-- Morphologie / Morphology (
--- TOM for December (

Posted by goniagnostus on 01.12.2007 at19:34:

  TOM for December

This month's trilobite is a remarkably spiny one!
I invite you to view it at:
But here it is as a preview!

Enjoy, Sam [goniagnostus]

Posted by juniper on 01.12.2007 at22:04:

  RE: TOM for December

That looks like a textbook specimen...
The remains with shell preservation are easily detected, with fantastic colour and surface, including even some (parts) of the spectacular pleural spines.
Is the rest preserved as an impression?
Or has the circulating halo of spines been reconstructed, to render an idea of the complete shape of this beautiful trilobite?

Die Schalenerhaltung ist wirklich sehenswert. Sind die übrigen Partien als Steinkern erhalten?
Oder wurde der umlaufende Strahlenkranz form-ergänzt, damit man die vollständige Gestalt des Trilobiten nachvollziehen kann?

best regards

Posted by goniagnostus on 02.12.2007 at03:34:

  RE: TOM for December

Zacanthoides grabaui typically preserves largely as an internal mold, so this specimen, as you note, has a remarkably large amount of exoskeleton still present. The pleural spines are left as molds that show the extent of the original spines, and the negative piece matches it, so there is no reconstruction. Dave Comfort is an extremely talented and careful preparator, and he was so struck by the axial preservation (usually that part of the shell is lost entirely) that he was wondering if this was indeed Z. grabaui and not some related new species. However, other specimens of Z. grabaui, though not showing the spine, do show a depression in the posterior thorax and pygidium that is clearly an impression of the axial spine, so we are now quite confident in the identification. It is a remarkable piece!

Posted by Schachtratte on 02.12.2007 at08:21:


indeed. Nice bug

Posted by juniper on 02.12.2007 at18:27:

  RE: TOM for December

Thank you, Sam, for your comment.
It shows again, how important it is to examine the negative part of the fossil, and to keep it in the collection, too.
I guess, even for a very experienced preparator it is sometimes amazing, which kind of miracles may appear when splitting a stone...


Thank you for the translation "Steinkern" = internal mould :)
Yesterday I was unable to get that correct technical term...

Posted by Xiphogonium on 02.12.2007 at18:39:

  RE: TOM for December

Original von juniper
Thank you for the translation "Steinkern" = internal mould :)
Yesterday I was unable to get that correct technical term...

Indeed! :] "Unfortunately" the words mould and molt, which sound very similar and which are both being used frequently when referring to fossils, do seem to have a lot of fun in misleading and irritating non-native speakers of English! ;)

Posted by goniagnostus on 02.12.2007 at20:11:

  RE: TOM for December

I am continually impressed by the ability of posters here to communicate in English. You do not want to see me try to write something in german! ; )
And I have learned that steinkern = internal mold (to use the US spelling of mould).

Posted by Xiphogonium on 02.12.2007 at20:20:


Actually we don't have much choice! - Not only when it comes to fossil literature, etc. <g>

Posted by Andries on 02.12.2007 at22:58:


8o unbelieveable
I´m really impressed by this one.
You really have to be lucky, to split the stone leaving the axial spines.
I´m still amazed.

can you tell the size of this trilobite?

Posted by goniagnostus on 03.12.2007 at01:37:


I was told by Dave Comfort, who prepped the specimen, that it is 5 cm long, including the spines, which make up about the last 1 cm of length.

Forum Software: Burning Board 2.3.6, Developed by WoltLab GmbH