Abgeschickt von Allart am 18 Maerz, 2004 um 12:32:06
Antwort auf: Re: Frage dazu: von Brigitte am 17 Maerz, 2004 um 23:00:50:
Hello Brigitte,
I think that some of these differences can be attributed to different kinds of preservation. Besides that, the reconstruction that is used by Senckenberg may be a bit misleading. How many examples are there of absolutely straight spines in arthropods except for median spines such as in Limulus (horse-shoe crab)? I think that the spines in the Senckenberg Radiaspis radiata drawing are a bit too straight. I have pygidia from the same locality as Ben's complete Radiaspis, all R. radiata, but all different. Some are long, thin and elegant, others are short, thick and robust. Such differences are not unusual in the Lichida order. Ceratarges armatus has the same differences. I have from one locality two pygidia and a nearly complete one, and they are all different in size, appearance, thickness of spines, etc.
There are studies concerning these matters, where for example different parts of the ocean cause different kinds of fossilisation. The concept that the best preservation exists only in anaerobic or dysaerobic conditions because there would be no microbal activity in those places has failed already. Indeed scavengers will not be present but there are anaerobic microbes that use other forms of oxigants to break down organic material. But besides this, the amount and composition of other raw materials that are available will influence the composition of the eventual fossil exoskeletons as well.
Best regards,
Allart
P.S. I have emailed you again today, yesterday's email seems not to have arrived
: Hey Allart,
: first thank you a lot for this nice octa picture. I didn´t know that species yet.
: What is irritating me is that the conspicious length and the fine structure of Ben´s first Radiaspis from Prüm and my, which originates nearly from the same region, differs, as I think, significantly from the others with more robust and stocky spines.
:
: :
: : Hello Brigitte,
: : Here is an example of a variant with different length of pygidial spines. It is Radiaspis octa, with 8 thoracic segments (in stead of 9) and 14 pygidial spines of which the median pair is fairly longer than the others.
: : Allart
: : http://members.lycos.nl/trilobite/time/octa.jpg
:
: :
: : : Hallo,
: : : ja, die Photos fehlen mir eben auch -
: : : wenn ich mir "unsere" aber so angucke, hätte ich Folgendes ganz gerne gewußt: gibt es eigentlich Radiaspisformen - Subspecies, was weiß ich - mit diesen ganz langen und andere mit kürzeren Pygidialstacheln?
: : : Wie ist das?
: :
: : :
: : : : mir fehlen die Photos von den rechtsrheinischen neufunden....
: : : : Der Meinung mit den 14 Stacheln am pygidium schließe ich mich in der weise an, dass ich Radiaspis sowohl mit 14 Stacheln aus dem Couvinien der Ardennen
: : : : http://www.magrean.de/triloweb/trilopics/collection/radiaspis_radiata_ardennen.jpg
: : : : als auch mit 16 Stacheln aus der Eifel habe...
: : : : http://www.magrean.de/triloweb/trilopics/collection/radiaspis_radiata1.jpg
: : : : So ganz klar ist das doch nicht...