CUSPIDARIIDAE Dall, 1886

Carole, Hickman, S. & Ca, 2014, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, part IV: The anomalodesmatans, PaleoBios 31 (3), pp. 1-21 : 12

CUSPIDARIIDAE Dall, 1886

Living cuspidariids are most diverse, abundant and well-documented in the deep sea, especially at abyssal and hadal depths ( Knudsen 1970, 1979). Their origins and relationships are unresolved. The oldest records of rostrate bivalves assigned to Cuspidariidae place the origins of the family in shallow, brackish water in the Triassic (Ladinian) ( Morris 1967, Sepkoski 1992). However, re-examination of shell morphology and microstructure shows that the early Mesozoic forms are actually corbulids (myoid heterodonts) ( Harper et al. 2002) and that fossil rostrate taxa must be treated with caution. The earliest unequivocal evidence of cuspidariid shell musculature is in the Late Cretaceous (Maastrichtian) ( Runnegar 1974 text-fig. 9, p. 924).

Cuspidariid features of greatest interest to biologists are the absence of gills, the unique muscular septum, adaptations for prey capture, and modifications of the digestive system for carnivory ( Yonge 1928, Bernard 1974, Knudsen 1979, Alan and Morgan 1981, Reid and Reid 1974, Reid 1977, Morton 1987). The family has a cosmopolitan distribution, although it is especially well documented from high latitudes in the southern hemisphere ( Prezant 1998, Marshall 2002).

Fossil cuspidariids are rare in Cenozoic faunas of the northeastern Pacific and have a peculiar taxonomic and stratigraphic distribution. Ten species, including the new Keasey species, are all in the genus Cardiomya A. Adams, 1864 and all occur in rocks of middle and late Eocene age. Eighteen species in eight genera are reported in the living northeastern Pacific fauna ( Coan et al. 2000). Restriction of many of the living species to abyssal and hadal depths places them out of the normal preserved record of bathyal and shallower marine sedimentary settings. However, the absence from Neogene strata in the northeastern Pacific is puzzling.

The lack of an onshore fossil record of most of cuspidariid diversity is consistent with the hypothesis that this group has undergone a major evolutionary radiation in the deep sea and is not derived by onshore-offshore migration over geologic time of a shallow-water evolutionary radiation. However, shallow-water cuspidariids are reported from Upper Cretaceous and Eocene faunas in Texas ( Garvie 2013), and incursions of the group into shallower settings also occur in the modern fauna of the Panamic Province ( Coan and Valentich-Scott 2012).

Stratigraphic range —Upper Cretaceous to Holocene.