The marine gastropod Fusitriton oregonensis: An interesting species today and in the past

Fusitriton oregonensis (Redfield, 1848) belongs to family Ranellidae (the so-called "tritons"). This species lives today most commonly in cool and relatively deep waters from the Bering Sea to northern California. It has been reported in Japan, and it has been reported (mostly as a fossil) in southern California. It is the state seashell of Oregon. The floating larvae of F. oregonensis can last for an extraordinarily long time (up to 4.5 years), and this would explain why it can be found in Japan today. 

This species has a medium-size shell (4 to 5 inches in length) with an overall fusiform shape. Its six convex whorls have 16 to 18 axial ribs nodulated by the crossing of weaker spiral ribs. There is a single parietal tooth near the top of the aperture.

The picture above is an apertural view of a modern specimen 87.7 mm height (3.5 inches) from beach drift at Friday Harbor, San Juan Islands, Washington. If you have ever visited the area, you will known that the ocean water there is cold enough to discourage a normal person, without a thick wetsuit, from swimming in it. The holes you see in the shell are the result of exposure to erosion while the shell was on the beach. At Friday Harbor, this species is intertidal. Southward, it lives in deeper waters (up to several hundred meters).

Abapertural view of same modern specimen.

The fossil record of F. oregonensis is from approximately middle Pliocene (approximately four million years ago) to recent.

The two pictures shown below are of a fossil specimen 55.5 mm height (2.2 inches) of late Pleistocene age (30,000 to 50,000 years old) from a marine terrace at a beach cliff near Santa Barbara. The shells in this marine-terrace deposit lived during the Wisconsin Glacial Stage, which was the fourth and last stage of the great Pleistocene Ice Age. Based on a comparison with modern bathymetric, temperature, and geographic ranges, the shells indicate a maximum water depth of 10 m and a temperature range from 11 to 20 degrees Celsius (cool temperate). This would have been cooler than the sea temperature off Santa Barbara today but similar to that off the northern California coast today. 

Apertural view of a fossil specimen missing its upper part.

Abapertural view of fossil specimen.

Mystery sand spheres

A fellow geologist recently sent me the following pictures and information about "sand spheres" he found in the general area of the shoreline region of the late Pleistocene Lake Manix, in the Mojave Desert, between Barstow and Baker, southern California. Lake Manix formed by overflow of the Mojave River between 500,000 and 25,000 years ago.

The spheres are all of small size and range from 0.51 to 1.5 cm in diameter (e.g., they are about the size of a U.S. dime). They consist of friable (= fragments come loose from the spheres when rubbed) and angular, coarse-grained material called grus, which results from the granular disintegration (weathering) of granite in an arid climate. The material making up the spheres is slightly cemented by calcium carbonate. 

The above picture is a cross-section of a sliced sphere. Compared to armored mud balls, the "sand spheres" do not have a mud core and are too uniformly of small size. Armored mud balls form when a clump of gooey mud begins to roll around under a flow of water and fragments of rock adhere to the mud surface.

The "sand spheres" shown above, in the background, might have formed in place. The "loose" ones in the foreground are derived from this more concentrated mass of them.

If you "lean in" on this far-away shot, you can make out how numerous the small spheres are (thousands and thousands) among the much larger fragments of angular rock. The "sand spheres" litter the ground sort of like rabbit or deer droppings. 

The "sand spheres" are at an elevation of 563 m, which is slightly above the Pleistocene shoreline, thus they were most likely not formed by a shoreline process. There has not been any lake water at this elevation in 18,000 years. The "sand spheres" look fairly fresh. They are on the surface and although they are not very delicate, thus it is doubtful that they have been around since the Pleistocene. My colleague believes that they might be a product of a local (recent?) downpour. 

Although the nonmarine "sand spheres" of Lake Manix resemble "sand balls" created by small "bubbler" crabs on modern beaches in the tropical ocean waters of the Indo-Pacific, they cannot share the same origin. By the way, if you have the interest you will be amazed and amused by a BBC Blue Planet video (online) that shows how these crabs form the "sand balls."

In closing, we do not know the origin of these Lake Manix spheres and could not find anything in the literature about them. Determining how they formed would be a worthy project.