Interbasinal stratigraphic correlation provides the foundation for all consequent continental-sca... more Interbasinal stratigraphic correlation provides the foundation for all consequent continental-scale geological and paleontological analyses. Correlation requires synthesis of lithostratigraphic, biostratigraphic and geochronologic data, and must be periodically updated to accord with advances in dating techniques, changing standards for radiometric dates, new stratigraphic concepts, hypotheses, fossil specimens, and field data. Outdated or incorrect correlation exposes geological and paleontological analyses to potential error. The current work presents a high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. 40 Ar / 39 Ar radiometric dates are newly recalibrated to both current standard and decay constant pairings. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and recalibration corrections in particular affect the relative age positions of the Belly River Group,
ABSTRACT Small-bodied dromaeosaurid and troodontid theropod dinosaurs are present in most of the ... more ABSTRACT Small-bodied dromaeosaurid and troodontid theropod dinosaurs are present in most of the terrestrial Late Cretaceous formations of the North American Western Interior, but are represented predominantly by shed teeth and more rarely by isolated skeletal elements and associated skeletons. The eudromaeosaurian dromaeosaurid Saurornitholestes is among the most commonly recovered small theropods from North America, known from abundant shed teeth, isolated cranial and postcranial elements, and several partial or near-complete skeletons from the Campanian aged Two Medicine Formation of Montana and the Dinosaur Park Formation of Alberta. Conversely, few Saurornitholestes specimens beyond shed teeth have been recovered from temporally equivalent units of the Judith River Formation of Montana. This study reports the first cranial material, a near-complete frontal, referable to Saurornitholestes from the Judith River Formation of Montana. This specimen is the easternmost occurrence of this taxon and was recovered approximately 400 km east of the localities which have produced referred Saurornitholestes specimens in the Two Medicine Formation, proximal to the Cordilleran thrust front. As such, this new specimen indicates that Saurornitholestes was biogeographically widespread and occupied both inland and coastal environments across the northern portions of the Late Cretaceous Western Interior of North America.
Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so fa... more Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is one of several giant titanosaurian sauropods known from the Upper Cretaceous of South America and Asia, but surprisingly not from North America. Here we present the first evidence of giant titanosaurian sauropods from the Upper Cretaceous of North America: two enormous vertebrae and a partial femur, from the Naashoibito Member of the Ojo Alamo Forma− tion, New Mexico, and referred to Alamosaurus sanjuanensis. One of the new vertebrae, a posterior cervical, is compara− ble in size to a posterior cervical described for Puertasaurus: an Argentinosaurus−sized titanosaurian from the Maas− trichtian of Argentina. This makes A. sanjuanensis the largest dinosaur from North America, and among the largest in the world. These findings indicate that A. sanjuanensis is diagnosed based on immature remains, which may have implica− tions for cladistic analyses.
Late Cretaceous deposits of the North American Western Interior represent the best, if not only, ... more Late Cretaceous deposits of the North American Western Interior represent the best, if not only, opportunity to construct a high-resolution chronostratigraphic framework within which to conduct continental-scale geological and paleontological analyses. This is due to the serendipitous combination of large areas of outcrop, interfingering marine units with biostratigraphically informative fossils, and a consistent scattering of radiometric dates due to synorogenic volcanic activity. Accurate correlation is essential for testing a large number of current geological and paleobiological hypotheses; however, despite the large amount of data available, many published correlations suffer from inaccuracies or are simply based on outdated information. Here I present a comprehensive high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. For the first time, nearly two hundred 40 Ar / 39 Ar radiometric dates are recalibrated to both current standard and decay constant pairings, correcting errors in previous recalibrations. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and miscalculations in recently published analyses are corrected which in particular affects the relative age positions of
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian st... more Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian strata (~76.5 Ma) intermediate in age between either of the previously described species of this genus. D. wilsoni displays a unique combination of ancestral and derived characteristics, including a cornual process of the lacrimal reduced in height relative to D. torosus and more basal tyrannosaurines, and a prefrontal with a long axis oriented more rostrally than in D. horneri and more derived tyrannosaurines. The description of this taxon provides insight into evolutionary mode in Tyrannosaurinae, lending strength to previous hypotheses of anagenesis within Daspletosaurus and increasing the resolution with which the evolution of this lineage can be reconstructed. Cladistic phylogenetic methods, stratigraphy, and qualitative analysis of the morphology of relevant taxa supports an anagenetic model for the origin of morphological novelty in this genus, highlighting the predominance of anage...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Late Cretaceous deposits of the North American Western Interior represent the best, if not only, ... more Late Cretaceous deposits of the North American Western Interior represent the best, if not only, opportunity to construct a high-resolution chronostratigraphic framework within which to conduct continental-scale geological and paleontological analyses. This is due to the serendipitous combination of large areas of outcrop, interfingering marine units with biostratigraphically informative fossils, and a consistent scattering of radiometric dates due to synorogenic volcanic activity. Accurate correlation is essential for testing a large number of current geological and paleobiological hypotheses; however, despite the large amount of data available, many published correlations suffer from inaccuracies or are simply based on outdated information. Here I present a comprehensive high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. For the first time, nearly two hu...
