Helopanoplia and pan-trionychid turtles from Late Cretaceous Lance and Hell Creek formations + Triassic Rhaetian bone bed in Northern Switzerland (free pdfs)
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Ben Creisler
Jun 3, 2026, 5:24:14 PM (2 days ago) Jun 3
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Ben Creisler
New papers:
Bone beds represent key archives for reconstructing coastal ecosystems, yet their depositional environments are often debated. Here we present an integrated sedimentological, palaeontological, ichnological, palynological and geochemical study of the Late Triassic Niederschönthal bone bed (Belchen Member, Klettgau Formation) in northern Switzerland. The bone bed occurs as a thin, laterally discontinuous conglomeratic layer resting on an erosive surface. It is dominated by coprolites, vertebrate remains, reworked lithoclasts and micritic pebbles. The vertebrate assemblage is diverse and dominated by osteichthyans and chondrichthyans, with subordinate phytosaurs and temnospondyl amphibians, alongside abundant charcoal and plant debris. Sedimentological features, including bored micritic pebbles with pyrite-rich rims, combined with stable isotope data, indicate deposition under sulfate-rich, at least polyhaline conditions. Palynological assemblages dominated by hygrophilous spores and characteristic Rhaetian dinoflagellates constrain the age to the middle Rhaetian and document a diverse lowland vegetation adapted to a humid environment. The faunal composition, coprolite assemblage and sedimentary structures point to repeated reworking and concentration of vertebrate remains during short-lived high-energy events. We interpret the Niederschönthal bone bed as having formed in a muddy coastal plain to lagoonal environment with fluvial-estuarine to marine channels having been periodically affected by small-scale transgressive pulses. This study reconciles earlier conflicting interpretations by demonstrating that the bone bed records a complex interplay of terrestrial, freshwater and marine influences rather than a fully marine or purely continental setting.
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Free pdf:
Walter G. Joyce, Léa C. Girard & Tyler R. Lyson (2026)
A reassessment of the latest Cretaceous (Maastrichtian) pan-trionychid turtle Helopanoplia beecheri comb. nov.
Swiss Journal of Palaeontology 145: 665-677
doi: https://doi.org/10.3897/sjp.145.189487
https://sjp.pensoft.net/article/189487/
The pan-trionychids Aspideretes beecheri and Helopanoplia distincta were named at the beginning of the 20th century based on fossils collected from the Late Cretaceous (Maastrichtian) Lance Formation of Wyoming. Interestingly, even though numerous additional pan-trionychid remains from Late Cretaceous formations of the Upper Great Plains have since been referred to Helopanoplia distincta based on its unique surface texture, no additional specimens have been referred to Aspideretes beecheri. We figure and describe all material previously referred to Aspideretes beecheri and select specimens referred to Helopanoplia distincta. Interspecific and intraspecific variation is assessed by reference to extant trionychids as a basis for taxonomic revision. We re-assign all specimens historically referred to Aspideretes beecheri to Axestemys splendidus and Axestemys infernalis. An unusual plastron previously thought to represent Helopanoplia distincta is referred to Hutchemys walkerorum. Although the type of Helopanoplia distincta is characterized by a distinct, tuberculate shell surface texture, material previously referred to this taxon suggests that this texture is only occasionally found in some parts of the shell. The holotype of Aspideretes beecheri otherwise shows characteristics consistent with being the subadult of material previously referred to Helopanoplia distincta. We thus conclude that the two taxa are synonymous and form the new combination Helopanoplia beecheri. We urge caution when identifying fragmentary pan-trionychid remains, as a tuberculate surface texture pattern is found in at least two distinct taxa. We support the conclusion, nonetheless, that Helopanoplia beecheri is one of only a few turtles to have gone extinct at the Cretaceous–Paleogene boundary.
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Free pdf:
Christian Andreas Meyer, Andreas Wetzel, Guido Roghi & Evelyn Kustatscher (2027)
Sedimentology and palaeoecology of a Rhaetian bone bed in Northern Switzerland formed during transgression of a muddy coastal plain setting with fluvial-estuarine channels.
