Venericardia imbricata

Overview

Venericardia imbricata was an Eocene bivalve with a rounded shell bearing scaly ribs. It was a clam relative with two valves. Close inspection of its surface ornament tells more stories than the rounded outline alone.^[1][2]

Key facts

The ribs on the shell are not simple lines. Scaly ornament runs along closely spaced radial ribs. Comparing whether rib tops are flat or slightly convex helps distinguish apparently similar bivalves.^[1]

Time and place

It is known from middle Eocene Lutetian material, around 48–41 million years ago. Specimens from the Paris Basin in present-day France were used for comparisons. Ancient European shells also serve as a reference in studies of distant New Zealand bivalves.^[1]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The valves are broadly rounded with closely spaced radial ribs. A small area around the shell apex is concealed by the upper region. External ornament and internal structures joining the valves provide different comparative material.^[1][2]

A description of the genus Venericardia based on Paris Basin specimens of its type species imbricata gives shell heights of 25–40 mm. Width is slightly greater than height, and deep tooth-like crenulations line the inside of the shell margin.^[7]

Habitat and reproduction

Preserved shells provide the first clues to the seas inhabited by ancient bivalves. The convex body, hinge, and surface ribs can be compared alongside other bivalves. Even animals in similar environments differed in how they formed their shells.^[2][1]

Fossil discovery

A 1969 study reviewing ancient New Zealand mollusks described this species’ features as a comparative reference. It also presented the exterior and interior of a left valve separately. Fossils from distant regions met within one study.^[1]

References

1. Maxwell1969 — Middle Tertiary Mollusca from North Otago and South Canterbury
2. Treatise — Shell features of Venericardia
3. de Winter et al. (2020), “The Giant Marine Gastropod Campanile giganteum (Lamarck, 1804) as a High-Resolution Archive of Seasonality in the Eocene Greenhouse World.”
4. VUB — Giant sea snail fossil reveals climate of French Champagne region
5. Maxwell1969 — Middle Tertiary Mollusca from North Otago and South Canterbury
6. Treatise — Shell features of Venericardia
7. Gardner & Bowles (1939), The Venericardia planicosta group in the Gulf province, USGS Professional Paper189-F

Research questions

Do external ornament and the internal hinge indicate the same relationships? Bivalve research compares both to examine differences between genera and species. Even familiar names require renewed reading of actual shell structures.^[1][2]

Observation

After viewing the rounded outline, examine the scaly ribs running from the apex toward the margin. Consider the different clues conveyed by the outside and inside of the shell.^[1]