RARE PULMONATE SNAILS OF EOCENE AGE, SOUTHERN CALIFORNIA

Pulmonates are nonmarine snails and slugs. Some pulmonates are terrestrial (air breathers that live on land), and some live in freshwater. Finding fossils of pulmonates in shallow-marine deposits is rare, and finding their remains in upper lower Eocene-age (40-million-years old) marine deposits is rare.

When I was a professor of geology, one of my principle-research areas was the Eocene Llajas Formation in Ventura County, southern California. After going there for many years, only two pulmonate specimens were found (both from the same locality). The best preserved one of these two specimens is illustrated below, for the first time.

I contacted a pulmonate expert, Dr. Barry Roth (recently deceased), to get his professional opinion as to whether or not these two specimens could be identified as to family/genus. After examining the specimens, he concluded that the two specimens are indeed, pulmonates, but that their preservation does not allow identification beyond the general term “pulmonates.”

Because the two specimens are so rare, I decided to mention them in my blog, in the hope that in the future, more can be deciphered about them.

Fig. 1: Apertural view, 5 whorls present, diameter 25 mm, height 17 mm. The width/height ratio is 1.47.

Fig. 2: Top view of previously shown image, 4 whorls present, diameter 21 mm, height 15 mm. The width/height ration is 1.40.

Fig. 3: Bottom view of previously shown image.

Roth (1988) discussed pulmonates from other similar geologic-age nearshore deposits in southern California. He did not mention, however, of any pulmonate snails having ever been found in the Llajas Formation. 

The depositional environment of the bed in the Llajas Formation (i.e., the “Stewart bed”) that contained the rare pulmonate specimens is shallow-marine and represents a shoreline environment, adjacent immediately adjacent to a deeper water marine environment (Squires, 2022). It seems likely that these pulmonate shells were washed “out to sea” and floated to where they eventual settled out and became incorporated in the sediment.

REFERENCES CITED

Roth, B. 1988. Camanid land snails (Gastropoda: Pulmonata) from the Eocene of southern California and their bearing on the history of the Camaenidae. Transactions of the San Diego Society of Natural History, v. 21(no. 12), pp. 203-220.

 

Squires, R.L. 2022. The earliest Ancistrolepis (Gastropoda: Buccinidae) and its geologic implications. PaleoBios 39(2):1-11, cover + figs. 1-4.