The eyes are the only thing that is damaged on the above specimen and is typical of most fossils I find of this genera. It may be because the eyes were raised up off the cephalon enough such that they more easily break off while being extracted. Isolated pieces from molts are common just like many other genera of Trilobites. Below is a small cephalon.
This is a Pygidium (tail) from a larger specimen.
The stippling pattern that you see on the larger specimens is very common but I don't believe is related to any exterior decoration. Rather it seems to be more of an internal feature, perhaps connection points for muscles. A couple of views of some larger Cephalons (heads). Notice the small scoop that is on the very tip of the Cephalon in the first two pictures. Maybe they used this to help burrow or dig for food.
I told you that this genera got big. Below are pictures of a huge 8" long specimen that is missing it's head (and the tail is chipped). It looks like the head might have been pointed down into the rock as if trying to enroll but, once I extracted the specimen, I found no evidence of any shell beyond what was already exposed. So this is likely another molt.
Typically I find Dipleura fossils in areas of the Mahantango formation that were very muddy and are now siltstone and mudstone. In areas of the formation that are sandier you more commonly find Greenops and Phacops. To me this indicates that Dipleura preferred soft, muddy sediments that had calmer waters father away from fast currents.
I found two more specimens over the July 4th weekend. The first is a prone example which I think is a molt as the cephalon seems to be a little askew. You can see there is some matrix still attached on the sides. The specimen is a little delicate right now and I'm worried about breaking it if I try to remove excess rock.
At the same site I found the above specimen, comes this enrolled Dipleura. It's smaller than the other one and is about 1.5" in diameter.
Dave those are very cool trilobites! You say that it is one of the commonly found species (Greenops and Phacops being the other two). So what are the other species that occur in the Mahantango? And will you be showing us some of them in future posts?
ReplyDeleteDan
Dan,
ReplyDeleteI wish I could but Phacops, Greenops and Dipluera are the only Trilobites I've found in the Mahantango. Trilobite diversity started to decline in the Early Devonian and was severely hampered during extinctions in the middle Devonian (the Kacák and Taghanic events) and Late Devonian (the Frasnian-Famennian Kellwasser event). Another possible reason for only three genera is the paleoenvironment which was a river delta similar to the Amazon or Nile river deltas.
Hello Dave,
ReplyDeleteFirst of all I would like to thank you for taking the time to share this wonderful material.
I recently acquired a dechenella which I believe is from your neck of the woods. It came from a old collection and was from Pa. Do you ever run across any dechenella parts in your travels? If so, what kind/s? I'd love to share a pic.
--Steve
Steve,
DeleteThus far I have not found any Dechenella trilobites here in Pennsylvania. I know they exist but collecting sites are few and far between these days. Much of what is in old collections came from sites that are now gone or too overgrown to collect at.
-Dave
I think that that huge trimerus dekayi isn't a molt, but rather an example where a predator has attacked it or the head was dissolved.
ReplyDeleteI have finally found a reasonably complete trilobite that's a Trimerus dekayi! It's enrolled with the thorax and either the cephalon or the pygidium, I can't tell.
ReplyDelete