Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura)
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Abstract
The Late Jurassic marks the first major radiation among true crabs (Brachyura) in reef environments, followed by another diversification in the mid- to Late Cretaceous in multiple habitats. We studied brachyuran carapaces from Mesozoic sponge- and coralassociated limestones in Europe. Six new taxa are described: Late Jurassic Europrosopon gen. nov., Eodromites bernchrisdomiorum sp. nov., Prosopon josephcollinsi sp. nov., Tanidromites nightwishorum sp. nov., and T weinschenki sp. nov.; and midCretaceous Eodromites cristinarobinsae sp. nov. Furthermore, we recognize four junior synonyms: Eodromites grandis (=E. guenteri), Tanidromites scheffnerae (=T wysokaensis), and Europrosopon aculeatum (=E. verrucosum and E. barbulescuae). Five taxa are reassigned: Eodromites aequilatus to Tanidromites, Tanidromites rotundus to Eodromites, Nodoprosopon dzhafarberdensis to ?Abyssophthalmus, Nodoprosopon from Nodoprosopidae to Homolodromiidae, and Rathbunopon from Glaessneropsidae to Prosopidae. Several other taxa are redescribed. The latter reassignment indicates that Rathbunopon does not represent an example of extreme convergent evolution as implied previously. Conversely, the frontal structure consisting of a rostrum with two diverging spines and outer orbital spines appears a remarkable example of convergent evolution of the goniodromitid Navarradromites toward members of Homolodromiidae, for which this frontal structure is characteristic. Rostral spines represent another example of convergent evolution. Some specimens are extraordinary: A specimen of Abyssophthalmus cf. A. spinosus represents the largest complete reported Jurassic brachyuran thus far and one specimen of Planoprosopon aff. P hystricosus bears one of the largest known parasitic isopod-induced swellings (ichnotaxon Kanthyloma crusta) relative to carapace size. Overall, our results indicate that biodiversity and convergent evolution in Mesozoic brachyurans remain understudied.