GeologyRocksVentral Up Trilobite Cephalons
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A couple of field shots...
Thu, 04/07/2011 - 14:12... showing numerous partial molts on a bedding plane.
Isotelus gigas partials by solius symbiosus, on Flickr
Isotelus gigas partials by solius symbiosus, on Flickr
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Nice Trilobites! I live
Thu, 04/07/2011 - 19:19Nice Trilobites!
I live close to a place called Wenlock Edge in England, a linear feature comprising the remains of Silurian patch reefs. I keep hoping to find a good example of Calymene sp; no luck yet though, just brachipods by the arm full!
Ben.
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Paleozoic strata
Fri, 04/08/2011 - 12:48I live in the central part of a 100km dome with a slight slope of a meter or two per mile. so as one travels away from the center, progressively younger rocks are exposed.
Here is a screen grab from GeoMapApp. I live in the are that is darker pink near the center of the map(upper Middle Ordovician).
Some of the Silurian beds are very fossiliferous, as are most of the sediments of the area, but there is one bed(Brassfield Dolostone) that produces numerous Calymene celebra. Unfortunately, I don't have any photos on the hard drive.
The Mid. Ord. rocks, here, produce numerous partial Gravicalymene, then the calymene fauna abruptly changes to Flexicalymene in the early Late Odovician.
Here is a nice little Gravicalymene truncatus molt that I found under a stromotoporoid.
Gravicalymene truncatus by solius symbiosus, on Flickr
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Ventral Up Trilobite Cephalons
Submitted by solius symbiosus on Thu, 04/07/2011 - 14:06.I have been working an outcrop of early Late Ordovician limestones and shales from the central Kentucky region of the USA. A thin bed(10cm) at this outcrop is composed of, almost entirely, asaphid trilobites(Isotelus gigas) molts and orthoconic cephalopods. There are other critters too such as calymenid trilobites, rhynchonellid brachiopods, some small bivalves, ect., but it is the numerous asaphids that caught my attention.
Mostly they are molts, but occassionly, one comes across complete carapaces. While trying to chop a pygidium out of a small stone, I happen to look down and noticed this little bugger sitting at my feet... chopping on the rock had dislodge the guy from the underside of the rock.
Here is a little fellow that might have had something(cephalopod???) take a bite out its cephalon.
scale bar=2.5cm
Another molt found in the field.
scale is in cm
A curious habit of the molting process preserves some of the critters with inverted cephalons, ie, ventral up cephalon and dorsal up thorax and pygidium. When a trilobites molts, the cranial sutures spit allowing the critter to escape its carapace through the front. Sometimes, the trilobite will flip its discarded cephalon molt up-side down.
I thought that this fossil might be a complete specimen.
As I started to prep, I nearly blew through the inverted cephalon. Remember, this bed is almost entirely composed of chitinous remains.
This is one from the same bed, but about a half a kilometer from the first outcrop.
Curiously, some of the bivalves from the bed appear to still have original material in the shells... but I'll save that for another day.