Upper Santonian Guide Fossils

The fossils below were found in the Smoky Hill Member of the Blue Gate Shale (Mancos Group) in east central Utah. 

Desmoscaphites bassleri Reeside 1927, from the upper Upper Santonian.

Uintacrinus socialis Grinnel. 1876, from the middle Upper Santonian.

As reported in a poster by Bylund, Scheetz, and Kittrick, 2025

Scaphites leei Reeside, 1927, form I Cobban, 1969, also from the middle Upper Santonian,

Clioscaphites choteauensis Cobban, 1952, from the lower Upper Santonian.

Except for the crinoids they are all external molds of the shell.

Mancos Group Field Trip Guide

 

Revisiting the Cretaceous Mancos Group in Utah—problems, previous methods, and new perspectives on a world-class Cretaceous marine section.  James I. Kirkland, M. Ryan King, Kevin G. Bylund, 2025 

Clioscaphites from the Emery Sandstone

The Emery Sandstone

    The Emery Sandstone as exposed in western Emery County, Utah consists of 4 or 5 thin sandstone beds that thicken rapidly sub-surface to the west.  Cephalopods preserved in the formation, mostly as internal molds, include the Nautiloid Eutrephoceras sp., and the ammonites Placenticeras syrtale, Baculites codyensis, and Clioscaphites vermiformis in the lower beds and Desmoscaphites bassleri in the uppermost bed.  Desmoscaphites bassleri Reeside, 1927, is an Index Fossil for the Upper Santonian (Upper Cretaceous), Clioscaphites vermiformis (Meek & Hayden, 1862), for the Middle Santonian, and C. saxitonianus (Mclearn, 1929) for the Lower Santonian.

    The trouble with finding only a few fossils in a few beds is that intermediates always seem to creep into the section.  The main difference between C. vermiformis and the underlying C. saxitonianus is the strength of the sculpture, pointed tubercles in C. vermiformis, and insipient nodes in C. saxitonianus. The lobe of the suture is another difference, being trifid in C. vermiformis and mostly bifid in C. saxitonianus, but rarely preserved in Emery fossils because the phragmocones are usually crushed.

    Below are photos and 3D models of a couple of fossils from the lower Emery Sandstone (Garley Canyon Beds).  The upper photos show a typical C. vermiformis with its strong sculpture and pointed tubercles. The lower photos show a specimen from the lowest bed of the Emery, still with strong sculpture but without a pointed tubercle, more of a strong 90° rib.  The sculpture on the lower specimen is stronger than typical C. saxitonianus, even stronger than C. saxitonianus var. keytei Cobban, 1952 (which by itself could be a new species).  Not being one to split, it's probably best to leave it in C. vermiformis for now and just consider it an intermediate until more specimens or one showing the suture can be found.

Clioscaphites vermiformis.  Specimen, left, 3D Model, right.  From a sandstone bed in the middle of the Emery Sandstone.

Clioscaphites ?vermiformis, Specimen, left, 3D model, right.  From the lowest sandstone bed in the Emery Sandstone.

Ammonite Chamber Internal Mold

An internal mold of an ammonite chamber. Left, lateral view, right, apertural view

Two views of an internal mold of one of the chambers from the phragmocone of an ammonite (Prionocyclus macombi Meek 1876).  The chamber was hollow and probably filled with gas and a little liquid while the animal was alive, and was probably empty of any solids after it died.  How long it sat empty on the seafloor, and while it was being buried under sediment is unknown. Eventually, it was filled with what we have here, dark sparry calcite crystals. I imagine the crystals grew from the inner walls of the chamber towards the center until it was completely filled. You can see the siphuncle at the top of the chamber (the keel here is missing), and on the bottom, in the apertural view, you can see a notch where the keel of the preceding whorl would have fit.

Ammonites preserved in limestone or concretions are more often found this way because the surrounding shell was preserved uncrushed as the matrix around the shell hardened. Those found in sandstone or shale many times have the phragmocone and most of the chambers crushed unless the chambers were filled with sediment.

Sexual Dimorphism in Ammonites

Sexual dimorphism as represented by the ammonite Yezoites frontierense (Cobban 1952)

Macroconch (female) 38mm on the left, microconch (male) 18mm on the right

Previously referred to Scaphites frontierense, presumably, the female was much larger to carry eggs.  Many extant cephalopods (the Blanket Octopus for example) show the same relative (?) dimorphism with the males much smaller than the females.

