Differents types of drotops armatus?

[LordWampa]

Hello I will tag you @piranha as I think you are the trilobite master. This is not a typical I have a fossil to ID post, is more why I see to different trilobites often tages as drotops armatus. What I am missing? Is there an explanation?

 

When I think of a drotops armatus, this is what I typically expect.

 

 

The main thing I see here is kind of long spikes and in the center section of the trilobite, the spikes are in pairs.

 

But then, you sometimes find this also labeled as Drotops armatus:

 

I did some research and seems to be 4 subspecies or forms?

D. armatus Struve, 1995

D. a. accurata Struve, 1995

D. a. perspinosa Struve, 1995

D. a. armata Struve, 1995

D. a. hoplites Struve, 1995

 

But I can't find more information. Is there some paper or place where this is described? I can't find the original paper

 

 

 

 

Edited January 2 by LordWampa

[piranha]

The subspecies concept applied to Drotops armatus has only appeared in one publication: Struve 1995.

 

Until additional research is published, the consensus continues to be one valid species: Drotops armatus.

 

 

"Neither specimen is assignable to 'forms' named by Struve (1995), because of uncertainty in size of sculpture elements and doubts as to whether all points where spines originate actually bore spines prior to preparation... ...More extensive and detailed work is necessary to give Drotops armatus a stable systematic position. Internal structure and many more specimens set in a detailed stratigraphic framework are needed to validate the multiple forms proposed by Struve."

 

Chatterton, B.D.E., McKellar, R.C. 2009
Early and Middle Devonian Phacopidae (Trilobita) of Southern Morocco.

Palaeontographica Canadiana, 28:1-110  PDF LINK

 

Struve, W. 1995
Beiträge zur Kenntnis der Phacopina (Trilobita). 18. Die Riesen-Phacopiden aus dem Maïder, SE-Marokkanische Pra-Sahara.
[Contributions to the Knowledge of Phacopina (Trilobita). 18. The Giant Phacopids from the Maïder, SE Moroccan Pre-Sahara.]
Senckenbergiana Lethaea, 75:77-129  PDF LINK

[LordWampa]

Thanks @piranha, so is there an explanation on the difference positions and number of spikes in some specimens? Or it could be considered similar to the case of deers having antlers of different forms in the same species (don't know if it's a stupid comparison)?

 

 

[piranha]

Struve concedes the same point from McKellar & Chatterton; many more specimens are required.

 

Spine distribution, frequency and length are the differences listed in the systematic descriptions.