Permian Scaphopods from the Fort Apache Limestone

[Arizona Chris]

HI all,

 

Our latest finds from the acid fines from our new site on the Mogollon Rim - Scaphopods (Tusk Shells) from the Permian Fort Apache Limestone East of Payson.

 

A minor but very important faunal element in the upper early Permian Fort Apache Limestone are Scaphopods - Or more commonly known today as "Tusk Shells". These mollusks were conical tubes - some linearly ribbed some smooth, with both ends open for water current movement. Fortunately for us, In 1963 White, in his monumental GSA Memoir 89 had found the smooth scaphopods, and identified them as Plagioglypta. We also found a smaller number of ribbed scaphopods which were a different genus. The most complete scaphopod material never had transverse ribs, even in their juvenile sections.

 

About Preservation

A wide range of sizes of scaphopods were found, ranging from millimeter sized diameters to nearly a centimeter. The larger conchs were usually flattened and many cracked under the pressure of the overlying sediments. About half of them were still filled with terriginous material after dissolution in acid, and only the short sections were free of internal sediment. Most were seen to have a curved profile, especially the juveniles.

 

Smooth exterior (Plagioglypta canna)

 Four sections of Plagioglypta, with varying degrees of flattening. (7x) A complete specimen would have been up to 80mm long.

 

Although poorly preserved in white silica, this pair of nearly complete tiny scaphopods shows the curving nature very well.

 

Three more with varying amounts of curvature.

 

One of the largest flattened specimens.

 

Section of a large scaphopod.

 

End on view showing wall thickness. The top is cracked inward from the overlying sediment pressure.

 

Dentalium sp.

 

Linearly ribbed exterior (Dentalium sp.)

 

The ornamented exterior of this genus is stunning under the side lighting!

 

Worn piece with the larger part at bottom having its ribs worn smooth by wave action.

 

Close up of linear ribbing.

 

Thanks for looking!  

 

[ynot]

Thanks for showing these.