Lower Ferron Sandstone and Juana Lopez Members of the Mancos Shale around the north side of the San Rafael Swell

In an attempt to show that the Juana Lopez Member of the Mancos Shale really does expose itself on the west side of the San Rafael Swell, I introduce some photos to help.

Lower Ferron east of Huntington (visible upper right).

Lower Ferron east of Huntington, these beds contain Prionocyclus hyatti near Mounds.  They also form a small cliff under the Ferron Sandstone south of here from Ferron south to Last Chance Creek.

Juana Lopez Member east of Huntington (visible upper left)  Prionocyclus macombi concretions in middle of cliff  (right) and P. wyomingensis concretions at top of cuesta across wash.

Juana Lopez Member east of Huntington.  The same thin platy siltstone beds that appear on the east side of the swell appear here with the same platy rubble littering the slopes.  The concretion beds are also the same.

Two beds of the Lower Ferron Sandstone with large round concretions just north of Mounds.  Lower bed contains the ammonite Prionocyclus hyatti along with many other mollusks.

Around the north side the Juana Lopez is still there above the Lower Ferron.

Juana Lopez Member just west of Cat Canyon where Highway 6 and 191 cut through the Farnham Dome just east of Wellington.  Prionocyclus wyomingensis beds at top of cuesta in middle distance (Light cliff), P. macombi concretions in middle of slope.  Farnham Unit of Lower Ferron Sandstone in foreground.  Some minor faults also in foreground, one duplicating the orange bed in center.

The same thin siltstone beds, the same platy rubble.

Lower Ferron Sandstone just below dark Juana Lopez Member, 1 mile southwest of Grassy Siding.  Coon Spring Sandstone Bed at base.  Brown concretion to left center is what's left of the P. hyatti beds at Mounds.

On the east side of the Swell, the beds above the Lower Ferron have been refered to the Juana Lopez.  The only real difference I can see is a couple (2) of thin (2cm max) calcarenite beds.  South and east of Green River the Juana Lopez has more and thicker calcarenite beds.

Juana Lopez Member just west of Grassy Siding, Mt. Elliot in right distance.  Prionocyclus macombi concretions form edge of middle cuesta, P. wyomingensis concretions form orange lip of upper cuesta.

 Here on the east side are the same thin bedded siltstone beds, the same platy rubble, and the same concretion beds with the same fossils.  The siltstone beds on the west side maybe get a bit thicker, up to 3 or 4 cm, even more reason not to refer them to the Blue Gate Shale.

References:

Dane, C. H., Cobban, W. A., and Kauffman, E. G., 1966, Stratigraphy and Regional Relationships of a Reference Section for the Juana Lopez Member, Mancos Shale, in the San Juan Basin, New Mexico, U.S.G.S. Bulletin 1224-H

Edwards, C., D. Hodgson, S. Flint, and J. Howell, 2005, Contrasting styles of shelf sediment transport and deposit in a ramp margin setting related to sea-level change and basin floor topography, Turonian (Cretaceous) Western Interior of central Utah, USA: Sedimentary Geology, v. 179

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

Adult size in Scaphites

Three adult specimens of Scaphites showing the size range.  The two on the left are probably progenetic dwarfs of contemporary full size species.  Pteroscaphites pisinnus (far left) from the Scaphites whifieldi Zone, undetermined example (center) from the Prionocyclus hyatti Zone, and Scaphites carlilensis (right) from the Prinocyclus macombi Zone.  Only adults grow a hook for a body chamber.  Sexual dimorphs have been reported for most Scaphites, with microconchs being about the same size as Macroconchs but a lot less inflated.  The genus Yezoites may show dimorphic size differences comparable to that shown above, but that is for another post.

Website back!

The website

www.ammonoid.com

Fossil Cephalopods in Utah

is back up and running

The Museum in Green River, Utah

 The Mancos Shale exhibit at the John Wesley Powell River History Museum in Green River Utah, is now open.  Along with a couple of dinosaurs and other murals, it is a very nice addition to the museum.  In the distance on the right you can see the ammonite I found and posted about back in this post, and after it was prepared in this post.

 

Here is a view of the specimen with the mural behind it.

  And the sign telling about the collection and preparation. 

And a few of the other ammonites I donated (the six on the left).  And more of the large mural behind it, unfortunately showing a wounded scaphite, or is that just the leftovers of a large marine reptile it just finished eating. ;)

Intraspecific variation in Forresteria

Forresteria alluaudi (Boule, Lemoine & Thevenin) 1907, from depressed, evolute, spinose to compressed, involute, almost smooth, a nice range of intraspecific variation. Is it any wonder why these, and some like these, were placed in 4 separate species in 3 separate subgenera (Reeside, 1932), Barroisiceras (Forresteria) forresteri, B. (F.) stantoni, B. (Alstadenites) sevierense, and B. (Harleites) castellense. Kennedy, Wright and Klinger (1983) put them all in synonymy with F. alluaudi.

