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Missouri Trilobites


GerryK

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In addition to all of the excellent references suggested, this excerpt helps to detail the context of these features.

Phylogenetic instruction manuals are a good thing... I have a lot of reading and research on my plate emo73.gif:P

 

RE: Calymenid Trilobites from the Ordovician Rocks of Michigan

Journal of Paleontology, Vol. 32, No. 5 (Sep., 1958), pp. 943-960

Authors: Erwin C. Stumm and Erle G. Kauffman

 

Calymenidae Stumm.jpg

 

 

 

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  • 1 month later...

Trilobite Challenge:

This post is to test the TFF trilobite collectors knowledge of trilobite morphology. This trilobite looks like the usual Dalmanites. However, when prepping this Dalmanitid from Missouri, I noticed 2 features that are not typical of Dalmanites. Dalmanitids have produced many interesting morphological features but the ones on this trilobite are new to me. I sent this picture to 2 trilobite researchers and asked them if they have ever seen these features. They both said that they have never seen these on a Dalmanitid. So, the challenge to the TFF trilobite collectors is, can you identify the 2 unusual features on this Dalmanitid?

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The cheek lobes certainly look unusual. Still puzzling on the other features...

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The cheek lobes certainly look unusual. Still puzzling on the other features...

Why does it look unusual to you?

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... and the median glabellar notch?

Very good, this is an unusual feature but not one of the 2 I'm looking for.

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The inflation of the small lobes on the cheeks seems unusual to me. My other guess would be the associated ratios of length and width of the glabella, furrows and pits. If the answer is not that complicated than my focus would be the anterior margin. Looks like a transitional form in between a dalmanitid-odontochilid type. Looking forward to your follow-up on this intriguing trilobite.

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The inflation of the small lobes on the cheeks seems unusual to me. My other guess would be the associated ratios of length and width of the glabella, furrows and pits. If the answer is not that complicated than my focus would be the anterior margin. Looks like a transitional form in between a dalmanitid-odontochilid type. Looking forward to your follow-up on this intriguing trilobite.

You are correct. The swelling or small lobe on the free cheek in front of the eye is very unusual for a Dalmanitid. The other features are not that unusual. There is still one feature left.

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Eye size and position appears to be the next best guess. Looks more like an odontochilid in that regard.

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Eye size and position appears to be the next best guess. Looks more like an odontochilid in that regard.

Not unusual

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I think I finally solved it. The glabellar furrows are isolated and should be connected in Dalmanites. Attached are two figures that I assembled of a side by side comparison of morphological features in these trilobites. After spending a lot of time analyzing the orientation, position and ratios of the the furrows I kept missing the obvious element. The eye shape is more crescentic as well and that pushes me closer to Odontochile. According to the treatise the glabellar furrows are connected in some species of Odontochile as well. Where do you anticipate placing this trilobite?

 

Thanks for the great quiz :D

 

Dalmanites - Odontochile.jpg

 

RE: Exoskeletal architecture, hypostomal morphology and mode

of life of Silurian and Lower Devonian dalmanitid trilobites

Bulletin of Geosciences, 2008 - Volume 83(1). pp. 1-9

Petr Budil, Alan T. Thomas, František Hörbinger

 

 

 

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I think I finally solved it. The glabellar furrows are isolated and should be connected in Dalmanites. Attached are two figures that I assembled of a side by side comparison of morphological features in these trilobites. After spending a lot of time analyzing the orientation, position and ratios of the the furrows I kept missing the obvious element. The eye shape is more crescentic as well and that pushes me closer to Odontochile. According to the treatise the glabellar furrows are connected in some species of Odontochile as well. Where do you anticipate placing this trilobite?

Thanks for the great quiz :D

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RE: Exoskeletal architecture, hypostomal morphology and mode

of life of Silurian and Lower Devonian dalmanitid trilobites

Bulletin of Geosciences, 2008 - Volume 83(1). pp. 1-9

Petr Budil, Alan T. Thomas, František Hörbinger

Although your observations may be true, It's not an unusual feature. Interesting that your illustrations of the two Dalmanitids shows how different and unusual the Missouri Dalmanitid is.

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Famous last words :P :

On 6/16/2012 at 10:28 AM, piranha said:

I think I finally solved it.

 

 

Undeterred, I will offer another possible answer. The S3 lateral glabellar furrows appear to be quite indistinct in your specimen. Other than that I would fall back on the shape of the precranial process. Looking forward to your observations and how you decide to classify it.

 

Dalmanitid Glabellar Furrows.jpg

 

RE: Lower Devonian dalmanitid trilobites of the Prague Basin (Czech Republic)

Transactions of the Royal Society of Edinburgh, 99, 61–100, (2009)

Authors: Petr Budil, František Hörbinger and Robert Mencl

 

 

 

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Famous last words :P :

Undeterred, I will offer another possible answer. The S3 lateral glabellar furrows appear to be quite indistinct in your specimen. Other than that I would fall back on the shape of the precranial process. Looking forward to your observations and how you decide to classify it.