(anteroposteriorly thick) vertebrae, well-developed neural spine of the axis, large transverse pr... more (anteroposteriorly thick) vertebrae, well-developed neural spine of the axis, large transverse process of atlas, and median ridge on the dorsal dens. On the contrary, cervical vertebrae in M. yabukii (very short vertebrae, small transverse process of atlas, lack of hyapophyses on the ventral surface, no median ridge on the dorsal dens) appear more derived than the cervical vertebrae in the geologically older edentulous mysticete Eomysticetus (e.g., thick vertebrae, median ridge on the dorsal dens). The disparity in the cervical vertebrae could suggest that Morawanocetus is placed phylogenetically more crown-ward than Eomysticetus and therefore the family Aetiocetidae is not monophyletic. We tested the phylogenetic position of Morawanocetus using the published analysis with addition of postcranial characters. The preliminary result indicated that the family Aetiocetidae is monophyletic, but the robustness of the aetiocetids clade expressed by GC value of standard bootstrap resampling (1000 replicates) was much lowered from the original result. Interestingly, the exclusion of Eomysticetus from the analysis placed Morawanocetus as a sister taxon of the crown mysticetes.
Interbasinal stratigraphic correlation provides the foundation for all consequent continental-sca... more Interbasinal stratigraphic correlation provides the foundation for all consequent continental-scale geological and paleontological analyses. Correlation requires synthesis of lithostratigraphic, biostratigraphic and geochronologic data, and must be periodically updated to accord with advances in dating techniques, changing standards for radiometric dates, new stratigraphic concepts, hypotheses, fossil specimens, and field data. Outdated or incorrect correlation exposes geological and paleontological analyses to potential error. The current work presents a high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. 40 Ar / 39 Ar radiometric dates are newly recalibrated to both current standard and decay constant pairings. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and recalibration corrections in particular affect the relative age positions of the Belly River Group,
ABSTRACT Small-bodied dromaeosaurid and troodontid theropod dinosaurs are present in most of the ... more ABSTRACT Small-bodied dromaeosaurid and troodontid theropod dinosaurs are present in most of the terrestrial Late Cretaceous formations of the North American Western Interior, but are represented predominantly by shed teeth and more rarely by isolated skeletal elements and associated skeletons. The eudromaeosaurian dromaeosaurid Saurornitholestes is among the most commonly recovered small theropods from North America, known from abundant shed teeth, isolated cranial and postcranial elements, and several partial or near-complete skeletons from the Campanian aged Two Medicine Formation of Montana and the Dinosaur Park Formation of Alberta. Conversely, few Saurornitholestes specimens beyond shed teeth have been recovered from temporally equivalent units of the Judith River Formation of Montana. This study reports the first cranial material, a near-complete frontal, referable to Saurornitholestes from the Judith River Formation of Montana. This specimen is the easternmost occurrence of this taxon and was recovered approximately 400 km east of the localities which have produced referred Saurornitholestes specimens in the Two Medicine Formation, proximal to the Cordilleran thrust front. As such, this new specimen indicates that Saurornitholestes was biogeographically widespread and occupied both inland and coastal environments across the northern portions of the Late Cretaceous Western Interior of North America.
Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so fa... more Argentinosaurus (Cenomanian, Argentina) is generally accepted as being the largest dinosaur so far discovered and is one of several giant titanosaurian sauropods known from the Upper Cretaceous of South America and Asia, but surprisingly not from North America. Here we present the first evidence of giant titanosaurian sauropods from the Upper Cretaceous of North America: two enormous vertebrae and a partial femur, from the Naashoibito Member of the Ojo Alamo Forma− tion, New Mexico, and referred to Alamosaurus sanjuanensis. One of the new vertebrae, a posterior cervical, is compara− ble in size to a posterior cervical described for Puertasaurus: an Argentinosaurus−sized titanosaurian from the Maas− trichtian of Argentina. This makes A. sanjuanensis the largest dinosaur from North America, and among the largest in the world. These findings indicate that A. sanjuanensis is diagnosed based on immature remains, which may have implica− tions for cladistic analyses.
Late Cretaceous deposits of the North American Western Interior represent the best, if not only, ... more Late Cretaceous deposits of the North American Western Interior represent the best, if not only, opportunity to construct a high-resolution chronostratigraphic framework within which to conduct continental-scale geological and paleontological analyses. This is due to the serendipitous combination of large areas of outcrop, interfingering marine units with biostratigraphically informative fossils, and a consistent scattering of radiometric dates due to synorogenic volcanic activity. Accurate correlation is essential for testing a large number of current geological and paleobiological hypotheses; however, despite the large amount of data available, many published correlations suffer from inaccuracies or are simply based on outdated information. Here I present a comprehensive high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. For the first time, nearly two hundred 40 Ar / 39 Ar radiometric dates are recalibrated to both current standard and decay constant pairings, correcting errors in previous recalibrations. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and miscalculations in recently published analyses are corrected which in particular affects the relative age positions of
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian st... more Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian strata (~76.5 Ma) intermediate in age between either of the previously described species of this genus. D. wilsoni displays a unique combination of ancestral and derived characteristics, including a cornual process of the lacrimal reduced in height relative to D. torosus and more basal tyrannosaurines, and a prefrontal with a long axis oriented more rostrally than in D. horneri and more derived tyrannosaurines. The description of this taxon provides insight into evolutionary mode in Tyrannosaurinae, lending strength to previous hypotheses of anagenesis within Daspletosaurus and increasing the resolution with which the evolution of this lineage can be reconstructed. Cladistic phylogenetic methods, stratigraphy, and qualitative analysis of the morphology of relevant taxa supports an anagenetic model for the origin of morphological novelty in this genus, highlighting the predominance of anage...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Late Cretaceous deposits of the North American Western Interior represent the best, if not only, ... more Late Cretaceous deposits of the North American Western Interior represent the best, if not only, opportunity to construct a high-resolution chronostratigraphic framework within which to conduct continental-scale geological and paleontological analyses. This is due to the serendipitous combination of large areas of outcrop, interfingering marine units with biostratigraphically informative fossils, and a consistent scattering of radiometric dates due to synorogenic volcanic activity. Accurate correlation is essential for testing a large number of current geological and paleobiological hypotheses; however, despite the large amount of data available, many published correlations suffer from inaccuracies or are simply based on outdated information. Here I present a comprehensive high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. For the first time, nearly two hu...
(anteroposteriorly thick) vertebrae, well-developed neural spine of the axis, large transverse pr... more (anteroposteriorly thick) vertebrae, well-developed neural spine of the axis, large transverse process of atlas, and median ridge on the dorsal dens. On the contrary, cervical vertebrae in M. yabukii (very short vertebrae, small transverse process of atlas, lack of hyapophyses on the ventral surface, no median ridge on the dorsal dens) appear more derived than the cervical vertebrae in the geologically older edentulous mysticete Eomysticetus (e.g., thick vertebrae, median ridge on the dorsal dens). The disparity in the cervical vertebrae could suggest that Morawanocetus is placed phylogenetically more crown-ward than Eomysticetus and therefore the family Aetiocetidae is not monophyletic. We tested the phylogenetic position of Morawanocetus using the published analysis with addition of postcranial characters. The preliminary result indicated that the family Aetiocetidae is monophyletic, but the robustness of the aetiocetids clade expressed by GC value of standard bootstrap resampling (1000 replicates) was much lowered from the original result. Interestingly, the exclusion of Eomysticetus from the analysis placed Morawanocetus as a sister taxon of the crown mysticetes.
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