Many ammonoids show intraspecific variation, including, for example, Placenticeras from the Cretaceous and, at least in my mind and experience, Anasibirites and Wasatchites from the Early Triassic. Found in the same bed or group of beds worldwide, to see one would tell you precisely what age the rock they were in is. Unlike the Triassic example, where there are differences in ornamentation and shape from one part of the world to another (maybe some kind of latitudinal or provincial thing), F. alluaudi is basically the same, that is different, wherever found.

Forresteria was named after the late Robert Forrester of Salt Lake City, Utah, who found the type material in southern Castle Valley, eastern Sevier County, Utah.

Scaphites hippocrepis and S. leei

Scaphites hippocrepis and S. leei, Early Campanian (Late Cretaceous) Scaphitids. A row of ventrolateral tubercles, an inner row of tubercles on the body chamber and a constricted collar at the aperture. Best seen on the micromorph of S. leei in #22 below, and on the macromorph in #27, are dorsal lappets.


Below is a drawing of the dimorphs of S. hippocrepis. The collar shows well but the dorsal lappet does not, at least not as well as on some of the other figures.

The lappets and their dorsal location on the aperture of the adult micromorph is the question at hand, just how much plasticity is there in the location of the lappets around the collar? Especially in their ancestors and descendants.

Figures from:

Cobban, W.A., 1969, The Late Cretaceous ammonites Scaphites leei Reeside and Scaphites hippocrepis (DeKay) in the western interior of the United States: U.S. Geological Survey Professional Paper 619, 29 p., 5 pls.

Juvenile heteromorph

Another small heteromorph from the Cretaceous Mancos Shale. This one has the body chamber preserved so it is freshly hatched or up to a few weeks old. 1mm diameter at widest point.

Calcite Heteromorph

A small portion of a heteromorph ammonoid, possibly Allocrioceras. This thing is only about 1.5mm long, photo taken through the eyepiece of my microscope. Dorsal side toward viewer, without impressed zone so it was completely evolute and probably open whorled, not enough preserved to tell if it was helical or not. From the Upper Cretaceous Mancos Shale, lower Upper Turonian Scaphites whitfieldi Zone.

Placenticeras syrtale

Placenticeras syrtale prepared and ready for display

It may end up in the John Wesley Powell River History Museum in Green River, Utah

Uintacrinus and Desmoscaphites bassleri

Uintacrinus from the Mancos Shale

a small fragment of Desmoscaphites bassleri

These fossils were found by Rod Scheetz (BYU Museum of Paleontology) in the Mancos Shale southeast of Green River. The small fragment he found closely matchs the one I found (see Aug. 12, 2009 post). I am now quite sure they are D. bassleri, and the small Scaphites is S. leei, from the Latest Santonian. D. bassleri has been found in the Upper Emery Sandstone northwest of Price and Northwest of Green River, so the Lower Emery Sandstone or it's equivalents are probably not present south and east of Green River as the fossils I found were in the lowest concretions above the Scaphites depressus (Latest Coniacian) beds.

REF:
Landman N. H. and Cobban W. A., 2007, Redescription of the Late Cretaceous (late Santonian) ammonite Desmoscaphites bassleri Reeside, 1927, from the Western Interior of North America. University of Wyoming, Rocky Mountain Geology, v.42, no.2, p.67-94

vermiformis? Beds

a small Scaphites from low in the ?Lower Emery SS beds of the Mancos Shale east of Green River.

Body chamber from Clioscaphites ?vermiformis. These seem to have a lot more ribs than typical C. vermiformis.

Scaphitoid

Scaphitoid Cephalopod, Yezoites, possibly a new species.

A canyon cut through the Ferron Sandstone

Mancos Shale

More from 3-21-09 Field Trip

Alex, in the center,
watching as I uncovered the big one.
He likes ammonites as much as I do.

this is the sign Alex had pinned to his pack. A future Paleontologist for sure?

Looking for Prionocyclus at Stop 2

Looking for Scaphites at Stop 1

3-21-09 Field Trip

Jim Kirkland, State Paleontologist, holding the large Placenticeras syrtale

Folks admiring another large ammonite

Wraping up some of the peices of the big one

Like a Rainbow

Shes like a rainbow
Coming, colors in the air
Oh, everywhere
She comes in colors