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Reference
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| Title: |
Report on Referred Fossils
,
1969
(10/23)
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The following report is based upon two collections of ammonoids just brought to me by J.T. Dutro for examination. The only recognizable forms are lirate gastrioceratids, which in the United States are generally lumped together und a single genus, Pseudogastrioceras. In Russia the same shells are referred to four genera: Pseudogastrioceras, Uraloceras, Altudoceras, and in part Paragastrioceras. All of these are Permian. As the Alaskan shells probably belong to a new species, additional material from this locality would be highly desirable. |
| Report by: |
Mackenzie Gordon
, Jr.
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| Referred by: |
Donald H. Richter
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| | Age: | Permian |
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| Comment: | Two species of Pseudogastrioceras are recognized in these collections. One has nodes on the umbilical shoulder and rather strong longitudial lirae. The other is without nodes and has finer lirae. It resembles Uraloceras involutum from the lower Artinskian beds of Russia, but is slightly more evolute. It also resmebles P. fortieri Harker from the Assistance Formation in the Grinnell Peninsula, Arctic Archipelago, but is narrower and more evolute. These Alaskan forms have more lirae and are more evolute than species from West Texas. They resemble some of the larger specimens from our collections from the Meade Peak Member of the Phosphoria Formation, which have not as yet been identified within the immature examples upon which the published names are based. Similar forms occur in the Artinskian and Svalbardian stages in the U.S.S.R. and in arctic regions, also in rocks principally of Leonard age in the U.S. Based on similarity of shape and sculpture, an Artinskian age would seem most likely for the Alaskan specimens, but this may be more apparent than real when one considers the absence of typical marine sediments in the middle and upper parts of the Permian of the U.S.S.R. which overbalances the scale in favor of an early early age. Actually, because the genus Pseudogastrioceras ranges through Permian, the only positive statement possible is that these fossils are Permian in age. Because in this phylogenetic group the umbilicus tends to become smaller with time, a very late Permian age is unlikely. |
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