Turonian (Late Cretaceous) Ammonites

Turonian age rocks are the most widespread cephalopod bearing rocks in Utah. The Tropic Shale in the south, the Frontier Formation in the north and northeast, and the Tununk , Ferron Sandstone , and Juana Lopez Members of the Mancos Shale in eastcentral Utah. These rocks were deposited in the Sevier Foreland Basin .

Ammonite Biozone

Prionocyclus quadratus
Scaphites corvensis

Prionocyclus novimexicanus Scaphites nigricollensis


Scaphites whitfieldi

Prionocyclus wyomingensis
Scaphites ferronensis


Scaphites warreni

Prionocyclus macombi

Prionocyclus hyatti
Scaphites carlilensis

Prionocyclus percarinatus

Collignoniceras woolgari Collignoniceras woolgari regulare


Collignoniceras woolgari woolgari

References: Cobban, W. A., 1951, Scaphitoid Cephalopods of the Colorado Group, U.S.G.S. Professional Paper 239; Cobban, W. A., 1976, Ammonite Record from the Mancos Shale of the Castle Valley-Price-Woodside Area, East-Central Utah, B.Y.U. Geology Studies Vol.22, Pt.3; Molenaar, C. M., and Wilson, B. W., 1990, The Frontier Formation and Associated Rocks of Northeastern Utah and Northwestern Colorado, U.S.G.S. Bulletin 1787-M; Molenaar, C. M., and Cobban, W. A., 1991, Middle Cretaceous Stratigraphy on the South and East Sides of the Uinta Basin, Northeastern Utah and Northwestern Colorado, U.S.G.S. Bulletin 1787-P;  Kennedy, W. J., Cobban, W. A., and  Landman, N. H.,  2001, A Revision of the Turonian Members of the Ammonite Subfamily Collignoniceratidae from the United States Western Interior and Gulf Coast, American Museum of Natural History Bulletin 267.

See rocks of the Ferron Sandstone or the Juana Lopez member

representative Turonian Ammonites below

Top from Left: Placenticeras pseudoplacenta Hyatt 1903, Prionocyclus hyatti Stanton 1893 gracile form,
Scaphites ferronensis Cobban 1951, Pteroscaphites sp. (regular and enlarged) found with S. ferronensis
Bottom from Left: Coilopoceras inflatum Cobban and Hook 1980, Prionocyclus hyatti robust form,
Prionocyclus macombi Meek 1876, and Prionocyclus wyomingensis Meek 1876, the large one is 75mm dia.

Coilopoceras inflatum Cobban and Hook 1980
this specimen is 100mm dia., a compressed dimorph,
found with Prionocyclus macombi in the middle of the Juana Lopez Member of the Mancos Shale

Juana Lopez Ammonites

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