A reconstruction of an evolutionary scenario for the Brachyura (Decapoda) in the context of the Cretaceous-Tertiary boundary

In this article, I map the currently known brachyuran fossil record on a recent cladograrn of Brachyura, the true crabs. The hypothesis of brachyuran phylogenetic relationships is based on a cladistic analysis of brachyuran foregut characters. With this approach, the following scenario of the evolution of Brachyura is proposed. The representatives of Brachyura that occur earliest in the fossil record (Dromioidea) take the most basal position in the cladogram, followed by Homolidae. These taxa reach their highest species diversity during the Cretaceous, together with Raninidae and Cymonomidae sensu lato. The analysis reveals that the majority of the "higher" crabs (Xanthoidea, Portunidae, Cancridae, and Oxystomata sensu lato) as well as their common ancestor existed already by the end of the Cretaceous. In particular, a constant increase of brachyuran species diversity has been registered from the Eocene to the Miocene. Most taxa of the Brachyura (with the exception of the Carcineretidae) remained unaffected by the events at the Cretaceous-Tertiary-boundary. Hence, the data suggest the events at the K/T-boundary have had a weaker influence on the species diversity of the Brachyura and of the Decapoda in general, than originally presumed: i.e., there was no mass-extinction of crabs.