Taphonomy of decapod crustacean cuticle and its effect on the appearance as exemplified by new and known taxa from the Cretaceous–Danian crab Caloxanthus

• Two new species of the crab Caloxanthus are described; one is redescribed.
• Caloxanthus lived in a variety of sedimentary environments.
• Presence or absence of cuticle can influence the decapod's appearance dramatically.
• This phenomenon is known, but is insufficiently addressed for new taxa in 2013.
• Whitening of specimens to enhance contrast may also obscure diagnostic features.

Decapod crustaceans inhabited a variety of environments during the Cretacous. The crab Caloxanthus is an example of this environmental differentiation as the Cretaceous–Danian species lived in siliciclastic and carbonate habitats. Here, two new species of Caloxanthus are described from different sedimentary settings: 1) Caloxanthus thompsonorum sp. nov. from the Upper Cretaceous (Santonian) of Austria found in siliciclastic sediments, and 2) Caloxanthus vignyensis sp. nov. from the Paleocene (Danian) of France found in a limestone. After examination of the marly rock containing the holotype of C. wrighti (Santonian, France), another conspecific carapace specimen was discovered; both specimens are illustrated. Caloxanthus is a prime example of how the appearance of decapod carapaces can differ among conspecific specimens with the cuticle preserved and those lacking it (internal molds). This phenomenon is also found in other decapod taxa as illustrated herein (Daira speciosa, Panopeus wronai and Chlorodiella mediterranea) and affects carapaces and chelae. Importantly, although this is known among paleontologists, in only about half (50/108, 46%) of the in 2013 newly described fossil decapod species it could be deduced with certainty whether or not a cuticle was present. Even more surprising, in only 27% of the cases the presence or absence of the cuticle was specifically mentioned. It is recommended to state whether or not the cuticle is preserved in the species description to reduce the potential of misidentification of taxa and erecting erroneous taxa. We also show that whitening of specimens to increase contrast may also obscure features on the carapace of C. wrighti. This study highlights the effect that taphonomy can have on taxonomy.

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