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 

Early Dienerian Ammonoids

Gyronites rigidus (Diener) 1897

 EARLY DIENERIAN AMMONOIDS AND NAUTILOIDS AND A NEW LATE GRIESBACHIAN AMMONOID SITE FROM THE DINWOODY FORMATION (THAYNES GROUP) AT CRITTENDEN SPRINGS, ELKO COUNTY, NEVADA James F Jenks, Takumi Maekawa, Yasunari Shigeta, David Ware, Arnaud Brayard, Kevin G Bylund, Daniel A Stephen, Noreen Kittrick, 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.

Devonian Orthocones

Devonian Actinoceratids in the Fitchville Formation on Wanlass Hill.  Found by David Johnson earlier this year and reported to me :)  I went out with him and a few other students to check them out earlier this year.

 

Also, some nice coral (Syringopora)

 

Early Triassic Stomatopod

Smith CPA, Aubier P, Charbonnier S, Laville T, Olivier N, Escarguel G, Jenks JF, Bylund KG, Fara E, Brayard A., 2023, Closing a major gap in mantis shrimp evolution - first fossils of Stomatopoda from the Triassic, Bulletin of Geosciences, volume 98, issue 1; pages: 95 - 110 

 Abstract:

Mantis shrimps (Stomatopoda) are marine benthic predators well known for their raptorial claws that have, through time, evolved into unique structures with exceptional stunning, piercing or even dismembering functions. Known since the Carboniferous, Stomatopoda fossils have started providing insights into the rise of these predators, however, major gaps in the fossil record remain. In particular, neither Permian, nor Triassic specimens have ever been uncovered. Such a long hiatus strongly hinders our understanding of their evolutionary history, especially regarding the transition between Palaeozoic and Mesozoic forms. We here report two mantis shrimp specimens from the Early Triassic Paris Biota of Idaho, USA, formally described as Triassosculda ahyongi gen. et sp. nov., partially closing an over 100 myr gap in the fossil record. Despite being incomplete, these specimens present distinct and well-preserved diagnostic characters on the posterior trunk and the tail fan. The telson shows a triangular shape closely resembling that of Palaeozoic mantis shrimps. The broadness of both the pleon and anterior rim of the telson, however, differs from that of most Palaeozoic forms, which have an overall narrow telson, and is more similar to that of modern representatives of Stomatopoda. Additionally, the uropodal exopods of Triassosculda ahyongi gen. et sp. nov. presents a considerable number of movable spines that are common among Jurassic and more recent taxa, but that have never been reported among Palaeozoic Stomatopoda. These features further support and above all, allow temporal refinement of previously suggested evolutionary scenarios. In the latter, and as for other major clades of crustaceans, Stomatopoda are assumed to have evolved from a shrimp-like morphology with a narrow triangular telson to a more lobster-like one with a broad and rather square-shaped telson. Triassosculda ahyongi gen. et sp. nov. indicates this transition was underway by the Early Triassic.

More Taxonomy

A new paper just out trying to update the nomenclature and authorship of ammonoids:

The higher taxonomic nomenclature of Devonian to Cretaceous ammonoids and Jurassic to Cretaceous ammonites including their authorship and publication

Hoffmann, René; Howarth, Michael K.; Fuchs, Dirk; Klug, Christian; Korn, Dieter

It may be the latest but it won't be the last.  I'm sure that just like those back in the fifties they're getting close to something natural. This should last 70 years just like the old scheme, with plenty of differing options in the interim.  

Paris Biota Decapods

The Paris Biota decapod (Arthropoda) fauna and the diversity of Triassic decapods

Abstract
We describe here the early Spathian (Early Triassic) Paris Biota decapod fauna from the western USA basin. This fauna contains two taxa of Aegeridae (Dendobranchiata), namely Anisaeger longirostrus n. sp. and Aeger sp. that are the oldest known representatives of their family, thus extending its temporal range by 5 Myr back into the Early Triassic. This fauna also includes two representatives of Glypheida (Pleocyemata) with Litogaster turnbullensis and Pemphix krumenackeri n. sp., confirming for the former and extending for the latter the temporal ranges of their respective superfamilies back to the Early Triassic. Overall, the Paris Biota decapods are some of the oldest known representatives of Decapoda, filling in an important gap in the evolutionary history of this group, especially during the Triassic that marks the early diversification of this clade. Additionally, we compile and provide overviews for all known Triassic decapods, which leads to the revision of four species of Middle and Late Triassic Aegeridae, and to a revised family assignment of a Middle Triassic Glypheida. Based on this refined dataset, we also investigate decapod diversity throughout the Triassic. We show that the apparent increase in decapod taxonomic richness is probably driven by the heterogeneity of the fossil record and/or sampling effort, and that the decapod alpha diversity is actually relatively high as soon as the Early Triassic and remains rather stable throughout the Triassic.

Cephalopod Phylogenetics

The more things are found to be the same the more they are found to be different. It may never end

Pohle et al. BMC Biology (2022) 20:88 https://doi.org/10.1186/s12915-022-01284-5

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.

