECAPOD POPULATION PALEOBIOLOGY AND PALEOECOLOGY OF THE LATE CRETACEOUS MISSISSIPPI EMBAYMENT, USA

A diverse assemblage of decapod crustaceans from the well-known Blue Springs Locality of the Maastrichtian Coon Creek Formation in Mississippi yields a detailed picture of ancient decapod ecology. Bishop (1983) originally described ten decapod species based on about 1300 specimens; Kornecki (2017) updated the decapod fauna. We examined nearly 1500 specimens of decapod crustacean fossils collected over four days. Several hundred specimens originally identified as species of Tetracarcinus, Dakoticancer, and Seorsus (all Dakoticancroidea) are shown to be conspecific, documenting growth stages, sexual dimorphs, and intraspecific variation in the dorsal carapace and sternum. Allometry and development of carapace keels and regions are evident in smaller versus larger specimens. Dakoticancroid crabs account for nearly 60% of all collected decapod specimens. Although dakoticancroid crabs are extinct, large, extant, benthic brachyurans are typically predators and scavengers with a wide range of food preferences. The second most common decapod collected at Blue Springs was Mesostylus, a type of “callianassid” shrimp that inhabited intricate burrow systems in shallow marine regions. Co-occurring large, benthic lobster-like forms, Linuparus and Hoploparia, may have been nocturnal predators, were omnivorous, and preyed upon or scavenged on other crustaceans, mollusks, and bivalves. The raninoidan crabs Cretacoranina and Bournelyreidus survived by shallow burrowing, possibly as ambush predators. Rare elements of the decapod fauna include the brachyuran Cristipluma, and some taxa previously reported were not found in our collection. The decapods themselves were likely prey for fish, shell-crushing sharks, and ammonites, and probably even mosasaurs, plesiosaurs, and birds such as Hesperornis. Because the decapod specimens were mostly collected as float near the bottom of a 15 meter slope, occurrence by individual layers is unknown except for very large specimens of Tetracarcinus in a single layer near the top of the section. Thus, it is possible that juvenile and adult Tetracarcinus as well as other decapods exhibited habitat partitioning, but layer by layer collecting will be necessary to test this.