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1. Fossil eggshell diversity of the Mussentuchit Member, Cedar Mountain Formation, Utah

   https://doi.org/10.1371/journal.pone.0314689  

   Hedge, Joshua; Tucker, Ryan T; Makovicky, Peter J; Zanno, Lindsay E (February 2025, PLOS ONE)

   Claessens, Leon (Ed.)

   The first fossil eggshell from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation was described over fifty years ago. In the half-century since, oodiversity of this rock unit has been limited to a single, taxonomically unstable ootaxon, currently formulated asMacroelongatoolithus carlylei. Recently, there has been a renewed effort to recover and describe the macrofauna of the Mussentuchit; however, these advances are limited to the body fossil record. Here, we examine the range of eggshells present in the Mussentuchit Member and assess the preserved biodiversity they represent. Gross morphological and microstructural inspection reveals a greater diversity of eggshells than previously described. We identify six ootaxa: three Elongatoolithidae oogenera (Macroelongatoolithus,Undulatoolithus,Continuoolithus), eggs laid by oviraptorosaur dinosaurs; two oospecies ofSpheroolithuslaid by ornithopod dinosaurs; andMycomorphoolithus kohringi, laid by a crocodylomorph. The diversity of Elongatoolithidae in the Mussentuchit requires a co-occurrence of at least three putative oviraptorosaurs, the oldest such phenomenon in North America. The occurrence of the crocodylomorph oogenusMycomorphoolithusis the first recognized occurrence outside of Europe, and the youngest yet documented. This new ooassemblage is more representative of the known paleobiodiversity of Cenomanian-age strata of Western North America and complements the body fossil record in improving our understanding of this crucial—yet poorly documented—timeslice within the broader evolution of the Cretaceous Western Interior Basin. 

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2. Paralic sedimentology of the Mussentuchit Member coastal plain, Cedar Mountain Formation, central Utah, U.S.A.

   https://doi.org/10.2110/jsr.2021.028  

   Tucker, Ryan T.; Suarez, Celina A.; Makovicky, Peter J.; Zanno, Lindsay E. (June 2022, Journal of Sedimentary Research)

   ABSTRACT Although intensified work on the volcaniclastic-rich sediments of the fossil-bearing Mussentuchit Member (uppermost Cedar Mountain Formation, Utah) has provided a refined chronostratigraphic framework, paleoenvironmental interpretations remain cryptic. To resolve this, we performed facies analysis and architectural reconstruction on exposed Mussentuchit Member outcrops south of Emery, central Utah, USA. Contrary to previous interpretations (fluvial, lacustrine), we identified a broad suite of facies that indicate that deposition occurred on the landward part of a paralic depocenter, influenced by both distal alluvial and proximal coastal systems. We conclude that the Mussentuchit Member was a sink for suspension-settling fines with most undergoing pedogenic alteration, analogous to the modern coastal plain of French Guiana (Wang et al. 2002; Anthony et al. 2010, 2014). However, this landward paralic depocenter was not uniform through time. Sedimentological evidence indicates landscape modification was ongoing, influenced by an altered base-level (high groundwater table, long residency of water in sediments, shifts in paleosol types, heavier to lighter δ18O, and distinct shifts in relative humidity (ε); common in coastal settings). If the above data is coupled with recent age data, we interpret that the Mussentuchit Member correlates to the S.B. 4 Greenhorn Regression (Thatcher Limestone) of the adjacent Western Interior Seaway to the east. As a landward paralic depocenter, the Mussentuchit would have been sensitive to base-level conditions in response to ongoing tectonic processes pushing the foredeep east, and lower paleo-CO2 levels coupled with a minor global sea-level fall (brief glacial phase) just before to the Cenomanian–Turonian Thermal Maximum. Altogether, our results not only strengthen linkages in the central Western Interior Seaway, but simultaneously results in novel linkages to near-coeval paralic depocenters across mid-Cenomanian North America. 

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3. Ecological Revision Of The Early Cenomanian Mussentuchit Member, Cedar Mountain Formation, Central Utah (USA)

   Tucker, RT; Makovicky, PJ; Cifelli, R; Zanno, LE (May 2023, The Anatomical Record)
4. A new semi‐fossorial thescelosaurine dinosaur from the Cenomanian‐age Mussentuchit Member of the Cedar Mountain Formation, Utah

   https://doi.org/10.1002/ar.25505  

   Avrahami, Haviv_M; Makovicky, Peter_J; Tucker, Ryan_T; Zanno, Lindsay_E (July 2024, The Anatomical Record)

   Abstract Thescelosaurines are a group of early diverging, ornithischian dinosaurs notable for their conservative bauplans and mosaic of primitive features. Although abundant within the latest Cretaceous ecosystems of North America, their record is poor to absent in earlier assemblages, leaving a large gap in our understanding of their evolution, origins, and ecological roles. Here we report a new small bodied thescelosaurine—Fona herzogaegen. et sp. nov.—from the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA.Fona herzogaeis represented by multiple individuals, representing one of the most comprehensive skeletal assemblages of a small bodied, early diverging ornithischian described from North America to date. Phylogenetic analysis recoversFonaas the earliest member of Thescelosaurinae, minimally containingOryctodromeus, and all three species ofThescelosaurus, revealing the clade was well‐established in North America by as early as the Cenomanian, and distinct from, yet continental cohabitants with, their sister clade, Orodrominae. To date, orodromines and thescelosaurines have not been found together within a single North American ecosystem, suggesting different habitat preferences or competitive exclusion. Osteological observations reveal extensive intraspecific variation across cranial and postcranial elements, and a number of anatomical similarities withOryctodromeus, suggesting a shared semi‐fossorial lifestyle. 

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5. A new semi-fossorial thescelosaurine dinosaur from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, Utah

   Avrahami, Haviv M; Makovicky, Peter J; Tucker, Ryan T; Zanno, Lindsay E (May 2024, The anatomical record)