DOI: 10.5061/dryad.51c59zwjb
title: Mussentuchit member fossil eggshell light microscope photographs and corresponding metrics

description: 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 as
 Macroelongatoolithus 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 of Spheroolithus laid by
 ornithopod dinosaurs; and Mycomorphoolithus 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 oogenus Mycomorphoolithus is 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.
description: In this study, we examined all fossilized eggshells recovered
 from the Mussentuchit Member of the Cedar Mountain Formation and housed at
 the NCSM (n &gt; 2,500), plus additional loaned material from the OMNH
 (n &gt; 1,500), FMNH (n = 77), and BYU (n = 8), to extensively analyze
 ootaxonomic diversity across twenty localities.  NCSM and FMNH fragments
 from the Mussentuchit Member were collected between 2012 and 2022, and
 fragments and thin section slides loaned from BYU and the OMNH were
 collected by Jensen and Cifelli et al., respectively.
 We systematically categorized fragments of eggshell into
 ‘morphotypes’ based on external ornamentation patterns, and selected the
 highest quality samples (free of additional matrix, appropriately sized)
 for photography and consumptive sampling. Fragments selected were
 photographed with a Keyence VHX-7000 Digital Microscope before creating
 radial thin sections to assess microstructural features such as crystal
 arrangement, pore networks, the ML/CL boundary, and ML/CL thickness
 ratios. We encased fragments in epoxy resin, cut the resulting blocks
 using a Buehler IsoMet 1000 Precision Saw, and polished them using a
 Buehler MetaServ 250 Grinder/Polisher to a thickness of 80 μm. We analyzed
 finalized thin sections with a Nikon Eclipse Ci Pol light microscope (with
 attached DS-FI 2 camera) and the Keyence VHX-7000 Digital Microscope for
 microstructure. Measurements of TST, ML and CL features were taken
 digitally using ImageJ. Further analysis of microstructure and
 ultrastructure, with a focus on crystal splaying across the ML/CL
 boundary, was undertaken on a Hitachi SU8700 field-emission scanning
 electron microscope at the NCSU Analytical Instrumentation Facility. We
 viewed samples at 100x magnification at variable pressure, with a 50 Pa
 backfill of dry nitrogen and a 20 kV accelerating voltage. These combined
 analyses were used to determine ootaxonomic assignment.
 Photographs included herein are from the microscope cameras and
 were not included in the manuscript. The images were used in
 correpsondence with ImageJ to collect quantitative and qualitative
 eggshell data (the csv file).
description: # Mussentuchit member fossil eggshell light microscope photographs and
 corresponding metrics 
 [https://doi.org/10.5061/dryad.51c59zwjb](https://doi.org/10.5061/dryad.51c59zwjb) ## Description of the data and file structure These data were collected as part of a study to assess the diversity of the eggshell assemblage of the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation in Emery County, Utah. ### Files and variables #### File: Mussentuchit\_Egg\_Cross\_Sections.zip **Description:** Images of the eggshells used in this study in radial cross section under both plane- and cross-polarized light #### File: Mussentuchit\_Egg\_Fragments\_Photographs.zip **Description:** Images of the fragments used in this study. There are images of both the surfaces of the eggs and then in cross section at two magnifications. #### File: Mussentuchit\_Eggshell\_Thin\_Section\_Matrix.csv **Description:** Final matrix assembled to assess quantitative and qualitative values for the eggshell fragments studied. ##### Variables * Specimen: accessioned specimen number * Slide Number: multiple slides sometimes taken from same fragment for thin sections. The number given is which of these were used. * Max. Thickness/mm: highest thickness of the eggshell in radial view, including ornamentation (measured in ImageJ.) * Min. Thickness/mm: lowest thickness of the eggshell in radial view (measured in ImageJ.) * Mean Thickness/mm: mean thickness of the eggshell in radial view, including ornamentation (measured in ImageJ.) * Shell Thickness Range/mm: thickness range of the eggshell in radial view, including ornamentation (measured in ImageJ.) * Thickness Variation %: range of thickness variation as a percentage. * Max Ornamentation Height/mm: highest thickness of the eggshell ornamentation in radial view (measured in ImageJ.) N/A if ornamentation not present or incomplete. * Ornamentation %: mean percentage of eggshell in radial view that was ornamentation. N/A if ornamentation not present or incomplete * Max. CL Thickness/mm: highest thickness of the continuous (crystal) layer of the eggshell in radial view (measured in ImageJ.) * Min. CL Thickness/mm: lowest thickness of the continuous (crystal) layer of the eggshell in radial view (measured in ImageJ.) * Mean CL Thickness/mm: mean thickness of the continuous (crystal) layer of the eggshell in radial view (measured in ImageJ.) * Max. ML Thickness/mm: highest thickness of the mammillary layer of the eggshell in radial view (measured in ImageJ.) * Min. ML Thickness/mm: lowest thickness of the mammillary layer of the eggshell in radial view (measured in ImageJ.) * Mean ML Thickness/mm: mean thickness of the mammillary layer of the eggshell in radial view. N/A if ML incomplete * Undulation %: percentage of variation in layer differences based on the undulating contact of the mammillary and continuous layers of the eggshell. N/A if ML incomplete * Max. ML:CL: highest ratio of the ML and CL of the eggshell in radial view. N/A if ML incomplete * Min. CL:ML: lowest ratio of the ML and CL of the eggshell in radial view. N/A if ML incomplete * CL:ML Range: ratio range of the ML and CL of the eggshell in radial view. N/A if ML incomplete * Mean CL:ML: average ratio of the ML and CL of the eggshell in radial view. N/A if ML incomplete * Mean Round ML:CL: average ratio of the ML and CL of the eggshell in radial view, rounded to the nearest 0.5 value. N/A if ML incomplete * Pore Canals: qualitative category of the pore system for the eggshell, *sensu *Carpenter (1999). N/A if pores not present. * Locality: Name of the Quarry at which the eggshell was found * Coordinates: latitude and longitude  of the eggshell locality * ML:CL Boundary: description of the contact between the two eggshell layers * Crystal Splaying (P/A): presence or absence of crystal splaying across the ML/CL boundary * Primary Ornamentation: qualitative category for the primary external sculpturing of the eggshell,* sensu *Carpenter (1999). '?' if ornamentation unclear/not befitting of the categories. * Secondary Ornamentation: qualitative category for the secondary external sculpturing of the eggshell if present,* sensu *Carpenter (1999). '?' if ornamentation unclear/not befitting of the categories. * Oofamily: Parataxonomic designation of the fragment at the oofamily level. * Oogenus: Parataxonomic designation of the fragment at the oogenus level. * Oospecies: Parataxonomic designation of the fragment at the oospecies level. * Notes: any additional notes about the eggshell (preservation etc.)