Marmoretta drescherae, new reptile species from Portugal + Oldman-Dinosaur Park Formation dinosaur biostratigraphy + Eastern Gobi Basin Cretaceous fossil-bearing units
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Ben Creisler
Mar 14, 2025, 2:28:53 PMMar 14
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Ben Creisler
Alexandre R.D. Guillaume, Eduardo Puértolas-Pascual, and Miguel Moreno-Azanza (2025)
Revisiting the choristodere and stem-lepidosaur specimens of the Guimarota Beds (Kimmeridgian, Portugal): taxonomic implications
Acta Palaeontologica Polonica 70(1): 77-96
doi:10.4202/app.01202.2024
https://www.app.pan.pl/article/item/app012022024.html
The Guimarota beds (Kimmeridgian, Portugal) constitute one of the richest microvertebrate assemblages for the Upper Jurassic, which include a diverse fauna of small reptiles. Among others, was described a new species of a small choristodere, “Cteniogenys reedi”. The genus, also known from the Morrison Formation (Upper Jurassic, USA) and the Kirtlington Mammal Bed (Middle Jurassic, UK), constitutes one of the oldest and most basal forms of this aquatic reptile lineage considered to be ecologically similar to crocodylomorphs. However, later works considered this species to be a junior synonym, and challenged the assignment of some of this material, ascribing them to the aquatic stem-lepidosaur Marmoretta. Here, we provided a revision of the published material from the Guimarota beds assigned to Cteniogenys, together with unreported and mislabelled specimens. We confirmed that the Portuguese specimens are probably non-conspecific with the taxa described in the Upper Jurassic of North America and in the Middle Jurassic of England. Unfortunately, the lack of diagnostic features from the only valid species prevented to confirm the original description as a distinct new species. Therefore, we only referred it to Cteniogenys aff. C. antiquus. We further supported the presence of Marmoretta in the Upper Jurassic of Portugal, and erected a new species, Marmoretta drescherae. Those occurrences support original palaeoenvironmental interpretations of the Guimarota beds as a wetland, probably close to mangrove-like, with important freshwater inputs. The presence of Cteniogenys in Portugal further supports faunal interchanges between North America, Europe, and potentially Northwestern Africa during the Jurassic/Cretaceous transition, if later occurrences are to be confirmed. The presence of Marmoretta also extend the temporal range of this relict reptile lineage at a time where squamates were radiating. However, its absence in other contemporary Jurassic localities, notably in the Lourinhã and Morrison formations, could hint towards ecological differences between those assemblages.
======
Alexandre V. Demers-Potvin and Hans C.E. Larsson (2025)
High local variability in elevation of the Oldman-Dinosaur Park Formation contact revealed by digital outcrop reconstruction, and implications for dinosaur biostratigraphy of the Late Cretaceous (Campanian) Belly River Group of Alberta, Canada.
Palaeontologia Electronica 28(1): a13.
doi: https://doi.org/10.26879/1447
https://palaeo-electronica.org/content/2025/5473-dinosaur-park-bonebed-3d-model
The Late Cretaceous (Campanian) Belly River Group of Dinosaur Provincial Park (DPP), Alberta, Canada, combines the world’s most complete dinosaur chronofauna with precise and accurate absolute age constraints obtained from ashfall deposits. However, the time-averaging of individual fossil quarries caused by their preservation in fluvio-deltaic depositional environments implies significant uncertainties on their relative age and by extension on our knowledge of local palaeodiversity patterns. The biostratigraphic position of a multigeneric bonebed at a transitional period between successive dinosaur assemblage zones, combined with its proximity to an exposure of the Oldman-Dinosaur Park Formation (OF-DPF) contact, provides an ideal study system for such an investigation. Images acquired with an unmanned aerial vehicle (UAV) were aligned by structure-from-motion (SfM) photogrammetry to construct a 3-D digital outcrop model (DOM), a digital elevation model (DEM), and an orthomosaic of the 0.446 km2 area surrounding the bonebed. The first key result is that the absolute elevation of the OF-DPF contact varies by ~12 m locally, which causes hitherto underestimated uncertainties on any fossil locality’s stratigraphic height relative to it. Moreover, we find that the lower DPF has the potential to be locally subdivided into at least three successive channel cut-and-fill rhythms, some of which are promising candidate marker beds for a more expansive correlation of DPP’s fossil heritage. This study shows how rapidly developing UAV-based geological mapping methods contribute to exploring stratigraphic successions in other fossil-rich regions on a larger scale than what is currently possible from ground-based surveys alone.
