THE MARINE GASTROPOD GENERA PERRISITYS STEWART, 1927 AND BRUCLARKIA TRASK IN STEWART, 1926: A NEW INTERPRETATION OF SHARED ANCESTRY AND ITS IMPLICATIONS FOR CRETACEOUS AND CENOZOIC TAXA

The gastropod genus Perrisitys Stewart, 1927 spans the Cretaceous-Paleogene boundary, appears to be endemic to the Northeast Pacific Subprovince (Alaska to Baja California, Mexico), and is of uncertain systematic position. The cause of its extinction early in the Cenozoic is unknown. Here, the possibility is explored that Bruclarkia Trask in Stewart, 1926, a fossil buccinid or buccinoidean gastropod genus with species found in California and the Pacific Northwest from the Eocene–Miocene, is the continuing lineage of Perrisitys; making these genera one and the same. Bruclarkia, as described, first appears as B. vokesi in the Eocene “turnover fauna” of Hickman in the Pacific Northwest. During the Oligocene and Miocene, B. acuminata, B. gravida, and B. oregonensis are the most geographically widespread members of the genus, spanning much of the Northeast Pacific Subprovince. By the middle Miocene all species in the genus are extinct. Based on morphology of shells’ penultimate whorl, sutural collar, parietal lip, and body whorl, members of the genus Perrisitys are shown to be remarkably similar to species of Bruclarkia. These similarities are discussed, as are interpretations of the lineage’s systematic placement, and implications of their shared ancestry for evolution and paleobiogeography.