A clam for the ages

Venericardia is a widely distributed genus of shallow-marine bivalves (clams) in the family Carditidae. This genus was abundant during the Paleocene and Eocene epochs (a cumulative range of 66 to 34 million years ago). The highest biodiversity of Venericardia was in the Eocene. The genus needs detailed classification studies of all its various subgenera found throughout the world. Detailed studies are much needed to evaluate the likely possibly of over naming of species/subspecies found on the west coast of North America. The genus is now extinct, with the last survivors of this genus dying out apparently in the early Miocene.

Lamarck (1801) first described the genus Venericardia based on well preserved shells of this bivalve in the Paris Basin, France. The aragonite shells of this genus are commonly large and very sturdy, with wide radial ribs crossed by concentric growth lines on the exterior. The interior of the shells are characterized by long posterior teeth, much shorter anterior teeth, and two prominent elliptical-shaped muscle scars connected ventrally by a continuous line. Some species have prominent nodes along the inner margins of the shell.

These two images show the plaster replicas of the exterior and interior surfaces of a left-hand valve (6.5 cm high and 7 cm wide) of Venericardia planicosta Lamarck, 1801 from an Eocene shell bed at Grignon, Paris Basin, France. 

Venericardia (Pacificor) lutmani Turner, 1938, lower Eocene (Ypresian Stage), southwestern Oregon; plaster replicas. Left image is the exterior of a left valve, and the right image is the exterior of the right valve of a single specimen (9.25 cm high and 10 cm wide) which, upon burial, became separated from one another. 

These two images are the corresponding interior views of the same plaster replica shown immediately above.

Venericardia (Pacificor) hornii calafia Stewart, 1930, middle Eocene (Lutetian Stage), southern California. Exteriors of left-hand and corresponding right-hand valves of the same specimen (whose valves [9 cm high and 9 cm wide] are closed very tightly).

Dorsal (hinge) view of same specimen of V. (P.) h. calafia shown immediately above. Left valve is on the left side of image, and right valve is on the right side of image

Venericardia was an infaunal (burrowing) suspension feeder that lived buried just beneath the surface-water interface. Its optimum habitat was in relatively deep, shallow-marine (shelfal) environments, but its shells are commonly found as transported remains in coastal-storm beds.

Cone Shells: Past and Present

“Cones” or "cone shells" are common names for a large group of marine gastropods, whose shell is shaped like a geometric cone. Current sources say that there are between 500 and 800 species of modern cones. Their classification has been in a state of change during the last decade because of new information based on DNA studies of their soft parts.

Cone shells, which can have beautiful color patterns, have been traditionally very popular among shell collectors. If the species is rare, like the one shown below, specimens can be very expensive to purchase. Conus gloriamaris, the so-called "glory of the sea" is a prime example. About 35 years ago, it was considered to be vary rare, hence it was highly priced and worth thousands of dollars. Then many new specimens were found, and the price went way down, to hundreds of dollars.

Conus glorimaris (height 9 cm), West-Pacific region, both shallow and deep-marine depths.

Cones have their greatest diversity in the Western Indo-Pacific region, but a few species have adapted to warm-temperate (coolish) environments, like that found in southern California. Conus californicus is the only cone found today on the west coast of the United States. It is common as beach drift on southern California beaches in Ventura County. This species also has a fossil record in this same area.

Conus californicus (biggest specimen is 3 cm height, Ventura County beach drift, southern California). These shells have been smoothed somewhat by wave action during transport along a beach.

Ancestral cone shells most likely preyed on marine worms because the majority of living cones are vermivorous, that is to say, they  feed on polychaete worms or other worms. During the Miocene (about 15 to 20 million years ago), it is likely that some cones began to hunt for mollusks and fish. This resulted in an explosive adaptive radiation, with an increasing number of cones resorting to these more specialized feeding strategies. Today, there are some cone shells that have retained ancestral feeding habits by preying on worms, but these cones can resort to feeding on mollusks or on fish. One example is Conus tessulatus. It is known to be able to spray venom near the gills of fish, thereby possibly immobilizing them. This technique, however, is not always successful.

Conus tessulatus (4.5 cm height, Seychelles Island, Indian Ocean), a less-derived (in an evolutionary sense) cone. 

Modern cones have developed more effective techniques of delivering venom to their prey. One way, which is used by C. marmoreus (see photos below) is to use a hollow harpoon-shaped tooth that can be injected into a fish. As soon as the fish is paralyzed, the cone "reels" in the fish. Other cones inject extremely toxic venom, and the fish is paralyzed almost immediately.

Conus marmoreus (7.5 cm height) Indo-Pacific region. This a common cone shell, whose shell is thick and heavy. 

