A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakot... more A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakota was used to study in detail the post-crisis recovery as well as to reconstruct the local environment and its evolution using sedimentology, palynology, fossil floras and vertebrate data. This report will focus on the flora from this site, corresponding to the first appearance data for Paleocene floral recovery, just above the Cretaceous-Tertiary (K/T) Boundary. The studied flora consist of an assemblage of tightly stacked leaves preserved as carbon imprints (also called leaf mats), a preservation condition that makes the extraction of each individual leaf difficult to achieve directly on site. As a result, a new technique was tested, allowing the study of every leaf preserved, their sedimentological context as well as their position relative to each other. A large block of matrix including the leaf mat was jacketed in plaster and was taken to the museum laboratory for analysis under controlled conditions. Preparation consisted of removing sediments at a millimeter scale and recording of placement and orientation of all fossil materials for three-dimensional reconstructions. Using this technique, a description and census of more than 300 leaf specimens was possible within an area of only 0.5 m 2 . The general sedimentological context indicates that the leaves were deposited in a near-stream environment associated with short-term flood events. Detailed information on depositional environment was gathered both by cutting a stratigraphic column from the Hell Creek/Fort Union formational contact up through the basal 4 m of the Fort Union Formation and by studying sediments and leaf preservation mode in detail within the leaf mat. Significant changes in taxonomic abundances correlated with different lithologies was observed, and a leaf species new to the study area was reported. The new methodology proves to be an efficient way to recover additional taphonomic and paleoenvironmental information from leaf mats necessary to understand the depositional dynamics of a fossiliferous leaf site, as well as to improve the record of taxonomic census. In a biostratigraphical prospective, the specimens recovered represent a low-diversity Fort Union flora composed exclusively of dicots that do not exist in the Hell Creek Formation. Preliminary palynological analysis reveal a Cretaceous age for the entire stratigraphic section, implying that the studied leaf mat is part of the FU0 megafloral zone (as defined by the occurrence of a Fort Union flora with Cretaceous palynomorphs). However, this Cretaceous age attribution for the entire section is questioned due to the occurrence of Paranymphaea crassifolia (part of the Paleocene FUI megafloral zone) within another leaf mat located 266 cm above the base of the coal representing the formational contact, and the occurrence of Paleocene PU1 mammals, reported from sediment within the leaf block interval.
The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecos... more The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecosystems, and faunal responses to the one-two punch of severe environmental perturbation and ecosystem collapse are still unclear. Here we report the discovery of in situ terrestrial fossil burrows from just above the impact-defined Cretaceous-Paleogene (K/Pg) boundary in southwestern North Dakota. The crisscrossing networks of horizontal burrows occur at the interface of a lignitic coal and silty sandstone, and reveal intense faunal activity within centimeters of the boundary clay. Estimated rates of sedimentation and coal formation suggest that the burrows were made less than ten thousand years after the end-Cretaceous impact. The burrow characteristics are most consistent with burrows of extant earthworms. Moreover, the burrowing and detritivorous habits of these annelids fit models that predict the trophic and sheltering lifestyles of terrestrial animals that survived the K/Pg extinction event. In turn, such detritus-eaters would have played a critical role in supporting secondary consumers. Thus, some of the carnivorous vertebrates that radiated after the K/Pg extinction may owe their evolutionary success to thriving populations of earthworms.
Much of the debate regarding mass extinction events tend to discuss the relationship between such... more Much of the debate regarding mass extinction events tend to discuss the relationship between such events relative to the moment and timing of internal or external factors (such as volcanism, impact (s), climate, sea-level changes and so on). However, the details of the extinction process itself is still poorly understood, and most of the analysis are based on biodiversity patterns without integrating the biogeographic and environmental context. Another way of approaching the problem would be to propose precise ...
Review of Palaeobotany and Palynology, Sep 30, 2008
A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakot... more A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakota was used to study in detail the post-crisis recovery as well as to reconstruct the local environment and its evolution using sedimentology, palynology, fossil floras and vertebrate data. This report will focus on the flora from this site, corresponding to the first appearance data for Paleocene floral recovery, just above the Cretaceous–Tertiary (K/T) Boundary. The studied flora consist of an assemblage of tightly stacked leaves preserved as carbon ...
