Tuesday, January 6, 2015

Triarthrus eatoni trilobites from the Utica shale

Following up on my previous post, these are Triarthrus eatoni trilobites from the Utica shale near Little Falls, NY, (Ordovician, Darriwillian stage). These are frequently found disarticulated and thus are most likely molts rather than post mortem burials.

Molt with the cranidium separated from the rest of the body. Note the free cheeks still in place beneath the "floating" cranidium.

This specimen is missing the free cheeks or librigena.

Both of the above specimens were purchased at my local club show and have since been traded away to my friend Gery in France. I made my first ever visit to the site this past summer with a group of friends from the Fossil Forum. While I did not find any complete specimens, I did find quite a bit of material.

The loose cranidiums were likely the most common fossils found.

You could also find lots of mostly articulated specimens that were missing just their cranidiums. To me this indicates that the trilobites molted by splitting their exoskeleton along the seams of the cranidium and then crawled out. 

Sometimes you just found the free cheeks as pairs or singles.

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