Minute fossils of the gastropod genus Caecum Fleming, 1813, family Caecidae Gray, 1850, are present in early Eocene rocks of the Crescent Formation and the latest Eocene or earliest Oligocene Gries Ranch Formation in western Washington State. Caecum benhami, new species, and another unidentified species were found in the Crescent Formation, and C. bensoni, new species, was found in the Gries Ranch Formation. These are the first Paleogene records of the family Caecidae from the northeastern Pacific Ocean, and among the few Paleogene records worldwide. The fossils from the Crescent Formation in Washington State are 50 to 55.6 million years in age (Ypresian) and are the earliest known record for the genus Caecum and the subfamily Caecinae Gray, 1850. The Crescent Formation fossils are also as old, or even older, than the previous oldest known record for the family Caecidae from 50 to 52 Ma rocks in New Zealand. These fossils demonstrate that the family Caecidae had diversified into at least two subfamilies (Caecinae and Strebloceratinae Bandel, 1996) and inhabited both the north and south sides of the Pacific Ocean by early Eocene time.
Gries Ranch Formation