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Separating Pliotoxaster Comanchei And Whitei


Solittletime

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Is the chief criterion for separating Pliotoxaster comanchei and Pliotoxaster whitei the locality in which they are found? I know that comanchei is reported from the Trinity, i.e., Glen Rose. However, has anyone find that species in the Fredericksburg, i.e., the Walnut, as well? Pliotoxaster whitei has been reported from the Fredericksburg, i.e., Walnut and Goodland, and also from the Washita, i.e., Duck Creek. The specimen from the Walnut is in the UT collection, PaleoCentral BEG21287, however, looks a little suspicious to me as the pore-pairs in the unpaired anterior ambulacrum don't look very inflected to me. The reason I am asking is I am having trouble finding a morphological feature that I can unequivocally distinguish comanchei from whitei. It appears that the periproct of comanchei is more visible in an aboral view and maybe the posterior paired ambulacra are somewhat shorter than in comanchei. Does anyone have a comment on that? The parafasciole also seems to be more conspicuous near the ambitus in whitei. Do you concur? Alternatively, do you have another morphological feature that you rely on?

Any help would be greatly appreciated.

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Is the chief criterion for separating Pliotoxaster comanchei and Pliotoxaster whitei the locality in which they are found? I know that comanchei is reported from the Trinity, i.e., Glen Rose. However, has anyone find that species in the Fredericksburg, i.e., the Walnut, as well? Pliotoxaster whitei has been reported from the Fredericksburg, i.e., Walnut and Goodland, and also from the Washita, i.e., Duck Creek. The specimen from the Walnut is in the UT collection, PaleoCentral BEG21287, however, looks a little suspicious to me as the pore-pairs in the unpaired anterior ambulacrum don't look very inflected to me. The reason I am asking is I am having trouble finding a morphological feature that I can unequivocally distinguish comanchei from whitei. It appears that the periproct of comanchei is more visible in an aboral view and maybe the posterior paired ambulacra are somewhat shorter than in comanchei. Does anyone have a comment on that? The parafasciole also seems to be more conspicuous near the ambitus in whitei. Do you concur? Alternatively, do you have another morphological feature that you rely on?

Any help would be greatly appreciated.

To your original question, I wouldn't think that any species determination in echinoids would or should be made based on locality. I don't have the specific references for each species, but I would start there to look for the characteristics defined to establish each as an individual species.

The human mind has the ability to believe anything is true.  -  JJ

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Actually, I do have the original references which really are not all that helpful. So, I am looking for any suggestions that anyone might have.

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  • 3 years later...

I have descriptions and pictures of both in my book - Fossil Echinoids of Texas.

 

Pliotoxaster comanchei   (Clark, 1915) - The photo is the Holotype.  The description is from the original Author.

The peristome is transversely ovate.

The posterolateral pair (ambulacra) being considerably shorter than the anterolateral pair. [the difference is less so than P. whitei].

 

Also, when viewed from above, the posterior end is broad compared to P. whitei.

 

 

 

Pliotoxaster whitei  (Clark 1893) - The description is from the original Author.

The peristome is transversely subpentagonal.

The anterolateral pair (ambulacra) are distinctly larger than the posterolaterals.  [the difference is more so than P. comanchei].

 

Also, when viewed from above, the posterior end is narrow compared to P. comanchei.

 

I hope that helps.

 

Bill

 

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According to the Echinoid Directory 09/2017 (By Kroh and Smith), Toxaster and Pliotoxaster are separate genus.

 

Pliotoxaster Fourtau, 1907

Petals straight.

Anterior and posterior petals of similar length.

Pore-pairs in ambulacrum III subpetaloid with elongate pores, but smaller than those in other ambulacra

and pore-pairs differentiated with interporal knob.

 

Toxaster Agassiz, 1840

Petals flexed.

Anterior petals generally much longer than posterior petals.

Pore-pairs in ambulacrum III laterally elongate and similar to those in the other ambulacra aborally.

 

Thanks, Bill

 

 

 

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