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ABSTRACT Natural river diversion, or avulsion, controls the distribution of channels on a floodplain and channel sandstone bodies within fluvial stratigraphic architecture. Avulsions establish new flow paths and create channels through several recognized processes, or styles. These include reoccupying existing channels, or annexation, downcutting into the floodplain, or incision, and constructing new channels from crevasse‐splay distributary networks, or progradation. Recent remote sensing observations show that avulsion style changes systematically moving downstream along modern fluvial fans but, to date, no studies have assessed the significance of these trends on fluvial fan stratigraphy. Here, spatiotemporal changes in avulsion stratigraphy are investigated within the Salt Wash Member of the Morrison Formation, deposited in the Cordilleran foreland basin during the Late Jurassic epoch. Measured sections and photographic panels were analysed from 23 locations across the Salt Wash extent. Avulsion style was identified in the stratigraphic record by the basal contact of a channel storey with underlying strata: channel–channel contacts indicate annexation, channel–floodplain contacts indicate incision and channel–heterolithic contacts indicate progradation. Contact types change downstream, such that channel–channel and channel–floodplain contacts dominate proximal locations, while channel–heterolithic contacts become increasingly prevalent downstream. Outcrop results were compared to a numerical model of fluvial fan formation and remote‐sensing analysis of avulsions on modern fans. In both additional datasets, channels in proximal fan positions tend to avulse via annexation, reoccupying abandoned channels, while channels in more distal positions tend to avulse via increasingly significant progradation. These findings suggest a relationship between newly recognized downstream changes in avulsion style and well‐established downstream changes in fluvial fan architecture. Furthermore, this suggests that fan architecture can inform interpretations of ancient fluvial dynamics, including avulsion behaviour, and that avulsions can cause stratigraphically significant and measurable changes to fan architecture. [ABSTRACT FROM AUTHOR]

The Upper Jurassic Morrison Formation sauropods Diplodocus (formerly “Seismosaurus”) hallorum and Supersaurus vivianae are quantifiably the largest dinosaurian taxa from the formation, as well as being among the largest dinosaurs in the world. Their extreme body size (in particular body length, c. 50+ m) has fascinated the paleontological community since their discoveries and has sparked an ongoing discussion on the trends and limits of Morrison Formation sauropod body size. Although not an undeviating proxy, often the largest and skeletally most mature specimens are among the rarest (as exemplified in Triceratops). While their body size has no phylogenetic bearing, the extreme size and potential eco and biological significance of these two sauropod taxa are frequently discussed. Whether these rare and titanically proportioned sauropod specimens are large‐bodied, senescent or both is an often‐repeating rhetoric. To definitively make maturational inferences about these taxa, we osteohistologically sampled the holotype of D. hallorum (NMMNH P‐25079) and the second known specimen of S. vivianae (WDC DMJ‐021). Our age‐determinant and maturational assessments indicate that both specimens were skeletally mature at their respective age of death. Retrocalculation methods for D. hallorum NMMNH P‐25079 produce a maximum age‐at‐death estimation of 60 years, whereas S. vivianae WDC DMJ‐021 lived well past skeletal maturity—so much so that reliable retrocalculated ages cannot be accurately determined at this time. Additionally, the rarity of such large sauropods within the Morrison Formation might be more parsimoniously explained as relating to their maturity as opposed to representing aberrant taxa on the Morrison landscape. [ABSTRACT FROM AUTHOR]

