41-10 Brachyuran Hunger Games: the origination and establishment of the modern crab (Brachyura) fauna during the Cenozoic

Session: Paleontology, Stratigraphy, Sediments, and Soils (Posters)

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Abstract:

Brachyuran decapod crustaceans (crabs) have a well-documented fossil record, with over 2000 species described.  Mesozoic brachyuran occurrences have been summarized in the last decade or so, with considerable attention to the podotrematous crab lineages and the victims and survivors of the end-Cretaceous mass extinction.  Paleocene crab faunas have been shown to include both Cretaceous refugees and new lineages.  Eocene and Miocene crab occurrences, however, have not yet received comprehensive attention.  The Eocene and the Miocene each yielded peaks in numbers of fossil crab genera and species across geologic time, and each can be characterized by a distinctive brachyuran fauna.

Of extant families, Eocene time was dominated by the derived, extant crab families Aethridae, Calappidae, Cancridae, Carpiliidae, Carcinidae, Hexapodidae, Majidae, Parthenopidae, Pilumnidae, Portunidae, Retroplumidae, Tumidocarcinidae, Xanthidae, and Zanthopsidae and the podotrematous Dromiacea and Raninoidea. Eight derived families originated during the Eocene but are now extinct. Thirty-five extant families originated in the Eocene.  Thus, the Eocene crab fauna can be considered the time of origination of many modern crab lineages yet remained quite distinct from the fauna seen in modern oceans.  Several families with few or no modern representatives were dominant during the Eocene.  Preliminary data suggest that Aethridae and Calappidae may have been replaced by Leucosiidae by Miocene time, as they occupy similar niches and life habits. Carpiliidae, Tumidocarcinidae, and Zanthopsidae may have been outcompeted by Pilumnidae and Xanthidae by Miocene time, as all have similar overall carapace shapes and habits.

Miocene time was a crossroads in brachyuran faunal composition.  Extant genera within Calappidae, Cancridae, Carcinidae, Epialtidae, Goneplacidae, Leucosiidae, Majidae, Pilumnidae, Portunidae, and Xanthidae dominated during Miocene time. At the same time, lineages that had been abundant and diverse during the Eocene became extinct or dwindled toward their modern low diversity. Those crab families that rose to prominence during the Miocene became the dominant families in terms of diversity in modern oceans. Most crab family extinctions occurred by the end of the Miocene, with just a few lineages becoming extinct in the Pliocene or later. Thus, with a few exceptions, the Holocene crab fauna was established by the Miocene. Renewed attention to global and local conditions that spurred the change in brachyuran fauna between the warmer Eocene and cooler Miocene might help inform modern biodiversity issues.

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

doi: 10.1130/abs/2026SE-11729

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