Swiss Journal of Geosciences 119: 85-110
doi: https://doi.org/10.3897/sjg.119.187486
https://sjg.pensoft.net/article/187486/list/9/
Walter G. Joyce, Léa C. Girard & Tyler R. Lyson (2026)
A reassessment of the latest Cretaceous (Maastrichtian) pan-trionychid turtle Helopanoplia beecheri comb. nov.
Swiss Journal of Palaeontology 145: 665-677
doi: https://doi.org/10.3897/sjp.145.189487
https://sjp.pensoft.net/article/189487/
The pan-trionychids Aspideretes beecheri and Helopanoplia distincta were named at the beginning of the 20th century based on fossils collected from the Late Cretaceous (Maastrichtian) Lance Formation of Wyoming. Interestingly, even though numerous additional pan-trionychid remains from Late Cretaceous formations of the Upper Great Plains have since been referred to Helopanoplia distincta based on its unique surface texture, no additional specimens have been referred to Aspideretes beecheri. We figure and describe all material previously referred to Aspideretes beecheri and select specimens referred to Helopanoplia distincta. Interspecific and intraspecific variation is assessed by reference to extant trionychids as a basis for taxonomic revision. We re-assign all specimens historically referred to Aspideretes beecheri to Axestemys splendidus and Axestemys infernalis. An unusual plastron previously thought to represent Helopanoplia distincta is referred to Hutchemys walkerorum. Although the type of Helopanoplia distincta is characterized by a distinct, tuberculate shell surface texture, material previously referred to this taxon suggests that this texture is only occasionally found in some parts of the shell. The holotype of Aspideretes beecheri otherwise shows characteristics consistent with being the subadult of material previously referred to Helopanoplia distincta. We thus conclude that the two taxa are synonymous and form the new combination Helopanoplia beecheri. We urge caution when identifying fragmentary pan-trionychid remains, as a tuberculate surface texture pattern is found in at least two distinct taxa. We support the conclusion, nonetheless, that Helopanoplia beecheri is one of only a few turtles to have gone extinct at the Cretaceous–Paleogene boundary.
=====
Free pdf:
Christian Andreas Meyer, Andreas Wetzel, Guido Roghi & Evelyn Kustatscher (2027)
Sedimentology and palaeoecology of a Rhaetian bone bed in Northern Switzerland formed during transgression of a muddy coastal plain setting with fluvial-estuarine channels.
Swiss Journal of Geosciences 119: 85-110
doi: https://doi.org/10.3897/sjg.119.187486
https://sjg.pensoft.net/article/187486/list/9/
Bone beds represent key archives for reconstructing coastal ecosystems, yet their depositional environments are often debated. Here we present an integrated sedimentological, palaeontological, ichnological, palynological and geochemical study of the Late Triassic Niederschönthal bone bed (Belchen Member, Klettgau Formation) in northern Switzerland. The bone bed occurs as a thin, laterally discontinuous conglomeratic layer resting on an erosive surface. It is dominated by coprolites, vertebrate remains, reworked lithoclasts and micritic pebbles. The vertebrate assemblage is diverse and dominated by osteichthyans and chondrichthyans, with subordinate phytosaurs and temnospondyl amphibians, alongside abundant charcoal and plant debris. Sedimentological features, including bored micritic pebbles with pyrite-rich rims, combined with stable isotope data, indicate deposition under sulfate-rich, at least polyhaline conditions. Palynological assemblages dominated by hygrophilous spores and characteristic Rhaetian dinoflagellates constrain the age to the middle Rhaetian and document a diverse lowland vegetation adapted to a humid environment. The faunal composition, coprolite assemblage and sedimentary structures point to repeated reworking and concentration of vertebrate remains during short-lived high-energy events. We interpret the Niederschönthal bone bed as having formed in a muddy coastal plain to lagoonal environment with fluvial-estuarine to marine channels having been periodically affected by small-scale transgressive pulses. This study reconciles earlier conflicting interpretations by demonstrating that the bone bed records a complex interplay of terrestrial, freshwater and marine influences rather than a fully marine or purely continental setting.
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