To reconstruct a fossil forest in three dimensions, an accurate estimation of tree height is crucial. However, modelling the height-diameter relationship of ancient trees is difficult, because the trunks of fossil trees are usually fragmentary, making direct height measurements impossible. One practical approach for reconstructing ancient tree height is to use growth models based on the height-diameter relationships of the nearest living relatives of fossil taxa. Here we apply 19 models to describe height-diameter relationships of living Araucaria trees for establishing appropriate models for ancient Araucariaceae trees. Data come from four living populations of Araucaria: A. bidwillii and A. cunninghamii in Queensland, Australia, and A. cunninghamii and A. hunsteinii in New Guinea. According to an AIC-based model selection, a power function with an exponent of 0.67 (termed here the modified Mosbrugger model) is found to be the most appropriate for each population and for the entire dataset (157 trees), but normalization constants differ across populations. To find the most appropriate models for the genus Araucaria, 100 random samples (each population generating 25 random samples) from the entire dataset are used. Based on 100 curve fitting results on each model and multiple performance criteria, three median models are generated from the medians of their parameter estimates. Of these, the median 2pPower model works best for Araucaria, but the modified Mosbrugger and Curtis models perform nearly as well. In a case study, we revise tree heights of Upper Jurassic araucariaceous logs in Utah, USA, by applying these three models. [ABSTRACT FROM AUTHOR]

The Wanakah Formation and Tidwell Member of the Morrison Formation record intervals of paedogenesis in the Paradox Basin and Central Colorado trough, western Colorado during the Middle-Late Jurassic. Detailed field description of paleosols and paedogenic carbonates at different stratigraphic horizons from three localities document four main pedotypes: vertisols, gleysols, oxisols, and protosols. Generally, gleysols reflect reducing conditions, protosols and oxisols reflect oxidizing conditions, and vertisols reflect fluctuations in oxidizing/reducing conditions (seasonality). Major elemental geochemical ratios in samples from these paleosols suggest variable redox conditions and a sub-humid to humid paleoclimate with seasonal precipitations during paleosol development. Estimated mean annual temperature based on elemental analyses of paleosol B in paleosols from Ribbon Trail and Escalante Canyon in western Colorado suggest mesic – thermic paleoclimate. Mean annual precipitation indicates sub-humid to humid regional palaeoclimatic conditions marked by seasonal precipitation. Clay mineralogy of these paleosols, determined by X-ray diffraction, shows the abundance of illite most likely formed from smectite alteration due to episodic wetting and drying. δ13C and δ18O isotope analyses of carbonate veins in these paleosols suggest that they formed recently from meteoric water and therefore are not considered for palaeoclimatic reconstructions. Mean annual temperature and mean annual precipitation estimates in the Wanakah Formation and Tidwell Member of the Morrison Formation provide new information on the local and regional palaeoclimatic and paleoenvironmental conditions during the Middle Jurassic in western Colorado as well as data for comparison with the Upper Morrison paleoclimate from northern and southern localities in the western United States. [ABSTRACT FROM AUTHOR]

Here, we describe a pathological sub-adult theropod dinosaur from the Late Jurassic Morrison Formation in Dana Quarry, Wyoming, U.S.A. It exhibits multiple pathologies, involving three dorsal vertebrae, the right scapula and coracoid, and apparent pathology of the left scapula. The fourth dorsal vertebra has four irregularly shaped growths on the vertebral arch. The eighth and ninth vertebrae are fused. The scapulocoracoid joint has an obvious deformity. The distal part of the right scapula is more rounded than normal. The left scapula has a depression on the lateral blade. These pathologies can be identified as follows: the fourth dorsal vertebra is possibly neoplastic or exhibiting compensatory hyperplasia; the eighth and ninth vertebral and the right scapular pathology are consistent with spondyloarthropathy. Diagnoses considered for the left scapula pathology are infections, trauma or unknown. The animal survived the pathologies, which are unlikely the cause of its death. This specimen represents the first known occurrence of spondyloarthropathy in a theropod. [ABSTRACT FROM AUTHOR]

We reexamine and redescribe the type specimens and other associated material of the Late Jurassic rhynchocephalian Opisthias rarus, from Quarry 9 of the Morrison Formation. We rediscover and describe a fragment of rock matrix belonging to the holotype that is presented for the first time, and we also comment on undescribed material from Quarry 9 that possibly belongs to an unnamed species of Opisthias. In addition, we describe a new specimen of Theretairus antiquus that helps to reject its proposed status as a junior synonym of O. rarus, and contributes to increase the knowledge of the microvertebrate fauna of the Late Jurassic of North America.

