Yaadia and Quadratotrigonia Cretaceous bivalves

This post concerns two species of "knobby" bivalves (clams) of Cretaceous age. They have medium-sized, sturdy shells with ovate or quadrate shape, and their shells are ornamented with widely spaced, oblique radial ribs bearing large nodes (knobs). Early workers referred to these kinds of bivalves as "knobby trigoniids."

 Two views (left vs. right valves) of a plaster cast of a complete specimen (length 7.4 cm = from left margin to right margin) of the "knobby trigoniid" known as Yaadia leana (Gabb), Early Cretaceous (late Albian?) from Alaska. 

Two views (left vs. right valves) of a plaster cast of a complete specimen (length 100 cm) of Quadratotrigonia mearnsi (Stoyanow), Early Cretaceous (early Albian) age, Guadalupe  Mts., southeastern corner of Arizona. This species, which also occurs nearby in Texas, differs from the preceding species by having more rows of knobs, more closely spaced rows, and a few widely spaced rows of nodes on the dorsal area, including the edge of the dorsal margin. 

Both of these knobby genera were partial burrowers, most likely with one half or less of their shell protruding into the water column. Their shells were not streamlined enough for rapid nor total burial. For a time, the sturdy and knobby shells resisted predation by gastropods and fish, which lived in the nearshore warm-temperate ocean waters preferred by this bivalve. The predation, however, became too severe (i.e., the Mesozoic Marine Revolution), and knobby trigoniids went extinct during the Maastrichtian, the last interval of the Cretaceous.

"Knobby" bivalves, in general, were very diverse during the Mesozoic. Nearly all of them went extinct at the end of the Cretaceous, most likely because of over predation by carnivorous gastropods and vertebrates (i.e., the “Mesozoic Marine Revolution.”) Today, a few relic species related to the "knobby" bivalves survive and live only in Australia. One of these species is illustrated below. 

Exterior and interior views of both valves (left on the left side, etc.) of a modern-day specimen of Neotrigonia margaritacea from southeastern Australia. Notice the "mother-of-pearl" luster on the insides of the valves. The hinge teeth of this small-sized species (2.4 cm height) are stout, long, and fit snuggly inside the sockets of the opposite valve. Neotrigonia margaritacea is a burrower but, unlike most bivalves, it can actually jump.

My post on August 19, 2017 dealt with the morphologic differences between two species of the same genus of a Cretaceous trigoniid. You can always access my previous posts by using the "Search This Blog" box in the upper right-hand side of each posting.

More information about Campanile snail

This is the second part of my post on Campanile, the genus that includes the largest snail of all time = C. giganteum.

This sketch shows the aperture of this species. The aperture is the  the shell's anterior end, where the gastropod would have been able to extend its body out into the surrounding environment. In the previous blog, the illustrated specimen of this species showed the dorsal side of the shell, and most of the aperture was missing.

Sketch of ventral side of Campanile giganteum with its aperture intact.

The specimen shown in following picture is only the upper part of a very well preserved specimen of C. giganteum from middle Eocene deposits in the Paris Basin, France. Notice that the axis (columella) of the shell bears two revolving features called folds or plaits. This type of morphologic feature is very important in the classification of gastropods.

upper part of shell of Campanile giganteum
height 22.5 cm

Fossil Campanile species have been found in Paleocene and Eocene deposits of California. The following picture is of an incomplete specimen (tip is missing) of Campanile dilloni Hanna and Hertlein, 1949 from a deposit of late Paleocene age in southern California. This species was not as large as C. giganteum. 

Campanile dilloni
height 15.5 cm

Today, Campanile is represented today by a single (relict) species, Campanile symbolicum Ireland, 1917, shown in the following picture. This snail crawls around on the seafloor in warm-shallow waters in the Perth area of southwestern Australia. This species is also known by the popular name "Bell Clapper" shell because of its overall shape. Also notice that the end of the columella (see above) is twisted and also has a narrow but distinct "spout." These features are also important in classification.

F.Y.I. The name "Campanile" is Italian, meaning "bell tower." There is tall tower, called "Campanile" on the campus of University of California, Berkeley. 

Campanile symbolicum
height 15.5 cm

LARGEST snail of all time

The fossil snail (gastropod) Campanile giganteum (Lamarck, 1804) is truly a giant among gastropods. Specimens can reach a height of 1 meter (= 100 cm = 3.28 ft = 39 in), thereby, making this species the largest snail of all time.

The specimen on the left side of the picture below pretty much represents the maximum size of this snail. The specimen is Campanile sp., cf. C. giganteum of middle Eocene age (about 45 million years ago) from the small island of St. Bartholomew in the Caribbean Sea. The letters "cf." indicate that the identification as to species is tentative because of imperfect preservation. 

100-cm high Campanile sp., cf C. giganteum (on the left)
 versus 53-cm high Syrinx aruanus (on the right);
measuring stick is 36 inches long = 91.5 cm

The picture on the left is modified from an illustration by Jung (1987, pl. 2) in the journal Ecologae geologic Helvetiae, v. 80, no. 1, pp. 889–896.

A picture of Syrinx aruanus (Linnaeus, 1758) from shallow-marine waters along the northern coast of Australia (i.e., primarily in Queensland) is included in the above picture for comparative purposes. Syrinx aruanus reportedly can reach a height of approximately 60 cm. Although the specimen shown here is only 53 cm (21 in.) in height, it is representative of a rather large-adult specimen. I have only seen a few specimens that are slightly larger. 

Campanile had wide distribution in the world during the warm times of the Paleocene and Eocene, especially from 60 to 40 million years ago. The genus became very restricted afterward because of global cooling of the oceans. In my next blog, I shall comment on some additional interesting details about this genus.