from the Mancos Shale in East-Central Utah
Shown from youngest
(on top) to oldest
all about natural size
Prionocyclus wyomingensis Meek 1876
Prionocyclus novimexicanus (Marcou) 1858
Gracile form of P. wyomingensis
on left was
found associated with Scaphites cf. S. whitfieldi
Clawson. The ammonite on the right is the robust form of P.
found with S. whitfieldi
high in the Juana
Lopez Member S.E. of Green River. P. wyomingensis
double row of ventro-lateral nodes while P. novimexicanus
single row, with a groove on each side of the keel.
See parts of a crushed P. novimexicanus?
Ammonites from the P. novamexicanus Biozone
Gracile form on left, robust form on right, both associated with Scaphites
cf. S. ferronensis
. These ammonites can be found all along
the outcrop of the Juana Lopez Member from east of Ferron, around the
north end of the San Rafael Swell, to the Colorado border.
See a large adult P. wyomingensis
Ammonites from the P. wyomingensis Biozone
Gracile form on left, robust form on right. From the Juana Lopez
Member S.E. of Green River. P. macombi has a single row of
ventro-lateral clavi and low flattened ribs.
See a large adult P. macombi here
Ammonites from the P. macombi Biozone
Gracile form on left, robust form on right. Found in the lower
Ferron Sandstone Member near Mounds. P. hyatti has a much wider
umbilicus than the other prionocyclids.
Ammonites from the P. hyatti Biozone