Spent four hours yesterday at my Bois Blanc location specifically targeting Terataspis. Overall, it was a great day for it -- sunny and warm. In fact, it was the first time this season that I've had to strip down in the field as I was actually sweating, and now bringing water to digs is essential. That weighs one down, but dehydration can impair a good dig.
Let's kick it off with Deb's lovely find. A lot of it is still buried in matrix. The telltale small, rough tubercles are present, which says Terataspis.
A field shot. Likely a portion of the pygidium, thoroughly eroded. The character of these rocks make it a challenge to find nice pieces if one were to rely solely on just surface collecting. The real trick is to investigate breaks in the rock for long lines where their parts are still buried, or to find a small piece showing on the surface that continues under the matrix.
Another in the field eroded piece. It appears to be a a disarticulated series of thoracic segments, but there is some work in the lab to determine if that is the case.
An isolated pygidial spine with the characteristic barbs. There could be more, but doubtful much more. Some time in the lab cleaning it up will say.
What looks like a pitiful, junky rock may actually be covering over a nice piece here. The more obvious component with the tubercles may point to this being a glabella.
More rocks that many people might not even bother noticing. But this is the trick with these rocks: anything that has a chance to be complete will be under a few thin (but tough) layers. Since the whole trilobite is covered in tubercles, any time I see a few tubercles isolated across the surface, that suggest the possibility that it could very well turn out to be impressive.
I suspect this is showing a glabella and a right cheek. With close inspection, one can make out that the tubercles appear at a few places on the surface, again suggesting a much more complete piece underneath the matrix.
These are not small trilobites, so the rocks one brings back will not be small. Be prepared to fill a bucket very fast. In this broken rock, at the top appears to be an outline. Ventral? Eroded?
Here is a lateral view of the break in the rock, the lower piece. Note the jagged line in the middle. That is the continuation of the trilobite. This will likely be a horribly difficult prep where at some point both halves will be glued together after I determine the orientation (ventral or dorsal). The obvious question might be, "why not trim a bit in the field and separate the overlying matrix from that line?" Absolutely not. The nature of this rock does not allow for that kind of easy separation; instead, going that route will just destroy the specimen.
The trick to finding good Terry specimens in this material is to look for traces on the surface and lines on the side, taking home the most promising pieces to be worked on in the lab with a scribe, abrasion, and eons of patience. Given the high percentage of hard chert, splitting these rocks is going to yield virtually nothing but disappointment or heartbreak. Anything good will shatter right through due to the chert that comes apart in jointed blocks and not clean bedding planes.
Do I have a nearly complete specimen in the last big rock? I won't know for a while. Unlike much easier formations and lithologies, one cannot just rely on clean splits or what is obvious. With this material, you have to take chances and bring what may be promising home for further work.