Cretaceous clam chowder: The first evidence of inquilinism between extinct shrimps and bivalves

Records of extinct organisms interacting with each other are limited primarily to evidence of predation and records of parasitism. However, in rare cases, records of organisms living within another one (inquilinism) have been identified. To expand the rather limited record of documented euarthropod inquilinism, we present a new example of three articulated swimming shrimps within an inoceramid bivalve from the Cretaceous (Albian) Allaru Mudstone, Queensland, Australia. We suggest that the specimen represents the first record of decapod inquilinism from Australia and the first record of extinct shrimps within a bivalve. We also show an inoceramid from the same area and age containing at least 30 fish, a specimen that supports the inquilinism hypothesis. Further examination of these rare specimens is a cardinal direction to better understand how extinct crustaceans interacted with other organisms and to document where and when inquilinism evolved across the Phanerozoic.