Straparollus (Euomphalus) Gastropods from the Permian Fort Apache Limestone East of Payson

Updated  10/16/17

 This is the only planispiral gastropod to be had in any quantity in the Fort Apache Limestone. The size range of specimens is huge, ranging from pinhead size microscopic juveniles up to six inch monsters found impressed in the limestones. And to add as a bonus - two species are found here in this formation. Straparollus gastropods are unusual in that they have a nearly square cross section of their tubes, and are quite flat on the sides as well. While most Straparollus are rimmed with a linear continuous rib on the outer coils, Straparollus Kaibabensis is nearly unique in that it has nodes or tubercles along its coils instead. This makes it appear at first glance to be a nautiloid, however without any septa or the pear shape opening cephalopods have, they are simply huge gastropods. Winters found both types as well in his GSA Memoir 89 from outcrops all on the Fort Apache Indian reservation.

Our finds include many silicified specimens, most partials, and several limestone impressions as molds. Also, they can be very small indeed, the smallest members are best seen in the microscope at 30x magnification. This contrasts with the monstrous specimen we found back in 2006 that was over six inches in diameter!

Straparollus (Euomphalus) Kaibabensis - Quick Cam shots

 The outer 2 or 3 whorls is where the nodes develop in mature specimens. This partial outer arc shows them very well. The entire outside rim of the shell is wider as a result of these ornaments.

 Strongly low angle top lit, this shows the nodes well. Same specimen.

 Dorsal view of the same conch, which you can see the swelling of the width for every node present. This also gives it a very nautiloid like appearance.

 Inside view shows the double wall that is characteristic of Straparollus. This is another feature that differentiates it from nautiloids in the field.

 On this one the outer whorls still easily shows the nodes in this low light shot. This specimen was left attached to the limestone on the lower right as to give it a handle to more easily position the specimen.

 Top view of same specimen, showing nodal swellings.

 Inside view - No septa to be found here! The wall thickness is amazing.

 Other side view same specimen.


Straparollus (Euomphalus) Kaibabensis - Digicam Shot

 This big fella was found back in 2006 on an expedition with some museum members on an exploratory hike. I hauled this one back in my back pack over 2 miles to the truck. Its preservation is poor, but you can easily see the nodes. A modeling clay cast was made of this one to show it as a positive cast below.

 Modeling clay cast of above to show positive relief. The nodes are easy to see and the curvature of the conch is evident. This took 4.5 pounds in clay to do...

 Another limestone impression of a smaller specimen. We practiced our clay molding on this one to test the technique. Talcum powder was used as a mold release, since the clay was white anyway. Worked really well!


Straparollus (Euomphalus) sp. - Microscope shots

 Juveniles all together at 7x. The one at the lower left shows the protoconch, and others already shows the linear ribbing of Straparollus sp. Note also in the juveniles, sometimes the coils don't touch. This is a defining character of Straparollus.

 A gorgeous miniature Straparollus! You can see the coils have gaps between them here as well. The ridges and nodes have not developed yet.

 This juvenile is starting to show the beginnings of the linear ribbing. It will grow very fast.

 This one was just nice to show the inner coils and protoconch well, and a section of the outer whorls forming the square profile with linear ribbing. It is still to early to tell if it will have nodes.

 A beautiful specimen already showing its linear ribbing. Its pretty big at this point, about 1 cm in size. Notice how the rib fades in height as it nears the center.

 Some non ornamented outer whorls of a regular Straparollus sp.


Straparollus (Euomphalus) sp. - Quick Cam Shots

 While a bit distorted from compression of overlying sediments, this complete specimen shows the linear ridges well and detail all the way into the protoconch. I left it in the limestone along with some beautiful cone shaped gastropods for a composite view of the sea bottom. It almost looks as if its sitting in the bottom muds.

 Closer view of above specimen. It would probably have fallen apart if I had continued to acid etch the limestone, so I stopped.

 Growth lines in one of the middle whorls, as an internal cast.

 The double shell structure of Straparollus is well seen here in this end on view which is the above specimen. This would have been to strengthen the huge conch as is grew to larger sizes.

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