Cone toxins are aptly named conotoxins, which are complex cocktails of neurotoxic disulfide-rich peptides. Some of these cone toxins are lethal to humans, thus you should never handle a live cone.

Conus textile (6 cm height, Indo-Pacific region, shallow depth). This is a "deadly" cone, which injects its victims via sharp darts.

Conus geographus (height 9 cm, Indo-Pacific region, shallow water). This cone is well known for its very toxic venom, and some say it is the "number one" most toxic cone. Even predators of mollusks avoid this shell! As a result, the shell of C. geographus is light and thin, unlike nearly all other cone shells.

Cone shells have a fossil record extending back to the Eocene, about 50 million years ago. They had a cosmopolitan (globally widespread) distribution at that time, including occurrences in southern California, southwestern Oregon, and southwestern Washington. Eocene cones are smaller in shell size than most modern cones.

Conus californianus (1.7 cm height, middle Eocene Tejon Formation, southern California). The drill hole in this shell was most likely made by a boring gastropod, belonging to the noticed family.

Conus cowlitzensis (3.6 cm height, late middle Eocene Cowlitz Formation, southwestern Washington). This species is similar morphologically to C. californianus and, together, they likely form a lineage.

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.

Tejonia moragai

This post concerns the ampullinid Tejonia moragai (Stewart, 1927), a moderately common Eocene shallow-marine gastropod found from southwestern Oregon to San Diego. This gastropod is known only from upper lower to upper Eocene strata (approximately 50 to 38 million years ago).


  

Tejonia moragai is small to medium-size. The above picture on the left is the front or apertural view of an adult specimen (30.7 mm height, 22.6 mm diameter). The picture on the above right is the abapertural or back view of the same specimen.

This gastropod is characterized by having an inflated last whorl that is smoothish but with minute spiral sculpture, a somewhat moderately elevated spire with tabulate (squared-off and indented) whorls, a distinct umbilical pit, and an absence of an umbilical callus. 

If you look at my previous post, which concerns the Eocene Pachycrommium clarki, you will see that T. moragai resembles P. clarki. There are a few subtle differences, thus, in my opinion, the two gastropods are different species. Tejonia moragai is smaller in size, has minute-spiral sculpture (lines), an umbilical pit rather than a slit, and no umbilical callus. The sculpture, however, could easily be worn or weathered away, thereby making the distinction between these two species difficult. The main question, however, is whether they belong to the same genus? An answer  requires a detailed comparative study, which has so far, been wanting.

Eocene shallow-marine gastropod Eocernina hannibali (Dickerson, 1914)

This post concerns Eocernina hannibali (Dickerson, 1914), an Eocene shallow-marine gastropod (snail) commonly found in silty sandstone beds. It ranges from northwestern Washington State, coastal Oregon, all through coastal California, to the eastern Laguna San Ignacio area in Baja California Sur, Mexico. This gastropod is an index fossil (i.e., indicative of) the early and middle Eocene (approximately 55 to 40 million years ago). 

Eocernina hannibali is a medium to large-size species. The above picture on the left is the apertural or front view of an adult specimen (65 mm height, 53.1 mm width) of E. hannibali. The picture on the above right is the abapertural or back view of the same specimen. This specimen is representative of the larger individuals known for this species. Growth lines are especially apparent on the back side.

Eocernina hannibali is characterized by having a globose, smooth shell consisting a large last whorl (which contained the living animal), a rather tiny spire (or tip), and a wide smooth band (callus) adjacent to the opening (aperture) of the shell. The aperture becomes filled with sand during burial.

This picture shows the main morphologic features of the same specimen
 of E. hannibali shown above.

Locally, if the ancient environment was favorable, there will be many hundreds of specimens of this gastropod at a single locality, with sizes ranging from juveniles to late-stage adults. At these particular localities, specimens of E. hannibali are complete and so common that collecting them resembles "plucking small potatoes out of a bag." 


Dickerson originally put the species in family Naticidae and genus Natica. Recent naticids, which are diverse, are known to be carnivores that drill holes in other shells in order to reach the tissue of their prey. Modern work shows that E. hannibali belongs in family Ampullinidae, a nearly extinct family whose recent members are  herbivores that eat algae. This familial assignment is logical because E. hannibali can be extremely abundant. If it were a predatory snail, normally it would be rare to uncommon in fossil beds.

The classification of ampullinids, like many other fossil mollusks (e.g., snails and clams) is in a state of flux. To add to this confusion is that Eocernina resembles several other similar looking extinct and recent genera and species, thereby making positive generic identification a challenge. A meticulous comparative study of all these "look-alikes" is much needed.