Excellently preserved specimens of the large rudist Macgillavryia have been described for the first time from the Campanian Samhan Formation in the vicinity of Filim and Hayy on the eastern side of the Haushi-Huqf massif in Oman. A new species, M. chubbii, was named and found to be equivalent to other species of Macgillavryia from the Caribbean domain. The exceptionally well-preserved holotype with its articulated valves allowed the reconstruction of the functional morphology of the mantle. The indications are that the left valve of M. chubbii covered only a small part of the commissural area, leaving a large part of the mantle of the right valve directly exposed to sea water and sunlight. As a result, M. chubbii has been proposed as a potential candidate for an association with zooxanthellae. Macgillavryia is a typical epifaunal rudist that probably lived in very shallow, clear seas. The shell was not buried during its lifetime but was exposed to epibionts and bioeroders. The excellent exposures allowed the reconstruction of relationships between Macgillavryia and other biotic or abiotic components. They formed a densely packed association with spaces filled by a very coarse bioclastic material. The superpositioning of two or more layers with superstratal growth fabrics created individual rudist banks more than 1 m thick covering several hundred square meters. Paleobiogeographic reconstructions have connected M. chubbii in Arabia with Macgillavryia in the Caribbean by eastward dispersion through the Pacific region.

Excellently preserved specimens of the large rudist Macgillavryia have been described for the first time from the Campanian Samhan Formation in the vicinity of Filim and Hayy on the eastern side of the Haushi-Huqf massif in Oman. A new species, M. chubbii, was named and found to be equivalent to ...