We describe a new, small-bodied rhynchocephalian reptile, Opisthiamimus gregori gen. et sp. nov., from the Upper Jurassic Morrison Formation of Wyoming, USA. Whereas many fossil rhynchocephalians are based on isolated incomplete jaws, the holotype of O. gregori includes most of the skull and postcranium and therefore represents one of the most complete specimens of Rhynchocephalia known from North America. We used micro-computed tomography to examine its skeletal anatomy in detail and to develop a three-dimensional reconstruction of the skull. The skull of O. gregori is similar to that of several non-neosphenodontian rhynchocephalians such as Planocephalosaurus (e.g. large orbits) and Clevosaurus (e.g. parietal parasagittal crests) yet exhibits a suite of other features related to the proal shearing mechanism that becomes increasingly elaborated among more phylogenetically nested taxa such as Sphenodon (e.g. lateral palatine tooth row parallels maxillary tooth row along its entire length, pyramidal dentary teeth with mesial shearing crests). The postcranial skeleton of O. gregori exhibits characteristics typical of a terrestrial rhynchocephalian. Our phylogenetic analyses use a substantially updated data set of 118 characters and 46 taxa, and both maximum parsimony and Bayesian frameworks. Results place O. gregori inside Eusphenodontia but outside Neosphenodontia, and therefore in a key position for contributing to character polarity for more deeply nested clades such as Clevosauridae, Sphenodontidae and Pleurosauridae. We also erect Leptorhynchia taxon nov., composed primarily of aquatically adapted taxa (e.g. Pleurosaurus, Sapheosaurus), which is supported by both cranial and postcranial characters. Because O. gregori is not particularly closely related to the other named Morrison rhynchocephalians (e.g. Opisthias rarus), it increases both the alpha and beta taxonomic diversities within the formation. Similarly, major differences in body size and inferred diet of the Morrison taxa imply considerable concomitant palaeoecological diversity just prior to a major global decline in rhynchocephalian diversity around the close of the Jurassic. [ABSTRACT FROM AUTHOR]

We describe two skull fragments of a new morganucodontan from the Cisco Mammal Quarry (Upper Jurassic Morrison Formation), preserving portions of the palate and snout in excellent 3D detail as well as the complete upper postcanine dentition. Morganucodontans are best known by isolated elements and relatively complete skulls of several species of Morganucodon from the Lower Jurassic of Wales and China; this group is fundamental to our understanding of the early evolution of mammals. Cifellilestes ciscoensis gen. et sp. nov. possesses derived features of the snout paired with plesiomorphic construction of the molars; the distal premolars are complex and there is an unusually low count (two) of strongly imbricated molars. This character combination expands craniodental variation for the group. We sampled mudstone from the Cisco Mammal Quarry for ash-fall zircon analysis and obtained a date of 151.50 ± 0.28 Ma. This dates the locality to the earliest Tithonian and slightly younger than other major dated mammal-bearing localities in the Morrison Formation. Cifellilestes represents one of the youngest members of this group and extends the record of morganucodontans in North America by more than 30 Ma. Morganucodontans are a rare component of Late Jurassic faunas but display surprising dental diversity through variations in a tooth count and cusp morphology of a deeply conserved, generalized mammalian tooth pattern, which was fully established in brasilodontid (non-mammalian) ancestors at least 80 my prior.

