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