Polymorphy and extinction of the Late Cretaceous burrowing shrimp Protocallianassa faujasi and first record of the genera Corallianassa and Calliax (Crustacea, Decapoda, Thalassinoidca) from the Cretaceous

A biometric study of chelae of the burrowing shrimp Protocallianassa faujasi (Desmarest, 1822), from the late Maastrichtian of the Maastrichtian type area, The Netherlands, has revealed three morphotypes. These types are interpreted as sexual dimorphs (male and female) and earliest ecdysis stages (immature male). Among the studied material are fifteen specimens of a new Cretaceous callianassid, Corallianassa acucurvata new species, one specimen provisionally assigned to the genus Calliax and a callianassid from the Danian. Burrows preserving callianassid chelae in situ are discussed. Based on burrow morphology a suspension feeding mode of life for P. faujasi is inferred, whereas C. acucurvata n. sp. probably was an active omnivorous analogue of its closest Recent relatives. The extinction of P. faujasi in the Meerssen Member appears to correspond to the increase in seagrass vegetation. The Protocallianassa-Corallianassa faunal changeover took place about 100,000 yrs before the K/T boundary in this region