We reexamine and redescribe the type specimens and other associated material of the Late Jurassic rhynchocephalian Opisthias rarus, from Quarry 9 of the Morrison Formation. We rediscover and describe a fragment of rock matrix belonging to the holotype that is presented for the first time, and we also comment on undescribed material from Quarry 9 that possibly belongs to an unnamed species of Opisthias. In addition, we describe a new specimen of Theretairus antiquus that helps to reject its proposed status as a junior synonym of O. rarus, and contributes to increase the knowledge of the microvertebrate fauna of the Late Jurassic of North America. [ABSTRACT FROM AUTHOR]

A new specimen of Haplocanthosaurus is described based on bones excavated from the Late Jurassic Dry Mesa Dinosaur Quarry near Delta, Colorado. The specimen consists of seven dorsal vertebrae and a right tibia and is identified as Haplocanthosaurus based on the dorsally angled transverse processes, tall neural arch peduncles, low parapophyses relative to the diapophyses in the posterior dorsal vertebrae, and the robustness of the tibia combined with a greatly expanded distal articular surface. The discovery adds to our understanding of the biostratigraphy of Haplocanthosaurus, showing this genus is definitively present in the Brushy Basin Member of the Morrison Formation, and making this individual the geologically youngest Haplocanthosaurus specimen on the Colorado Plateau. The identification of this genus adds to the known diversity of sauropods at Dry Mesa Dinosaur Quarry (DMDQ), which is at least six distinct genera, making DMDQ the most diverse single locality of sauropods in the Morrison Formation and the world., (© 2024 The Author(s). The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

We describe two skull fragments of a new morganucodontan from the Cisco Mammal Quarry (Upper Jurassic Morrison Formation), preserving portions of the palate and snout in excellent 3D detail as well as the complete upper postcanine dentition. Morganucodontans are best known by isolated elements and relatively complete skulls of several species of Morganucodon from the Lower Jurassic of Wales and China; this group is fundamental to our understanding of the early evolution of mammals. Cifellilestes ciscoensis gen. et sp. nov. possesses derived features of the snout paired with plesiomorphic construction of the molars; the distal premolars are complex and there is an unusually low count (two) of strongly imbricated molars. This character combination expands craniodental variation for the group. We sampled mudstone from the Cisco Mammal Quarry for ash-fall zircon analysis and obtained a date of 151.50 ± 0.28 Ma. This dates the locality to the earliest Tithonian and slightly younger than other major dated mammal-bearing localities in the Morrison Formation. Cifellilestes represents one of the youngest members of this group and extends the record of morganucodontans in North America by more than 30 Ma. Morganucodontans are a rare component of Late Jurassic faunas but display surprising dental diversity through variations in a tooth count and cusp morphology of a deeply conserved, generalized mammalian tooth pattern, which was fully established in brasilodontid (non-mammalian) ancestors at least 80 my prior. [ABSTRACT FROM AUTHOR]

The first fossil hemipteran from the Late Jurassic of North America, Morrisonnepa jurassica n. gen. et n. sp., is reported and described from the Morrison Formation, Jurassic Salad Bar locality, San Juan County, Utah, USA. The new specimen is characterised and illustrated, showing morphological characters similar to nepomorphs such as forewing well-developed and folded flat on the abdomen, oval abdomen shape, and the presence of a short pair of appendages. The taxonomic allocation close to members of the Nepomorpha is discussed. Morrisonnepa jurassica n. gen. et n. sp. was collected with abundant plants, spinicaudatan carapaces, and a small amphibian from a finely laminated shale that overlies a coarser plant debris bed, supporting the presence of a possible oxbow lake or pond, environments developed within the greater ecosystem of the Morrison Formation during the Late Jurassic. In this context, we analyse the taphonomic and palaeoecological implications of the presence of aquatic insects. Besides providing morphological information on Jurassic nepomorphs, the new fossil helps illustrate how the aquatic insect assemblage was integrated during the Jurassic in North America. [ABSTRACT FROM AUTHOR]

