The trace fossil record of burrowing decapod crustaceans: evaluating evolutionary radiations and behavioural convergence

Trace fossils assigned to the activity of decapod crustaceans are well known from the stratigraphic record. Changes in abundance and ichnodiversity of these structures through the Phanerozoic have been analysed. A database summarising trace fossil occurrences was compiled. This information is interpreted with respect to the life history of burrowing decapods, as inferred from the body fossil record. The Palaeozoic records are sparse and difficult to interpret in terms of producers. The presence of burrow systems (i.e. Thalassinoides) in Early Palaeozoic rocks most probably records burrowing by groups other than decapod crustaceans, therefore reflecting behavioural convergence. The possibility that decapods may have produced burrow systems in the Late Palaeozoic cannot be ruled out completely, but it is more likely that other malacostracans were involved in the construction of these structures. Post-Palaeozoic records are more confidently attributed to decapods and the slow rise in the abundance of these structures through the Mesozoic shows a good correlation with the trends recorded in the body fossil record. During the Palaeogene, the number of decapod ichnofossils reported is considerably lower than that for the Cretaceous. This may reflect the effect of the end-Cretaceous mass extinction and/or monographic effects related to the larger amounts of ichnological work carried out on Cretaceous shallow-marine deposits. During the Neogene, the abundance of decapod trace fossils underwent a remarkable increase, and crustacean burrows became dominant elements of the shallow-marine ichnofaunas, commonly a part of communities displaying complex endobenthic tiering patterns. Finally, the data are related to the history of infaunalisation. In the colonisation of infaunal ecospace, decapods played an important role, becoming dominant components of the modern faunas.