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Reference
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| Title: |
Report on Referred Fossils
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1966
(11/29)
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| Report by: |
Mackenzie Gordon
, Jr.
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| Referred by: |
Earl E. Brabb
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| | Age: | Carboniferous-Permian |
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| Comment: | This shell, although crushed so that its original shape can only be guessed at, preserves the sculpture and the early volutions sufficiently well to demonstrate its approximate position among the cephalopods. The narrow coiling of its early whorls shows that it is an ammonoid, rather than a nautiloid, despite the longitudinally elongate nodes along the umbilical shoulder that are reminiscent of certain nautiloides. It has fine transverse growth lirae encroaching upon the nodes, but lacks longitudinally directed lirea. The suture is not preserved.
The obivous noded ammonoid of this type that springs to mind is Gastrioceras and one might easily be satisfied to call it Gastrioceras? sp. and let it go at that. However, all of the Gastrioceras that we have in the USGS and USNM collections either have subcircular nodes, with wider interspaces, or diagonally elongate nodes.
The only ammonoid of which I am aware that develops longitudinally elongate nodes along the umbilical shoulder is a species of Glaphyrites (some call it Eoasianites) from the Lake Bridgeport Shale Member of the Graford Formation (Upper Pennsylvanian) in clay pits near Bridgeport, Texas. These nodes occur in specimens at diameters greater than 75 mm and the nodes are crude and not as well developed as in the Alsaskan form. In the Texas species the early whorls lack nodes and this, as far as can be determined, is true of the Alaskan specimen.
So, this is the dilemma I am in. Glaphyrites or Eoasianites is not supposed to possess nodes, but we know of one species that does and the crushed Alaskan specimen resembles it but certainly is not conspecific. In the absence of an Alaskan specimen that exhibits the suture pattern, one can only classify it as "gastrioceratid-like ammonoid indet." |
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