23-14 A Plethora of Raninids: Potential for Population Paleoecology in Decapod Crustaceans

Session: Paleontology of North America (Posters)

Presenting Author:

Authors:

Abstract:

A substantial population size is crucial for conducting population ecology studies. Such studies are rarely possible in decapod paleoecology, with only a few dozen specimens per species at most available. Usually, too few specimens have been preserved and uncovered for full population ecology studies to be conducted. Over two hundred specimens of Macroacaena schencki [Crustacea, Brachyura, Raninoida] are available in the USNM Smithsonian Collections. This species of raninid is a back-burrowing crab characterized by elongate carapaces and limbs. Specimens are found in the Keasey Formation of Northwest Oregon: an upper Eocene to lower Oligocene tuffaceous siltstone. Other decapod genera present in this formation include Megokkos, Branchioplax, and Pulalius. Through this research, we propose to determine the fossilization conditions that yielded higher quantities of specimen preservation, establish paleoecological data based on a large population size to be extrapolated to other decapod taxa, and apply our findings to modern raninids and implications for their survival in the present day.  We will investigate the preservation of these specimens to determine potential reasons as to why there are more of them preserved than other decapod species in the same formation.  

We tested three hypotheses: 1) preservation is determined by individual size and age, 2) preservation is determined by the chemistry of the surrounding matrix, and 3) preservation is determined by the back-burrowing habits of the species. To test these hypotheses, thin sections and chemical analysis, as well as individual measurements were made. Preliminary results indicate that a carapace width greater than 16.2 mm contributes to preservation. Specimen size ratios indicate that the population consists of adult crabs ranging in age from young to mature. 

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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