The Canadian System (Period) as proposed by Flower (1957)

Because the Cephalopods were so different, Rousseau H. Flower wrote proposing the Canadian System with four divisions of unspecified rank (Flower 1957 p. 17).  Quoting from Flower:

"Faunally, the Canadian is relatively isolated from the Ordovician above and is characterized by stocks of its own. In the cephalopods..., the Canadian-Ordovician boundary involves changes never lower than of generic rank, and generally of the rank of families and orders."

Someone looking at only, or mostly Cephalopod fossils could see the column this way. The four divisions are areas where Flower collected cephalopods. The Cassinian from the Ft. Cassin area in Vermont, the Jeffersonian from the Adirondacks in NY, the Demingian from the Florida Mts. in New Mexico, and the Gasconadian from the Ozark Mt. area of Missouri. I don't think his later collections in Utah and Nevada changed anything.  His boundary is just above Zone K, which is basically the Hesperonomiella minor bed (e.g. Li and Droser 1999) or the base of the Whiterockian Stage of the Ordovician.

Chart modified from Flower 1964 (p. 23, fig. 3) Ross-Hintze Zones on the right.

These days, the Canadian System of Flower (later referred to as the Canadian Series) has been replaced with the Ibexian Series (Ross et al., 1997) and the Lower Ordovician Series of the ICS.

References:

Flower, R.H., 1957, Studies of the Actinoceratida, Memoir 2, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.

Flower, R.H., 1964, The Nautiloid Order Ellesmeroceratida (Cephalopoda), Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.

Li, X., and Droser, M.L., 1999, Lower and Middle Ordovician Shell Beds from the Basin and Range Province of the Western United States (California, Nevada, and Utah) PALAIOS, V. 14.

Ross, R.J., Jr, Hintze, L.F., Ethington, R.L., Miller, J.F., Taylor, M.E. & Repetski, J.E., 1997, The Ibexian, lowermost series in the North American Ordovician. United States Geological Survey Professional Paper, 1579-A.

Wiping the smile off the face of the horizontal Nautiloid

The cover of New Mexico Bureau of Mines & Mineral Resources Memoir 32 (1977), and the description from inside the front cover (below) (both used with permission from the New Mexico Bureau of Geology and Mineral Resources).  Showing the contented and smiling face of an orthoconic cephalopod with cameral (or siphonal) deposits counterweighting the gas-filled phragmocone letting it float horizontally and getting its face "out of the mud".  The non-counterweighted forms with disgusted frowns floating vertically (or about to).  I've had a smile on my face ever since first seeing this paper over 30 years ago just thinking of how happy the nautiloids on the cover were. 

All that changed the other day when I got a copy of Peterman & Ritterbush 2021 Vertical escape tactics and movement potential of orthoconic cephalopods PeerJ 9:e11797. Which lead to: Peterman, D.J., Barton, C.C., and Yacobucci, M.M., 2019 The hydrostatics of Paleozoic ectocochleate cephalopods (Nautiloidea and Endoceratoidea) with implications for modes of life and early colonization of the pelagic zone Palaeontologia Electronica Article number: 22.2.24

Needless to say, I now have to re-arrange the thoughts of horizontal nautiloids having smiles and put the smile on the vertical nautiloid.

This might be just as hard as giving up the Geosynclinal Theory I was taught back in 1972.

:)

More exceptional fossil assemblages

 Adding to localities where fossils like those in the Paris Biota are found.

Smith, C.P.A., Laville, T., Fara, E., Escarguel, G., Olivier, N., Vennin, E., Goudemand, N., Bylund, K.G., Jenks, J.F., Stephen, D.A., Hautmann, M., Charbonnier, S., Krumenacker, L.J., & Brayard, A., 2021, Exceptional fossil assemblages confirm the existence of complex Early Triassic ecosystems during the early Spathian. Scientific Reports 11, 19657 (2021). https://doi.org/10.1038/s41598-021-99056-8

Abstract

The mass extinction characterizing the Permian/Triassic boundary (PTB; ~ 252 Ma) corresponds to a major faunal shift between the Palaeozoic and the Modern evolutionary fauna. The temporal, spatial, environmental, and ecological dynamics of the associated biotic recovery remain highly debated, partly due to the scarce, or poorly-known, Early Triassic fossil record. Recently, an exceptionally complex ecosystem dated from immediately after the Smithian/Spathian boundary (~ 3 myr after the PTB) was reported: the Paris Biota (Idaho, USA). However, the spatiotemporal representativeness of this unique assemblage remained questionable as it was hitherto only reported from a single site. Here we describe three new exceptionally diverse assemblages of the same age as the Paris Biota, and a fourth younger one. They are located in Idaho and Nevada, and are taxonomic subsets of the Paris Biota. We show that the latter covered a region-wide area and persisted at least partially throughout the Spathian. The presence of a well-established marine fauna such as the Paris Biota, as soon as the early Spathian, indicates that the post-PTB biotic recovery and the installation of complex ecosystems probably took place earlier than often assumed, at least at a regional scale.