Jesse Benjamin van Niekerk, Ryan T. Tucker, Puntsag Delgerzaya, William J. Freimuth, Tsogtbaatar Chinzorig, Khishigjav Tsogtbaatar, Junki Yoshida & Lindsay E. Zanno (2025)
Geological reassessment of syn-rift extensional sequences in the Shine Usny Tolgod and Dzun Shakhai fossil localities, Eastern Gobi Basin, Mongolia
Sedimentology (advance online publication)
doi: https://doi.org/10.1111/sed.70003
https://onlinelibrary.wiley.com/doi/10.1111/sed.70003
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/sed.70003
Sedimentary infill patterns in the Eastern Gobi Basin of southern Mongolia record a complex, polyphased history. Asynchronous timing and intensities of extensional tectonism during the Early Cretaceous fragmented the Eastern Gobi Basin into a series of sub-basins within an extensional rift (horst-graben) setting, which likely infilled penecontemporaneously to asynchronously. Of these sub-basins, the north-eastern Sainshand sub-basin preserves a nearly continuous Lower Cretaceous syn-rift succession. However, many outstanding uncertainties concerning intra-sub-basinal and inter-sub-basinal biostratigraphic correlations persist, including stratigraphic linkages locally at the Dzun Shakhai and Shine Usny Tolgod localities, regionally across the eastern Sainshand sub-basin, along with the adjacent Zuunbayan and Unegt sub-basins. This study confirms that Dzun Shakhai and Shine Usny Tolgod are hosted within a horst-graben setting with sedimentary successions composed of locally sourced (para-autochthonous to autochthonous) detritus. Facies analysis reveals a broad suite of evolving transitional depositional environments, including alluvial, fluvial and lacustrine environments. Basin infill initiated in a retrogradational setting (underfilled-starved stage) that transitioned to an aggradational and a subsequent progradational setting (filled stage). Based on the identification of six syn-rift sequence boundaries (SR1 to SR6), this study determined that this portion of the Sainshand sub-basin fits a gradual subsidence model. Additionally, this study presents significant sedimentological evidence for: (i) the designation of a new member, the Ikh Ulaan Nuur Member of the Shinekhudag Formation; and (ii) the subdivision of the Khukhteeg Formation into an informal lower and upper member. These novel sedimentological data improve lithostratigraphic and palaeoenvironmental correlations across the Sainshand sub-basin, with strengthened correlations to the adjacent Zuunbayan and Unegt sub-basins and more peripheral linkages to the Erlian, Yingen and Songliao basins of north-eastern China. These findings provide an important foundation for assessing the spatiotemporal distribution of syn-rift fossil-bearing units across the greater Eastern Gobi Basin and the North China Block.
New papers:
Marmoretta drescherae sp. nov.
Alexandre R.D. Guillaume, Eduardo Puértolas-Pascual, and Miguel Moreno-Azanza (2025)
Revisiting the choristodere and stem-lepidosaur specimens of the Guimarota Beds (Kimmeridgian, Portugal): taxonomic implications
Acta Palaeontologica Polonica 70(1): 77-96
doi:10.4202/app.01202.2024
https://www.app.pan.pl/article/item/app012022024.html
The Guimarota beds (Kimmeridgian, Portugal) constitute one of the richest microvertebrate assemblages for the Upper Jurassic, which include a diverse fauna of small reptiles. Among others, was described a new species of a small choristodere, “Cteniogenys reedi”. The genus, also known from the Morrison Formation (Upper Jurassic, USA) and the Kirtlington Mammal Bed (Middle Jurassic, UK), constitutes one of the oldest and most basal forms of this aquatic reptile lineage considered to be ecologically similar to crocodylomorphs. However, later works considered this species to be a junior synonym, and challenged the assignment of some of this material, ascribing them to the aquatic stem-lepidosaur Marmoretta. Here, we provided a revision of the published material from the Guimarota beds assigned to Cteniogenys, together with unreported and mislabelled specimens. We confirmed that the Portuguese specimens are probably non-conspecific with the taxa described in the Upper Jurassic of North America and in the Middle Jurassic of England. Unfortunately, the lack of diagnostic features from the only valid species prevented to confirm the original description as a distinct new species. Therefore, we only referred it to Cteniogenys aff. C. antiquus. We further supported the presence of Marmoretta in the Upper Jurassic of Portugal, and erected a new species, Marmoretta drescherae. Those occurrences support original palaeoenvironmental interpretations of the Guimarota beds as a wetland, probably close to mangrove-like, with important freshwater inputs. The presence of Cteniogenys in Portugal further supports faunal interchanges between North America, Europe, and potentially Northwestern Africa during the Jurassic/Cretaceous transition, if later occurrences are to be confirmed. The presence of Marmoretta also extend the temporal range of this relict reptile lineage at a time where squamates were radiating. However, its absence in other contemporary Jurassic localities, notably in the Lourinhã and Morrison formations, could hint towards ecological differences between those assemblages.
