History of reef-dwelling Decapod Crustaceans from the Palaeocene to the Miocene with comments about Mesozoic occurrences

The evolutionary history of decapod crustaceans living on reefs and other marine organic build­ ups is followed from the Palaeocene to the Late Miocene, with comments about similar Mesozoic 1 Magyar Állami Földtani Intézet, H-1143 Budapest, Stefánia út 14. 238 Földtani Közlöny 134/2 occurrences. Crabs live on modern reefs in a great diversity. Their fossil counterparts also show a diversity higher than that which lived on other habitats, although data are not very numerous and scattered in time, in geographic position and in palaeolatitude. Changes in the taxonomic composition are explored. Due to the scarcity of data no clear picture emerges but the proportion of primitive crabs (Dromioidea, in terms of number of recorded species) seems to decrease, while more advanced forms, among others the Xanthoidea seem to gain in number. The apparent diversity is highly dependent on the extent of our knowledge, but a relatively low diversity seems to occur in the Palaeocene, a much higher one in the Eocene. The known Miocene faunas mostly represent a quite high palaeolatitude (Hungary and surrounding countries), with moderate diversity, but one from southern Japan represent a more southern setting. A more or less clear change in carapace form can be observed in the families Porcellanidae and Xanthidae: the carapace growth wider with the geological time.