The massive death of lobsters smothered within their Thalassinoides burrows: the example of the lower Barremian from Lusitanian Basin (Portugal)

Some years ago an exceptional site with the preservation of the mecochirid lobster Meyeria rapax (Harbort) within their burrows was described in the Early Cretaceous of Cabo Espichel sector, Lusitanian Basin, Portugal. The large number of articulated specimens preserved at the bottom of Thalassinoides burrow systems in, at least, four different beds of the Boca do Chapim Formation (lower Barremian) suggests that a sudden cyclic event was responsible for the collective killing below the bottom of a confined lagoon, and led to the very rare preservation of both burrows and producers. The explanation may be found in the highly heterogranular, coarse-grained clastic filling of the burrow systems which represent influxes of freshwater and large volumes of siliciclastics that may had suddenly drop the salinity of the carbonate lagoon and smothered the endobenthic communities. These climate-related events seem to have been spread in a wider region of the Lusitanian Basin during, at least, the lower Barremian, since previous findings took us to discover a new site in the correspondent Ribeira de Ilhas Formation, at Ericeira sector. In this study we also document the evolutionary trend in the occurrence of Thalassinoides associated to glyphoid lobsters since the Early Jurassic to the Aptian, and their replacement in soft substrates by thalassinideans, with few exceptions for chelate lobsters, after the Late Cretaceous. This trend to behavioral convergence of the fossorial habit matches lobster and thalassinidean diversity and evolutionary patterns through time recognized recently.