The Cretaceous/Tertiary (K/T) boundary corresponds to one of the very few unique events in the ge... more The Cretaceous/Tertiary (K/T) boundary corresponds to one of the very few unique events in the geological record discovered to date, representing a single traceable timeline across the world. This timeline, coincident with the geochemical and mineralogical singularities caused by the impact of a large extraterrestrial body, is also coincident with the end-Cretaceous extinction event in North America. This precise timeline gives an ideal context for comparing the trends recorded by the different groups of the terrestrial fossil record during the K/T ...
A nearly complete turtle shell from the Late Cretaceous (Maastrichtian) Hell Creek Formation of S... more A nearly complete turtle shell from the Late Cretaceous (Maastrichtian) Hell Creek Formation of Slope County, North Dakota, represents the most complete remains to date of a Mesozoic kinosternoid turtle and a new species, Hoplochelys clark nov. sp. The new taxon is diagnosable from other representatives of Hoplochelys by the plesiomorphic placement of the humeral/femoral sulcus behind the hyo/hypoplastral suture and the autapomorphic development of an interrupted median (neural) keel. All six previously named Paleocene (Puercan and Torrejonian) representatives of Hoplochelys lack diagnostic characters and are synonymized as Hoplochelys crassa. A phylogenetic analysis reveals that Hoplochelys spp. and Agomphus pectoralis are most parsimoniously placed within Kinosternoidea along the phylogenetic stem of the extant Mesoamerican River Turtle Dermatemys mawii, extending that taxon's stem lineage from the early Eocene to the late Maastrichtian. The two primary crown lineages of Kinosternoidea are thus known from the Mesozoic and split prior to the late Campanian. The presence of a thickened cruciform plastron, true costiform processes, only three inframarginals, and the reduction of the medial contact of the abdominals are synapomorphies of Chelydroidea, the clade formed by Chelydridae and Kinosternoidae.
This study documents the terrestrial palynological record at the John's Nose section, a new ... more This study documents the terrestrial palynological record at the John's Nose section, a new Cretaceous–Paleogene (K–Pg) boundary site in North Dakota, USA. In addition to Mud Buttes and Pyramid Butte, John's Nose represents the third K–Pg section in southwestern North Dakota that preserves direct evidence of the Chicxulub asteroid impact, allowing for direct comparison over the timing and trends of the palynological record in respect to this event. The palynological analysis of John's Nose section reveals the presence of 68 ...
A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakot... more A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakota was used to study in detail the post-crisis recovery as well as to reconstruct the local environment and its evolution using sedimentology, palynology, fossil floras and vertebrate data. This report will focus on the flora from this site, corresponding to the first appearance data for Paleocene floral recovery, just above the Cretaceous-Tertiary (K/T) Boundary. The studied flora consist of an assemblage of tightly stacked leaves preserved as carbon imprints (also called leaf mats), a preservation condition that makes the extraction of each individual leaf difficult to achieve directly on site. As a result, a new technique was tested, allowing the study of every leaf preserved, their sedimentological context as well as their position relative to each other. A large block of matrix including the leaf mat was jacketed in plaster and was taken to the museum laboratory for analysis under controlled conditions. Preparation consisted of removing sediments at a millimeter scale and recording of placement and orientation of all fossil materials for three-dimensional reconstructions. Using this technique, a description and census of more than 300 leaf specimens was possible within an area of only 0.5 m 2 . The general sedimentological context indicates that the leaves were deposited in a near-stream environment associated with short-term flood events. Detailed information on depositional environment was gathered both by cutting a stratigraphic column from the Hell Creek/Fort Union formational contact up through the basal 4 m of the Fort Union Formation and by studying sediments and leaf preservation mode in detail within the leaf mat. Significant changes in taxonomic abundances correlated with different lithologies was observed, and a leaf species new to the study area was reported. The new methodology proves to be an efficient way to recover additional taphonomic and paleoenvironmental information from leaf mats necessary to understand the depositional dynamics of a fossiliferous leaf site, as well as to improve the record of taxonomic census. In a biostratigraphical prospective, the specimens recovered represent a low-diversity Fort Union flora composed exclusively of dicots that do not exist in the Hell Creek Formation. Preliminary palynological analysis reveal a Cretaceous age for the entire stratigraphic section, implying that the studied leaf mat is part of the FU0 megafloral zone (as defined by the occurrence of a Fort Union flora with Cretaceous palynomorphs). However, this Cretaceous age attribution for the entire section is questioned due to the occurrence of Paranymphaea crassifolia (part of the Paleocene FUI megafloral zone) within another leaf mat located 266 cm above the base of the coal representing the formational contact, and the occurrence of Paleocene PU1 mammals, reported from sediment within the leaf block interval.