Latest Smithian Ammonoids in northern Utah

Corroborating the existence of a UAZ6 (Unitary Association Zone, a means of biostratigraphic correlation).  See the paper linked below.  Characterized by the ammonoid Psudosageceras augustum (Brayard & Bucher, 2008) in association with Xenoceltites subevolutus Spath 1930. Found in rocks previously assigned to the Induan (lower Lower Triassic) Dinwoody Fm., now assigned to the Olenekian (upper Lower Triassic, top of Smithian) Thaynes Group.

Pseudosageceras augustum left and Xenoceltites subevolutus right

Xenoceltites subevolutus left and Pseudosageceras augustum right

In press, Article in GEOBIOS

Available online 18 June 2021

Abstract

The late Smithian extinction represents a major event within the Early Triassic. This event generally corresponds to a succession of two and possibly three successively less diverse, cosmopolitan ammonoid assemblages, which when present, provide a robust biostratigraphic framework and precise correlations at different spatial scales. In the western USA basin, known occurrences of latest Smithian taxa are rare and until now, have only been documented from northeastern Nevada. Based on these restricted basinal occurrences, a regional zone representing the latest Smithian was postulated but not corroborated, as representative taxa had not yet been reported from outside Nevada. Here we document two new ammonoid assemblages from distant localities in northern Utah, overlying the late Smithian Anasibirites beds and characterized by the unambiguous co-occurrence of Xenoceltites subevolutus and Pseudosageceras augustum. The existence of a latest Smithian zone in the western USA basin is therefore validated, facilitating the identification of the Smithian/Spathian boundary and intra-basin correlation. This zone also correlates with the latest Smithian zone recognized from southern Tethyan basins. Additionally, these new data support other observed occurrences of Xenoceltites subevolutus throughout most of the late Smithian.

Dinwoody Ammonoids & Nautiloids

LATE GRIESBACHIAN (EARLY TRIASSIC) AMMONOIDS AND NAUTILOIDS FROM THE DINWOODY FORMATION AT CRITTENDEN SPRINGS, ELKO COUNTY, NEVADA

by

JAMES F. JENKS, TAKUMI MAEKAWA, DAVID WARE, YASUNARI SHIGETA, ARNAUD BRAYARD and KEVIN G. BYLUND

Abstract—We document a relatively small but very important late Griesbachian ammonoid and nautiloid assemblage from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada. This discovery represents the first significant report of late Griesbachian ammonoids in the low-paleolatitudes of eastern Panthalassa, and it also signifies the first report of Wordieoceras wordiei and two co-occurring taxa outside of the Boreal Realm. This similarity in ammonoid faunas, irrespective of paleolatitude, provides support for the concept of weak latitudinal diversity gradients following the end-Permian extinction. The finding is even more noteworthy given the Dinwoody Formation’s reputation for poor fossil preservation and a near complete absence of documented and identifiable ammonoid and nautiloid occurrences. Consisting of four taxa of which two are newly described, the ammonoid fauna includes Wordieoceras wordiei (Spath), Kyoktites cf. K. hebeiseni Ware and Bucher, Wordieoceras mullenae n. sp. and a new taxon belonging to the Mullericeratidae family, Ophimullericeras paullae n. gen., n. sp. The nautiloids are attributed to a newly described species, i.e., Xiaohenautilus mulleni n. sp., a genus heretofore unknown in eastern Panthalassa but commonly reported from the late Griesbachian of South Primorye and the late Griesbachian/early Dienerian of South China.

New Mexico Museum of Natural History & Science Bulletin 86

Paris Biota Ammonoids & Nautiloids

 A very late post

Ammonoids and nautiloids from the earliest Spathian Paris Biota and other early Spathian localities in southeastern Idaho, USA

Arnaud Brayard, James F. Jenks, Kevin G.Bylund and the Paris Biota Team 2019

Part of a Special Volume dedicated to the Paris Biota of SE Idaho.

Some Prionitids Lumped

With a few very narrowly defined species, The Prionitidae is a family of very closely related ammonoids.  However most collections, especially from the western US, always contained "Prionitid" or "Prionitid indet.", Prionitids with bullae or ribs, maybe nodes or tubercles, that just didn't fit with any of the other described genera or species.  With new collections from the Smithian (Early Triassic) Sinbad Formation around the Utah/Arizona border, we were able to synonymize all these with ammonoids described in 1929 by Asa Mathews.  By priority, Gurleyites smithi Mathews 1929 replaces Arctoprionites resseri (Mathews 1929).  With a very wide range of intraspecific variation, the new taxon will fit just about anything that doesn't fit in one of the other defined taxa.

See our new paper here.

New middle and late Smithian ammonoid faunas from the Utah/Arizona border: New evidence for calibrating Early Triassic transgressive-regressive trends and paleobiogeographical signals in the western USA basin

 

 

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

Another Payday

Meekoceras bylundi Jenks & Brayard 2018
Holotype

A little late, but...

https://albertiana-sts.org/2018/01/08/publication-announcement-smithian-early-triassic-ammonoids-from-crittenden-springs-elko-county-nevada/

Thank you Jim and Arnaud!