======
Free pdf:
Alexandre V. Demers-Potvin and Hans C.E. Larsson (2025)
High local variability in elevation of the Oldman-Dinosaur Park Formation contact revealed by digital outcrop reconstruction, and implications for dinosaur biostratigraphy of the Late Cretaceous (Campanian) Belly River Group of Alberta, Canada.
Palaeontologia Electronica 28(1): a13.
doi: https://doi.org/10.26879/1447
https://palaeo-electronica.org/content/2025/5473-dinosaur-park-bonebed-3d-model
The Late Cretaceous (Campanian) Belly River Group of Dinosaur Provincial Park (DPP), Alberta, Canada, combines the world’s most complete dinosaur chronofauna with precise and accurate absolute age constraints obtained from ashfall deposits. However, the time-averaging of individual fossil quarries caused by their preservation in fluvio-deltaic depositional environments implies significant uncertainties on their relative age and by extension on our knowledge of local palaeodiversity patterns. The biostratigraphic position of a multigeneric bonebed at a transitional period between successive dinosaur assemblage zones, combined with its proximity to an exposure of the Oldman-Dinosaur Park Formation (OF-DPF) contact, provides an ideal study system for such an investigation. Images acquired with an unmanned aerial vehicle (UAV) were aligned by structure-from-motion (SfM) photogrammetry to construct a 3-D digital outcrop model (DOM), a digital elevation model (DEM), and an orthomosaic of the 0.446 km2 area surrounding the bonebed. The first key result is that the absolute elevation of the OF-DPF contact varies by ~12 m locally, which causes hitherto underestimated uncertainties on any fossil locality’s stratigraphic height relative to it. Moreover, we find that the lower DPF has the potential to be locally subdivided into at least three successive channel cut-and-fill rhythms, some of which are promising candidate marker beds for a more expansive correlation of DPP’s fossil heritage. This study shows how rapidly developing UAV-based geological mapping methods contribute to exploring stratigraphic successions in other fossil-rich regions on a larger scale than what is currently possible from ground-based surveys alone.
====
Free pdf:
Jesse Benjamin van Niekerk, Ryan T. Tucker, Puntsag Delgerzaya, William J. Freimuth, Tsogtbaatar Chinzorig, Khishigjav Tsogtbaatar, Junki Yoshida & Lindsay E. Zanno (2025)
Geological reassessment of syn-rift extensional sequences in the Shine Usny Tolgod and Dzun Shakhai fossil localities, Eastern Gobi Basin, Mongolia
Sedimentology (advance online publication)
doi: https://doi.org/10.1111/sed.70003
https://onlinelibrary.wiley.com/doi/10.1111/sed.70003
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/sed.70003
Sedimentary infill patterns in the Eastern Gobi Basin of southern Mongolia record a complex, polyphased history. Asynchronous timing and intensities of extensional tectonism during the Early Cretaceous fragmented the Eastern Gobi Basin into a series of sub-basins within an extensional rift (horst-graben) setting, which likely infilled penecontemporaneously to asynchronously. Of these sub-basins, the north-eastern Sainshand sub-basin preserves a nearly continuous Lower Cretaceous syn-rift succession. However, many outstanding uncertainties concerning intra-sub-basinal and inter-sub-basinal biostratigraphic correlations persist, including stratigraphic linkages locally at the Dzun Shakhai and Shine Usny Tolgod localities, regionally across the eastern Sainshand sub-basin, along with the adjacent Zuunbayan and Unegt sub-basins. This study confirms that Dzun Shakhai and Shine Usny Tolgod are hosted within a horst-graben setting with sedimentary successions composed of locally sourced (para-autochthonous to autochthonous) detritus. Facies analysis reveals a broad suite of evolving transitional depositional environments, including alluvial, fluvial and lacustrine environments. Basin infill initiated in a retrogradational setting (underfilled-starved stage) that transitioned to an aggradational and a subsequent progradational setting (filled stage). Based on the identification of six syn-rift sequence boundaries (SR1 to SR6), this study determined that this portion of the Sainshand sub-basin fits a gradual subsidence model. Additionally, this study presents significant sedimentological evidence for: (i) the designation of a new member, the Ikh Ulaan Nuur Member of the Shinekhudag Formation; and (ii) the subdivision of the Khukhteeg Formation into an informal lower and upper member. These novel sedimentological data improve lithostratigraphic and palaeoenvironmental correlations across the Sainshand sub-basin, with strengthened correlations to the adjacent Zuunbayan and Unegt sub-basins and more peripheral linkages to the Erlian, Yingen and Songliao basins of north-eastern China. These findings provide an important foundation for assessing the spatiotemporal distribution of syn-rift fossil-bearing units across the greater Eastern Gobi Basin and the North China Block.
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