The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecos... more The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecosystems, and faunal responses to the one-two punch of severe environmental perturbation and ecosystem collapse are still unclear. Here we report the discovery of in situ terrestrial fossil burrows from just above the impact-defined Cretaceous-Paleogene (K/Pg) boundary in southwestern North Dakota. The crisscrossing networks of horizontal burrows occur at the interface of a lignitic coal and silty sandstone, and reveal intense faunal activity within centimeters of the boundary clay. Estimated rates of sedimentation and coal formation suggest that the burrows were made less than ten thousand years after the end-Cretaceous impact. The burrow characteristics are most consistent with burrows of extant earthworms. Moreover, the burrowing and detritivorous habits of these annelids fit models that predict the trophic and sheltering lifestyles of terrestrial animals that survived the K/Pg extinction event. In turn, such detritus-eaters would have played a critical role in supporting secondary consumers. Thus, some of the carnivorous vertebrates that radiated after the K/Pg extinction may owe their evolutionary success to thriving populations of earthworms.
Much of the debate regarding mass extinction events tend to discuss the relationship between such... more Much of the debate regarding mass extinction events tend to discuss the relationship between such events relative to the moment and timing of internal or external factors (such as volcanism, impact (s), climate, sea-level changes and so on). However, the details of the extinction process itself is still poorly understood, and most of the analysis are based on biodiversity patterns without integrating the biogeographic and environmental context. Another way of approaching the problem would be to propose precise ...
Review of Palaeobotany and Palynology, Sep 30, 2008
A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakot... more A stratigraphic section in the basal Fort Union Formation (Paleocene) in southwestern North Dakota was used to study in detail the post-crisis recovery as well as to reconstruct the local environment and its evolution using sedimentology, palynology, fossil floras and vertebrate data. This report will focus on the flora from this site, corresponding to the first appearance data for Paleocene floral recovery, just above the Cretaceous–Tertiary (K/T) Boundary. The studied flora consist of an assemblage of tightly stacked leaves preserved as carbon ...
The Cretaceous/Tertiary (K/T) boundary corresponds to one of the very few unique events in the ge... more The Cretaceous/Tertiary (K/T) boundary corresponds to one of the very few unique events in the geological record discovered to date, representing a single traceable timeline across the world. This timeline, coincident with the geochemical and mineralogical singularities caused by the impact of a large extraterrestrial body, is also coincident with the end-Cretaceous extinction event in North America. This precise timeline gives an ideal context for comparing the trends recorded by the different groups of the terrestrial fossil record during the K/T ...
A nearly complete turtle shell from the Late Cretaceous (Maastrichtian) Hell Creek Formation of S... more A nearly complete turtle shell from the Late Cretaceous (Maastrichtian) Hell Creek Formation of Slope County, North Dakota, represents the most complete remains to date of a Mesozoic kinosternoid turtle and a new species, Hoplochelys clark nov. sp. The new taxon is diagnosable from other representatives of Hoplochelys by the plesiomorphic placement of the humeral/femoral sulcus behind the hyo/hypoplastral suture and the autapomorphic development of an interrupted median (neural) keel. All six previously named Paleocene (Puercan and Torrejonian) representatives of Hoplochelys lack diagnostic characters and are synonymized as Hoplochelys crassa. A phylogenetic analysis reveals that Hoplochelys spp. and Agomphus pectoralis are most parsimoniously placed within Kinosternoidea along the phylogenetic stem of the extant Mesoamerican River Turtle Dermatemys mawii, extending that taxon's stem lineage from the early Eocene to the late Maastrichtian. The two primary crown lineages of Kinosternoidea are thus known from the Mesozoic and split prior to the late Campanian. The presence of a thickened cruciform plastron, true costiform processes, only three inframarginals, and the reduction of the medial contact of the abdominals are synapomorphies of Chelydroidea, the clade formed by Chelydridae and Kinosternoidae.
This study documents the terrestrial palynological record at the John's Nose section, a new ... more This study documents the terrestrial palynological record at the John's Nose section, a new Cretaceous–Paleogene (K–Pg) boundary site in North Dakota, USA. In addition to Mud Buttes and Pyramid Butte, John's Nose represents the third K–Pg section in southwestern North Dakota that preserves direct evidence of the Chicxulub asteroid impact, allowing for direct comparison over the timing and trends of the palynological record in respect to this event. The palynological analysis of John's Nose section reveals the presence of 68 ...
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