Morrison Formation: Enigmatic ornithopod specimens from Simon Quarry, Wyoming + modified bone material from Colorado and Wyoming (free pdfs)
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Ben Creisler
Jan 29, 2026, 1:09:17 AM (5 days ago) Jan 29
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Ben Creisler
More Morrison Formation papers with free pdfs:
L. J. Krumenacker, Robert J. Gay, Joseph E. Peterson, Rod Scheetz, and Robert Simon (2026)
Enigmatic ornithopod specimens from the Simon Quarry of the Late Jurassic Morrison Formation, Bighorn Basin, Wyoming
In: Foster et al., 2026, New Developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 102: 319-329
https://www.academia.edu/149123555/ENIGMATIC_ORNITHOPOD_SPECIMENS_FROM_THE_SIMON_QUARRY_OF_THE_LATE_JURASSIC_MORRISON_FORMATION_BIGHORN_BASIN_WYOMING
Iguanodontian ornithopods described from the Morrison Formation comprise Dryosaurus and Camptosaurus, both of which have two species within their respective genera. Here we describe three iguanodontian specimens from the Simon Quarry (Red Canyon Ranch Quarry) of the Bighorn Basin, near Shell, Wyoming. Based on their morphological disparities from Camptosaurus and Dryosaurus we hypothesize the possible presence of undescribed ornithopod(s) from the Morrison Formation of the Bighorn Basin. These specimens include a braincase (IMNH 2806/54191), a left metatarsal (IMNH 2806/54302), and a skull (NMZ 1000265). IMNH 54191 possesses a feature previously undescribed among archosauria consisting of a posteroventrally projecting bilobate prong that extends from the basisphenoid. Preliminary observations indicate its apparent absence among other taxa is due to taphonomy and lack of description, but this hypothesis needs further testing. The left metatarsal (IMNH 2806/54302) exhibits a distinct morphology including a distinct medial sulcus not known among other dinosaurs, and a condylar cap, and suggests the presence of a more gracile footed as-yet unrecognized ornithopod taxon similar to Camptosaurus and Dryosaurus, with a size similar to the former. NMZ 1000265, a fairly complete skull, exhibits a suite of characters such as elongate maxillae and dentaries, a triangular parietal that tapers posteriorly, and a triangular lateral fenestra that suggest this specimen is distinct from Camptosaurus and Dryosaurus. Though this hypothesis needs further testing. The possible presence of a new iguanodontian taxon in the northern exposures of the Morrison Formation mirrors the emerging pattern of new sauropod and basal neornithischian diversity within the Morrison depositional basin. This pattern also suggests the possible presence of additional ornithischian and saurischian taxa that are currently unknown and unrecognized in the Morrison Formation. Continued study of the hypotheses posed here could provide additional data on the diversification of dinosaurian taxa before the incursion of the Western Interior Seaway and the onset of Early Cretaceous dinosaurian faunas.
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Julia McHugh and Stephanie K. Drumheller (2026)
Inter-site and inter-analyst variation in reported frequencies of modified bone material from the Upper Jurassic Morrison Formation of Colorado and Wyoming
In: Foster et al., 2026, New Developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 102: 375-385
https://www.researchgate.net/publication/400052640_INTER-SITE_AND_INTER-ANALYST_VARIATION_IN_REPORTED_FREQUENCIES_OF_MODIFIED_BONE_MATERIAL_FROM_THE_UPPER_JURASSIC_MORRISON_FORMATION_OF_COLORADO_AND_WYOMING
Bone surface modifications (BSMs) on vertebrate remains can provide critical data on taphonomic and paleoecologic activity. Here, we present the results of a BSM survey of fossil material from Bone Cabin Quarry (BCQ) (Morrison Formation) housed at the Museums of Western Colorado. Frequencies of BSMs were calculated using two metrics: 1) percentage of altered elements, and 2) percentage of altered surface area, which allowed us to compare specimens and samples that vary in size, shape, completeness, and/or field collection technique. Results from this survey were then compared to a recent large-scale analysis of BSM data from the Mygatt-Moore Quarry (MMQ) in Colorado (Morrison Formation) previously conducted by these authors. Results show a higher overall frequency of BSMs among affected surface area in the MMQ sample than BCQ. This is echoed by a lower frequency of modified elements in the BCQ survey. However, when parsed between vertebrate and invertebrate trace makers the amount of invertebrate activity was nearly identical between MMQ and BCQ, while the frequencies of vertebrate marks are significantly lower at BCQ, as calculated through both metrics. The disparity of BSM frequencies, and thus inferred taphonomic activity, at the two Morrison sites may be due to differences in local ecologies rather than differences in carcass residence times due to disparate depositional regimes. Lithologies with larger grain sizes are often interpreted as having more rapid burial and thus lower rates of taphonomic activity. This study shows that systems are far more complex, and grain size may be a poor indicator of predicted BSM frequency. Broadening comparisons to surveys of Morrison material conducted by other research groups further highlights the complications of drawing biologically meaningful conclusions between datasets derived using different analytical methods to address varying research goals. This study illustrates a need for care in these types of inter-site comparisons to ensure the underlying data are equivalently collected and sufficiently parsed prior to attempting broad paleoecological or taphonomic interpretations.
