Trilobite Molts-Up Is Down, And Down Is Up

A while back, Chris over at Ediacaran put up a post in his “Paleoporn” series describing the environment and sedimentology of two sites, in the same formation, where the same Cambrian trilobite is found. His post is a description of the orientation of the molts in the two different environments. In the comments, we discussed the curious habit of finding inverted cephalons, ie, ventral up cephalons while the rest of the critter is found in its normal position(dorsal up).

In a thin bed of the Clays Ferry Formation in Anderson Co. Kentucky, I find numerous partial molts from the trilobite Isotelus gigas. Some of the bedding planes are almost entirely composed thoracic segments, cephalons and cranidiums, and pygidiums from this large asasphid. Occasionally, one comes across the curious preservation described above.

During ecdysis, the cephalic sutures of the trilobites rupture allowing the critter to escape from the front of its carapace. Sometimes during the egress, the critter will push the cephalon upside down. Hence, what we have here.

When I found this one, it didn’t appear that much was there.

But, I brought home anyway. While hitting it with a scribe, I noticed the ventral, but I thought that it was trash and nearly blew through it… as more became apparent, I slowed up a bit(word to the wise).

I have found several more from the same locality, but those are all that I have photographed. However, here is a nice juvenile that appears to have had a bite taken out it.

More on that later.

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6 Responses to “Trilobite Molts-Up Is Down, And Down Is Up”

  1. lendail.ru Says:

    Интересно, где Вы нашли столь полезную информацию. Буду признателен если дадите истинный источник

  2. s-postal.ru Says:

    Написано конечно всё правильно, хотя и только поверхностно. В любом случае спасибо

  3. Kentuckiana Mike Says:

    Nice post.

    I am interested in reading more about your interpretation of the enrolled Isotelus that has a possible bite mark. What kind of predator would make an indentation like that?

    There are an interesting set of videos on YouTube of a presentation called Predators of the Paleozoic by Dr. Carl Brett given at the Cincinnati Geofair 2010: http://www.youtube.com/watch?v=YldqSyhFlUY

  4. Isotelus Molts « Iapetus Adventures Says:

    […] that is in the same bed, and close to, another outcrop that I have collected extensively(see here, here, and here), I came across some curious molts of an Isotelus […]

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