Abgeschickt von Allart am 07 Maerz, 2004 um 13:37:03
Antwort auf: Unterschied Geesops - Reedops von Volker am 07 Maerz, 2004 um 13:31:18:
Hallo Volker,
There has been a crash in the older forum here, where a discussion took place about Phacops latifrons and Vireux-Molhain. There are two Phacopinae in Vireux which are Geesops sparsinodosus gallicus and Pedinopariops richterianus. I've posted a summary of the old discussion below.
Good luck!
Best regards,
Allart
Phacops latifrons is a name that is used in literature frequently, however mostly wrongfully. It appears in old works by famous Ardennes scientists such as Mailleux, and the popularity of this name has grown throughout the years to a point where it is used for many of its relatives even today. It is clear that a hiatus occurs in the knowledge of a great deal of people including scientists, about Phacops latifrons and relative species: all the Belgian (Ardennes) and French (Vireux Molhain, N.France) specimens of Phacops latifrons that I have seen turned out to be something else. The chase was on for the true geographic and stratigraphic appearance and characteristics of Phacops latifrons.
1. The reason for the discussion was that I could not believe something that the chairman of a Belgian paleontology club told me about statements made by Kowalski in 1989. If that what he told me was correct, then it is "impossible that Phacops latifrons is found in the Belgian Ardennes or the famous finding-place near Vireux-Molhain" and "all trilobites from either areas determined Phacops latifrons are in fact Pedinopariops richterianus".
Also, I provided photographs of several cephala collected in the Upper Eifelian and Lower Givetian (the gUpper Givetianh in the original message was a type error) of the Ardennes that I thought could be Phacops latifrons based on the amount of lenses in their eyes.
http://members.lycos.nl/trilobite/trilotarium/pages.html
2. Andreas knew the contents of the Kowalski article and he was able to inform us that according to Kowalski (1989) the appearance of Phacops latifrons is restricted to the German Junkerberg Schichten. Andreas told us that he has got a P. latifrons from the Ahrdorf Schichten (Gees) which is already in contradiction with Kowalskifs statement. Also, Andreas wrote that the possible P. latifrons cephala that I had found in the Eifelian and Givetian of the Ardennes were not members of the genus Phacops but rather of Nyterops. The Givetian cephala could not be P. latifrons at all because that species does not appear beyond the Eifelian boundary.
3. Andreas made clear one of the main differences between Phacops and its former subgenera. Genuine Phacops do not have a small rim strip bordering the cephalon which could be seen in the Ardennes cephala discussed, and the fact that their lenses vary from 4 to 5 per dorsoventral file contradicted P. latifrons as well. P. latifrons should have 3 to max. 4 lenses per dorsoventral file and the appearance of a sort like amount of lenses that exceeds the limit of 4 lenses per dorsoventral file combined with the shape of the glabellar sculptures that can be seen in the discussed Ardennes cephala strongly suggest that this is the genus Nyterops.
The difference in borders of the cephala of Phacops and relative genera can be observed in the following two cephala that Andreas made available:
Geesops schlotheimi (with an evident small rim around the cephalon):
http://www.trilotarium.de/forum_images/Phacops/Phacops_latifrons/Phacops%20latifrons%20vom%201.2.2004%20SIMG1400.jpg
Phacops imitator (close relative to P. latifrons; with no small rim):
http://www.trilotarium.de/forum_images/Phacops/Phacops_latifrons/Phacops%20latifrons%20vom%201.2.2004%20SIMG1118.jpg
4. Ben informed us that the age of the famous finding-site gMur des douaniersh near Vireux-Molhain is a subject of discussion itself and that its age lies around the Emsian-Eifelian boundary. In a conversation with Jacques Godefroid -a brachiopod expert from the Belgian Royal Institute for Natural Sciences- that I recently had, it turned out that they did not know the exact division either. Phacops latifrons is an Upper Eifelian species and the fact that the Upper Eifelian does not appear in Vireux, makes it extremely incredible that Phacops latifrons would appear there. In the Ardennes however, Upper Eifelian outcrops do appear and so the possibility that Phacops latifrons is found there cannot be denied, certainly not when considering the common origin of the rocks in both the Ardennes and Eifel. Ben provided the following link to a photograph of a Phacops latifrons that he had found in the Ardennes:
http://www.magrean.de/triloweb/trilopics/phacops_n_sp_50_50_ard005.jpg
5. Returning to Vireux-Molhain, the rocks in that region appear to range from Lower Emsian (where Homalonotids appear) to Lower Eifelian but Walter wrote that in the famous finding-site two relatives of Phacops latifrons appear according to Struve (1982). Lenscodes of both subspecies are given (VR or dorsoventral files / OC or max. lenses per file).:
Pedinopariops richterianus ssp. (18/7-8)
Geesops sparsinodosus gallicus, (18/5)