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Split Pea Crab Fossil P. montereyensis - California

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Split Pea Crab Fossil P. montereyensis - California

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Pinnixa montereyensis (Rathbun, 1932)

Monterey Shale
San Luis Obispo county, California, USA

Miocene Period (8 Million Years Old)

Crab : 1.06 x 0.46 inches
Matrix : 2.32 x 2.13 inches

1 inch = 2.54 cm

A nice pea crab we collected, then prepared in order to expose the claws and as many legs as possible!

Included are both sides of the split shale, positive and negative.

P. montereyensis is known for a very large body form and longer legs than the other two Pinnixa type crabs found in the locality.


Discovered along California's central coast, these crabs are found in the abundant shale south of Monterey Bay, the Monterey Shale. In a very specific layer, dating to 8 million years ago, we find primarily pea crab fossils preserved in incredible detail in the shale. Typical of a tropical coastal environment, these pea crabs are also found among the remains of fish, pine needles and cones, palm fronds, and a few other species of crabs.

This specific site in San Luis Obispo county was found by a friend of ours in late 2013, relatively still a new site, we have only been collecting here since early the following year. Different than the known site in Carmel Valley, the shale is more silicious - banded with dense chert and petroleum rich shale, adding the needed minerals for the rich iron oxidation evident on many of the fossil crab carapaces in a vivid array of colors from deep reds, black, white, orange, and yellow, what is even more unique is that this preservation is found in other localities in the region as well. Another feature is that more of a variety of crabs are found at this site, two other species of crabs Parapinnixa miocenica and Pinnixa montereyensis, as opposed to the sites in Carmel Valley.

The genus of pea crabs, Pinnixa, still live today and even along the California Coastline, from Baja to the Pacific Northwest these crabs are abundant in the Western Pacific.