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Free pdf:
L. J. Krumenacker, Robert J. Gay, Joseph E. Peterson, Rod Scheetz, and Robert Simon (2026)
Enigmatic ornithopod specimens from the Simon Quarry of the Late Jurassic Morrison Formation, Bighorn Basin, Wyoming
In: Foster et al., 2026, New Developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 102: 319-329
https://www.academia.edu/149123555/ENIGMATIC_ORNITHOPOD_SPECIMENS_FROM_THE_SIMON_QUARRY_OF_THE_LATE_JURASSIC_MORRISON_FORMATION_BIGHORN_BASIN_WYOMING
Iguanodontian ornithopods described from the Morrison Formation comprise Dryosaurus and Camptosaurus, both of which have two species within their respective genera. Here we describe three iguanodontian specimens from the Simon Quarry (Red Canyon Ranch Quarry) of the Bighorn Basin, near Shell, Wyoming. Based on their morphological disparities from Camptosaurus and Dryosaurus we hypothesize the possible presence of undescribed ornithopod(s) from the Morrison Formation of the Bighorn Basin. These specimens include a braincase (IMNH 2806/54191), a left metatarsal (IMNH 2806/54302), and a skull (NMZ 1000265). IMNH 54191 possesses a feature previously undescribed among archosauria consisting of a posteroventrally projecting bilobate prong that extends from the basisphenoid. Preliminary observations indicate its apparent absence among other taxa is due to taphonomy and lack of description, but this hypothesis needs further testing. The left metatarsal (IMNH 2806/54302) exhibits a distinct morphology including a distinct medial sulcus not known among other dinosaurs, and a condylar cap, and suggests the presence of a more gracile footed as-yet unrecognized ornithopod taxon similar to Camptosaurus and Dryosaurus, with a size similar to the former. NMZ 1000265, a fairly complete skull, exhibits a suite of characters such as elongate maxillae and dentaries, a triangular parietal that tapers posteriorly, and a triangular lateral fenestra that suggest this specimen is distinct from Camptosaurus and Dryosaurus. Though this hypothesis needs further testing. The possible presence of a new iguanodontian taxon in the northern exposures of the Morrison Formation mirrors the emerging pattern of new sauropod and basal neornithischian diversity within the Morrison depositional basin. This pattern also suggests the possible presence of additional ornithischian and saurischian taxa that are currently unknown and unrecognized in the Morrison Formation. Continued study of the hypotheses posed here could provide additional data on the diversification of dinosaurian taxa before the incursion of the Western Interior Seaway and the onset of Early Cretaceous dinosaurian faunas.
=====
Julia McHugh and Stephanie K. Drumheller (2026)
Inter-site and inter-analyst variation in reported frequencies of modified bone material from the Upper Jurassic Morrison Formation of Colorado and Wyoming
In: Foster et al., 2026, New Developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 102: 375-385
https://www.researchgate.net/publication/400052640_INTER-SITE_AND_INTER-ANALYST_VARIATION_IN_REPORTED_FREQUENCIES_OF_MODIFIED_BONE_MATERIAL_FROM_THE_UPPER_JURASSIC_MORRISON_FORMATION_OF_COLORADO_AND_WYOMING
Bone surface modifications (BSMs) on vertebrate remains can provide critical data on taphonomic and paleoecologic activity. Here, we present the results of a BSM survey of fossil material from Bone Cabin Quarry (BCQ) (Morrison Formation) housed at the Museums of Western Colorado. Frequencies of BSMs were calculated using two metrics: 1) percentage of altered elements, and 2) percentage of altered surface area, which allowed us to compare specimens and samples that vary in size, shape, completeness, and/or field collection technique. Results from this survey were then compared to a recent large-scale analysis of BSM data from the Mygatt-Moore Quarry (MMQ) in Colorado (Morrison Formation) previously conducted by these authors. Results show a higher overall frequency of BSMs among affected surface area in the MMQ sample than BCQ. This is echoed by a lower frequency of modified elements in the BCQ survey. However, when parsed between vertebrate and invertebrate trace makers the amount of invertebrate activity was nearly identical between MMQ and BCQ, while the frequencies of vertebrate marks are significantly lower at BCQ, as calculated through both metrics. The disparity of BSM frequencies, and thus inferred taphonomic activity, at the two Morrison sites may be due to differences in local ecologies rather than differences in carcass residence times due to disparate depositional regimes. Lithologies with larger grain sizes are often interpreted as having more rapid burial and thus lower rates of taphonomic activity. This study shows that systems are far more complex, and grain size may be a poor indicator of predicted BSM frequency. Broadening comparisons to surveys of Morrison material conducted by other research groups further highlights the complications of drawing biologically meaningful conclusions between datasets derived using different analytical methods to address varying research goals. This study illustrates a need for care in these types of inter-site comparisons to ensure the underlying data are equivalently collected and sufficiently parsed prior to attempting broad paleoecological or taphonomic interpretations.
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