Trilobite Identification

[magicalmrmerlin]

Can anyone tell me which type of trilobite this is? I have no idea personally.

I know it came from Morocco. I got it from a UK dealer. Any other relevant information appreciated. Thanks for your help.

[kurdelmb]

It would appear to be some form of Greenops. Beyond that I have no exact information.

[piranha]

It is very similar to the asteropyginid Greenops, although this trilobite genus is: Hollardops. The common Devonian (Moroccan) species is Hollardops mesocristata, but the slender pygidial spines would suggest Hollardops burtandmimiae instead.

 

 

Morzadec, Pierre (2001)

Les Trilobites Asteropyginae du Dévonien de l'Anti-Atlas (Maroc).

Palaeontographica Abt.A, 262:53-85

 

 

 

[magicalmrmerlin]

Thank you very much for this helpful information. Do you guys know anything about how the eyes differ between trilobites - what should we be looking for generally? I chose this one because the eyes had some detail, it seemed nice for quite a cheap purchase.

[piranha]

On 8/11/2014 at 2:46 AM, magicalmrmerlin said:

...Do you guys know anything about how the eyes differ between trilobites - what should we be looking for generally?

 

 

Although it has been generally accepted since Jell 1975, that there are three types of eyes, more recently it has been suggested that there are only two types of eyes; holochroal and schizochroal. The abathochroal eye described only from eodiscid trilobites, is most likely a paedomorphic holochroal eye. 

 

text from:

 

Zhang, X-G., & Clarkson, E.N.K. (2012)
Phosphatized eodiscoid trilobites from the Cambrian of China.
Palaeontographica Abteilung A., 297(1-4):1-121   PDF LINK

 
The eyes of eodiscoids were described as abathochroal by JELL (1975b), who considered them to be distinct from holochroal eyes since the lenses were somewhat separated from one another, along with a summary that the eyes of eodiscoids resemble holochroal eyes in five respects, and there are eight differences from the schizochroal type. Of these, two key features for establishing these eyes as a separate type are the lenses not being in contact with any of the surrounding lenses, and each lens possessing its own corneal membrane. However, with more and more phospatized material being documented, and especially with the more fully detailed morphological examination of the visual surface of the eodiscid Pagetides, our new observations do not support the view that abathochroal eyes are distinct from the other two well-known types.
 
For instance, JELL (1975b) believed that each of the individual lenses carried its own corneal cap, but the fact that the outermost thin layer of the visual surface can flake off, taking with it many lenses together, rather than just a single one, casts doubt on this interpretation. Actually, the internal surfaces of some librigenae with the visual surface attached show that some of the fine lenses are polygonal in outline (Plate 16, Fig. 7), rather than circular as seen from the external surface. This is because these lenses remained in close contact as they grew towards a centre point of the visual system, and this has led to the deformation of the outline of lenses from circular to mostly hexagonal, as well as a few pentagonal and quadrilateral (also see ZHANG & CLARKSON 1990, pl. 2, figs 2-6). Moreover, it is now known that the juveniles of holochroal-eyed trilobites have separated lenses (CLARKSON & ZHANG 1991, CLARKSON & TAYLOR 1995), and that they are likewise separated in the paedomorphic Ctenopyge ceciliae (CLARKSON & AHLBERG 2002).
 
If eodiscoids are indeed paedomorphic derivatives of holochroal-eyed polymerid trilobites, is it not likely that they would have separated lenses too? It may be, therefore that the concept of abathochroal eyes as a separate eye type, though adopted earlier (CLARKSON 1997) is no longer sustainable, for the moment we leave the question open. In the descriptive part of the text, accordingly, we describe the eyes of eodiscids as abathochroal, because this term to date remains absolute as only known from eodiscoid trilobites.

 

[magicalmrmerlin]

I understand that it is quite hard to make a fake resin trilobite that has realistic detail on the eyes, like this one. That's the main reason I chose it. Mind you I don't know for sure. I was a bit concerned by the way it is set deep in the rock, in the thinnest part of the rock. My only worry was it could have been popped into some more solid rock for show, disguised by airbrush marks. My other one has little in the way of marks on the rick like this one.. This one also has a dab of glue on the bottom where the rock seems to have split in the process of preparation. So did some of the others in the tray with it. Is this a bad sign? I have two of these from the same dealer (as mentioned) - The other one is poorer quality and in a slightly browner rock. The rock colour is consistent on all sides in both cases. There is no glue at all on the second one. The second one is also less well prepared - there was a tiny bit of surface rock on the trilobite which I flicked off with a modelling knife. It revealed more trilobite underneath, which didn't crumble so I took that as a good sign. I can't see air bubbles in either.