70-6 Decapod Body Size Remains Remarkably Stable Throughout Evolutionary History

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns (Posters)

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Abstract:

Decapod crustaceans have played essential roles in aquatic habitats since their Devonian origins, especially since the onset of the "Mesozoic marine revolution." However, their trend in body size is understudied. Here, we use maximum likelihood methods to document and analyze this trend, using a comprehensive database of decapod genus body sizes. The order-wide trend has been remarkably stable, on average, throughout their history, in spite of major increases in diversity during the Mesozoic and Cenozoic. A statistical model of stasis is best supported by the data, although an unbiased random walk cannot be ruled out. The range of maximum and minimum size expands with increasing diversity, consistent with a lack of directional size change. Some major decapod groups do appear to increase body size, with the earliest members of some clades originating at smaller body sizes, especially among brachyuran crabs and perhaps caridean shrimps and polychelidan lobsters. Anomuran hermit crabs and caridean shrimps include the smallest decapods, on average, while achelate and polychelidan lobsters include the largest ones. Sample sizes are low for non-marine (terrestrial and freshwater) genera in our database, but we find no significant differences in body size for decapods inhabiting these environments. Although Paleozoic decapods are too rare to include in statistical analysis, the fact that Devonian and Permian decapods were approximately the same size as post-Paleozoic genera also suggests decapod body size has not changed significantly. These patterns suggest decapod body size has remained remarkably unchanged throughout their evolutionary history.

The first two authors contributed equally. This research has been supported by NSF grant #2322080.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8126

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