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RE: Lower Devonian dalmanitid trilobites of the Prague Basin (Czech Republic)

Transactions of the Royal Society of Edinburgh, 99, 61–100, (2009)

Authors: Petr Budil, František Hörbinger and Robert Mencl

The S3 furrow is not unusual for a Dalmanitid. Dalmanitids have many different types of precranial processes and this one is not unusual.

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Smiley_Sarcastic-WhiteFlag.gifwaving-white-flag.gifSmiley_Sarcastic-WhiteFlag.gif

Thanks for all your observations on this unusual Dalmanitid. There are 4 unusual features and you did identify one of the two I was looking for (the swelling on the free cheek) and one of the other 2 that are not as obvious (the anterior notch in the suture). I will post all 4 features once I photo two other cephalons to show the these features are consistent. Once I point out this feature, you'll all say "wow, that is different." Are there any other trilobite collects who want to try and identify the unusual feature before I post?

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squalicorax

Great Discussion. I tried to keep up but you lost me. All good. I still have a hard time telling Glyptambom and Dalmanites apart. Wicked Dalmanitid

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One more salvo on this bug? :o

The suture also appears to be unusual.

Instead of intersecting near the axial furrows it extends a considerable distance beyond the width of the occipital lobe.

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One more salvo on this bug? :o

The suture also appears to be unusual.

Instead of intersecting near the axial furrows it extends a considerable distance beyond the width of the occipital lobe.

:goodjob:
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This Missouri dalmanitid is an amazing trilobite. At first it looks like the usual Dalmanites. I have prepped many different species, seen many pictures and illustrations of dalmanitids and I have never seen anything like this trilobite. Dalmanitids have evolved many different types of morphological features and there are four features on this trilobite that are new to me. I've posted pictures of three cephala to show that these features are consistent and are numbered on one of the pictures.

The feature that is so unusual is the course of the facial suture. Typically, in a dalmanitid, the suture in front of the eye will generally follow the glabellar furrow and then the anterior part of the suture will follow the curvature of the glabella. See the line drawings posted above of the Dalmanites and Odontochile. This trilobite does not follow this pattern. Instead, the suture in front of the eye goes up onto the librigenal field (1). Then instead of following the shape of the glabella, the anterior suture is indented (2). This type of suture pattern I have never see in a Dalmanitid. Then on the librigenal field there is a large swelling (3) and then there is a smaller one posterior of the large one (4). Again, I've never seen swelling like these on a cephalon of a dalmanitid. I am suspicious that there is some connection between the deflection of the suture onto the librigenal field and the large swelling.

This trilobite is a new species of dalmanitid. If only the swellings are present, it would be another species of Dalmanites. However, the unique suture pattern is not typical of any dalmanited and I have no idea how this trilobite would be classified.

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Edited by GerryK
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This has been an amazing journey in to trilobiteology for a sub-novice like me, and it has been an eye-opener!

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The middle photo is the sharpest for illustrating all of the features. Especially the suture and smaller cheek lobe.

Any other bits and pieces or pygidia? That should be an interesting paper. Thanks for posting the new photos. :D

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Changing gears for a moment back to one of the previous Missouri trilobites you posted. While looking through the literature and trying to discover a similar dalmanitid I stumbled across a bizarre Australian phacopid with genal spines that reminded me of your undescribed Phacops cf. claviger. The phacopid from Australia is late Devonian and curiously has lost any trace of a vincular furrow. There are two species of Babinops differentiated by 61 eye lenses in B. minor and 81 for B. planiventer. The persistence of the genal spines into the holaspid stage for both species is confirmation of the spines as a generic character.

 

Babinops minor.jpg

 

RE: Patterns of extinction and recovery of phacopid trilobites during the Frasnian–Famennian

(Late Devonian) mass extinction event, Canning Basin, Western Australia

Geological Magazine - Cambridge University Press (2009), 146 : pp 12-33

Raimund Feist, Kenneth J. McNamara, Catherine Crônier and Rudy Lerosey-Aubril

 

 

 

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  • 2 weeks later...

This post will continue on more fascinating Dalmanitids of Missouri.

In Campbell's(1977) classic work on the trilobites of the Haragan Formation of Oklahoma, he introduce a new genus Huntonia (now Huntoniatonia). There is a discussion on the cephalic-pygidial contact on enrollment of Dalmanitids and illustrates an enrolled specimen of H. lingulifer and a line drawing reconstruction showing the relationship of the cephalon to pygidium during enrollment. Also introduced is Prosocephalus and there are illustrations of the enrollment pattern of Prosocephalus tridentifera and Prosocephalus palacea (see illustration below). He states (p. 76) "although no enrolled specimen has been found, it is clear from the matching of pygidia and cephalon that the tip of the anterior process of P. xylabion fits against the posterior extremity of the doublure, leaving two openings on each side."

Now for the first time articulated enrolled trilobites from Missouri are illustrated to confirm Campbell's enrollment reconstruction in Prosocephalus. Below, the enrolled specimens of Prosocephalus tridentifera (which is similar to Prosocephalus xylabion) and Prosocephalus palacea show Campbell's interpretation is correct.

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Truly spectacular discoveries... Thanks for posting these incredible trilobites. :fistbump:

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