Thursday, February 9, 2017

Trigonarca californica

This post concerns a common Late Cretaceous bivalve (clam) that lived in California approximately 92 million years ago (Turonian time). It is Trigonarca californica Packard, 1922, which is known from northern California (Siskiyou County) to southern California.

The specimens shown below are from the Santa Ana Mountains of Orange County, and they were collected from the Baker Canyon Member of the Ladd Formation. As this locale, where specimens can be abundant, this species lived in sandy, warm, shallow-marine waters. A collector recently kindly donated these specimens.

Right-hand valve of Trigonarca californcia Packard. Length 4.4 cm.

          
This unusual specimen shows the somewhat separated valves of a formerly closed-valved specimen
of Trigonarca californica Packard. The hinge with its distinctive teeth are nicely preserved. Length  of the left-hand valve (at the front of the photograph) is 4.3 cm.

The sturdy shell of this species has the shape of a rounded triangle. Its teeth (dentition) are distinctive and consist of numerous, relatively heavy, short, straight teeth along its hinge.

Genus Trigonarca, which belongs to family Glycymerididae, was widespread, with occurrences in North America, Europe, South Africa, and India. Trigonaraca is of Late Cretaceous age.

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