PTERIOMORPHIA BEURLEN, 1944

Hickman, Carole S., 2023, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs, PaleoBios 40 (5), pp. 1-51 : 3-4

PTERIOMORPHIA BEURLEN, 1944

Five major groups of bivalves in the Keasey Formation ( Mytilida , Arcida, Pteriida , Pectinida and Limida ) are represented by taxa whose living species fall within a well-supported pteriomorph clade. Despite increasing support for monophyly from molecular data (e.g., González et al. 2015, Lemer et al. 2016, 2019), these groups encompass major radiations of extinct families and genera. Any phylogenetic perspective based on living species is seriously limited and temporally shallow. At the same time pleasing topologies based on limited sampling of living taxa leave internal relationships in the five major groups highly unresolved, but with considerable promise for increasing use of shell microstructure in phylogenetic studies. The following taxonomic treatments emphasize geological, paleoecological, paleoenvironmental, and paleogeographic insights on pteriomorph history.

All five of the Keasey major pteriomorph groups have Paleozoic origins, with arcoids and pterioids appearing in the Ordovician and mytiloids, pectinoids and limoids dating from the Devonian or Carboniferous. Extinct family-groups and genus-groups must be included in evolutionary history along with studies of historical ecology and biogeography. As noted above, the Keasey pteriomorphs provide a remarkable window on history because they occur in deep water mudstone and siltstone lithofacies during the doubthouse interval of major global climate cooling as well as an interval coinciding with tectonic change and onset of arc volcanism and large volumes of tuffaceous sedimentary input on the Pacific Northwest margin. They thrived in environmentally challenging hydrocarbon seep and peri-seep environments.

They experienced the same dysoxic and geochemically toxic conditions previously noted for Keasey heteroconch and anomalodesmatan bivalves ( Hickman 2014, 2015).

Stratigraphic range —Ordovician–Holocene.