A new pseudolivine gastropod genus from the lower Tertiary of North America

Abstract

A new genus, Calorebama, is proposed for a clade of pseudolivine gastropods (family Buccinidae) that has its earliest species in the lower Paleocene (Danian) of Alabama, its next earliest species in the upper Paleocene (Thanetian) of Alabama, and its subsequent species in the Eocene of California, Oregon, and Washington. Calorebama is characterized by an inflated biconical shape, a biangulate body whorl usually with strong nodes on the shoulder, and fine to medium spiral ribbing that is coarser anterior to the medial pseudolivine groove.Previously, these pseudolivines now being placed in Calorebama were assigned to the genus Pseudoliva. Study of the literature and every available museum specimen showed Calorebama to have five species and two subspecies, all of which have biostratigraphic integrity.Calorebama unicarinata (Aldrich) is the earliest species, and it, along with C. tuberculifera (Conrad), are the only known Gulf Coast species. Calorebama dilleri dilleri (Dickerson) is the earliest representative of the genus on the West Coast of North America, and it arrived during the early Eocene (Ypresian). Probable geographic isolation of C. dilleri dilleri in central and southern California resulted in lineage splitting and the appearance of C. dilleri lineata (Gabb), which phyletically evolved into C. inornata (Dickerson). Calorebama dilleri dilleri persisted in northern California and phyletically evolved into C. dilleri kirbyi (Clark), which similarly evolved into C. volutaeformis (Gabb).Calorebama inornata and C. volutaeformis, the youngest species of the genus, became widely distributed along the West Coast of North America before becoming extinct by the end of the earliest late Eocene.

Family Pseudolividae (Caenogastropoda, Muricoidea): A polyphyletic taxon*

“…The taxon Pseudolividae Fisher, 1884, had been previously used by several researchers {e.g., Cossmann 1901, Golikov and Starobogatov 1975, Squires 1989), but it was better defined as a family by Kantor (1991), based on anatomical features of basal neogastropods. The family reunites genera previously considered as belonging to several other families, including, e.g., Cancellariidae {Bentlwbia Dali, 1889), Buccinidae {Buccinorbis Conrad, 1865), and Olividae (Melapiwn Adams and Adams, 1853;PseudoUva Swainson, 1840;Sylvnnocochlis Melvill, 1903;Zemira Adams and Adams, 1853).…”

Popenoeum, a new pseudolivine gastropod genus: widespread and most diversified during the Paleocene

“…Pseudoliva Swainson, 1840, is the name given to nearly all fossil and Recent forms of pseudolivines. A spec imen of the type species, P. plumbea (Dillwyn, 1817, p. 617), is illustrated in Squires (1989). Popenoeum n. gen. differs from Pseudoliva in the following features: higher spire; tabulate whorls; prominent subsutural canal; swollen collabral costae that pro duce tubercles along the body whorl shoulder; closely spaced fine to strong spiral cords; and pseudolivine groove more pos teriorly located on the body whorl.…”

“…4, 9). Pegocomptus howardi is known from upper Paleocene (Thanetian) strata in southern California (Dickerson, 1914;Zinsmeister, 1983aZinsmeister, , 1983b Squires, 1989, is the name given to two Paleocene species of pseudolivines from Alabama and to all the Eocene pseudolivines from California, Oregon, and Washington. Popenoeum n. gen. differs from Calorebama in the following features: subsutural canal; collabral costae; coarser spiral cords; and an absence of a subsutural swollen area with a concave ramp area.…”

“…Discussion. -The classification of pseudolivines is discussed in Squires (1989). Pseudoliva Swainson, 1840, is the name given to nearly all fossil and Recent forms of pseudolivines.…”