Protolenus sp. assemblage with Kingaspoides c.f. neglectus trilobites


An assemblage of trilobites on one plate featuring a new undescribed trilobite is now believed to be a Protolenus sp. after comparing it to what looks like a well preserved juvenile that appears strikingly similar to this larger trilobite.  At first I was not sure if this was real when I acquired the first specimen due to a lack of specimens on the market, and its odd preservation. 

Most Cambrian assemblages on the market are made up of a number of genuine Cambrian trilobites glued together onto one matrix.  Some of the trilobites on such assemblages have been heavily restored.  As long as the trilobites themselves are genuine and not heavily restored I don't see this as detrimental to studying them. 

What makes this assemblage unique is that the trilobites all seem to be natural to the plate and prepared and exposed exactly as they had died some 515 million years ago. The assemblage looks like it is from the Cephalopyge zone, Tissafinian stage judging by the smaller trilobites.  The location given is somewhat problematic as it is known more for Ordovician trilobites: Agdz, Draa Valley, Morocco.  From the Kingaspoides trilobites this plate is clearly in the same or near the same layer as the more well known trilobites such as the Acadoparadoxides briareus and the Hamatolenus vincenti. 

Notice above the "floating" trilobites that are prepped above the larger trilobite.  This shows it is a natural assemblage. The posterior portion of the thorax is slightly enrolled and the pygidium is not visible (overall 4" L 3.5" W). After having studied this trilobite once again from several angles I conclude that my earlier assessment may be in need of revision.  In my earlier study, I noticed that the unknown trilobite had characteristics that fit better with the sub-genus Protolenus (Hupeolenus) than with Hamatolenus (Myopsolenus).  The reasons are as follows: the glabella is tapered anteriorly and smaller in relation to the cranidium than most Hamatolenus; the extremely wide anterior border of the trilobite fits in with the main characteristic of the Hupeolenus sub-genus; finally, the long genal spine is a characteristic of the Hupeolenus. Hitherto, I did not have a working knowledge of this genus until I came across a specimen in my collection of unidentified trilobites.

However, I have serious doubts about the Hupeolenus diagnosis. The glabella is much more tapered on the Hupeolenus than in this specimen. The shape and furrows of the glabella match better with a Myopsolenus than with a Hupeolenus.  My Hupeolenus specimen lacks any eye details such as eye ridges or palpebral lobes so I can't compare with this specimen.  However, though it does not fit with the Hupeolenus diagnosis I have put the specimen back into the Protolenus genus, species unknown.  The main reason for this is that the genal spines are very different from the H. Myopsolenus type.

The palpebral lobes are short and do not reach the posterior furrow of the cranidium, and is better preserved on the left side. This maybe the eye lobe itself.  The glabella is similar to Collyrolenus staminops with parallel sides posteriorly with a tapered front anteriorly.  The pre-glabellar field (space in front of the glabella) which varies among the Protolenus and Hamatolenus genus, seems to be interrupted by the glabella or a portion of it. The whole of the cephalon has a very wide and concave anterior border, contrasting with the smaller trilobites except for one. 

The main point for diagnosing this as an Protolenus sp. (instead of an H.Myopsolenus) has to do with a smaller two inch example of the trilobite which I have gone into detail in an earlier page (Undescribed Protolenines).  This smaller trilobite is most likely a juvenile example of this larger trilobite.  This juvenile undescribed Protolenus has very long genal spines and a well formed anterior cephalic border.

 

In the above three smaller photos I show what looks to be a classic Kingaspoides c.f. neglectus (labeled 1), typically found in the Lower Middle Cambrian, Cephalopyge zone, Tissafinian stage.  The trilobite shows remarkable preservation especially on the cephalon.  Notice the furrow that separates the free cheek from the cranidium where the eye is located, clearly seen in the second photo.  The glabella is effaced but still visible (third photo) and the convexity of the front of the cranidium is clearly visible. The small spines on both sides of the free cheeks are well preserved.  Often the spines are not preserved.  The rest of the trilobite body (the thorax) is tightly connected to the cephalon.  There is a breakage on the thorax vertically but the shape and preservation is clearly seen in the first of the two photos above. The middle thoracic axis is wider than the right and left thorax. The pleural spines are also seen in the first photo.

The above trilobite is unusual in preparation as it sits on top of the genal spine. This shows the convexity of the cranidium typical of Kingaspoides c.f. neglectus very well, though missing the free cheeks and spines.

This trilobite is of an unknown genus, with a anterior border on the cephalon, a rectangular glabella more defined than on the Kingaspoides.  However, this preservation is not as good as the other examples above. The palpebral lobe is not preserved and there maybe restoration on one of the spines as they are of different length.  At first glance I thought it maybe an Ornamentaspis with a more defined glabellar area than the Kingaspoides, but the very wide and clear anterior border on the cephalon and the equally strong axial ring almost suggests a smaller juvenile of the larger trilobite, however, with no palpebral lobes showing and the shape of the glabella the identity of this trilobite is not clear. 

This trilobite though not as well preserved as the first one, shows the glabella of a Kingaspoides type very well.  The glabella is rectangular and the furrows are faint.  It is also unusual in that it floats above the Protolenus and is prepped in its natural position.  It shows partial enrollment characteristic of a defensive posture.

Kenjiro Hakomori 2015.6.22. (Revised 2020.5.23.)