Sauropod dinosaurs were an abundant and diverse component of the Upper Jurassic Morrison Formation of the USA, with 24 currently recognized species. However, some authors consider this high diversity to have been ecologically unviable and the validity of some species has been questioned, with suggestions that they represent growth series (ontogimorphs) of other species. Under this scenario, high sauropod diversity in the Late Jurassic of North America is greatly overestimated. One putative ontogimorph is the enigmatic diplodocoid Amphicoelias altus, which has been suggested to be synonymous with Diplodocus. Given that Amphicoelias was named first, it has priority and thus Diplodocus would become its junior synonym. Here, we provide a detailed re-description of A. altus in which we restrict it to the holotype individual and support its validity, based on three autapomorphies. Constraint analyses demonstrate that its phylogenetic position within Diplodocoidea is labile, but it seems unlikely that Amphicoelias is synonymous with Diplodocus. As such, our re-evaluation also leads us to retain Diplodocus as a distinct genus. There is no evidence to support the view that any of the currently recognized Morrison sauropod species are ontogimorphs. Available data indicate that sauropod anatomy did not dramatically alter once individuals approached maturity. Furthermore, subadult sauropod individuals are not prone to stemward slippage in phylogenetic analyses, casting doubt on the possibility that their taxonomic affinities are substantially misinterpreted. An anatomical feature can have both an ontogenetic and phylogenetic signature, but the former does not outweigh the latter when other characters overwhelmingly support the affinities of a taxon. Many Morrison Formation sauropods were spatio-temporally and/or ecologically separated from one another. Combined with the biases that cloud our reading of the fossil record, we contend that the number of sauropod dinosaur species in the Morrison Formation is currently likely to be underestimated, not overestimated.

Two partial skeletons from Montana represent the northernmost occurrences of Stegosauria within North America. One of these specimens represents the northernmost dinosaur fossil ever recovered from the Morrison Formation. Consisting of fragmentary cranial and postcranial remains, these specimens are contributing to our knowledge of the record and distribution of dinosaurs within the Morrison Formation from Montana. While the stegosaurs of the Morrison Formation consist of Alcovasaurus, Hesperosaurus, and Stegosaurus, the only positively identified stegosaur from Montana thus far is Hesperosaurus. Unfortunately, neither of these new specimens exhibit diagnostic autapomorphies. Nonetheless, these specimens are important data points due to their geographic significance, and some aspects of their morphologies are striking. In one specimen, the teeth express a high degree of wear usually unobserved within this clade—potentially illuminating the progression of the chewing motion in derived stegosaurs. Other morphologies, though not histologically examined in this analysis, have the potential to be important indicators for maturational inferences. In suite with other specimens from the northern extent of the formation, these specimens contribute to the ongoing discussion that body size may be latitudinally significant for stegosaurs—an intriguing geographical hypothesis which further emphasizes that size is not an undeviating proxy for maturity in dinosaurs.

The Late Jurassic Allosaurus is one of the better-studied dinosaurs. A histological and geochemical study of a tibia and a femur of A. fragilis recovered in the Upper Jurassic Cleveland-Lloyd Dinosaur Quarry, Utah, United States has been done in order to address growth characteristics of this species. The two bones, probably belonging to separate individuals, are among the largest known for this species, which make them suitable to address such issues. The inclusion of our data on femur growth markings in the previously published data reflects a range of growth variability rather than two distinct growth strategies. The tibia has a well-developed external fundamental system indicating somatic maturity achievement. Using a quantitative method of superimposition to retrocalculate missing lines of arrested growth, the tibia appears to correspond to an individual that reached its skeletal maturity at 22 years and died at approximately 26 years. In the tibia, the concentration of zinc, a potential biomarker associated with bone formation, displays a higher concentration in zones of rapid growth compared to annuli. There is no direct relationship between the values of δ18Op and the lines of arrested growth distribution. The absence of relations between the histological organization and an enrichment in REE of the bone, indicates that the variations of δ18Op likely represent a diagenetic process rather than a primordial, biologic composition. However, the geochemical composition of the bones is not homogeneous along the sections, indicating that the signal variations have not been completely erased by diagenesis.

Allosaurus, from the Late Jurassic of North America and Europe, is a model taxon for Jurassic basal tetanuran theropod dinosaurs. It has achieved an almost iconic status due to its early discovery in the late, 19th century, and due to the abundance of material from the Morrison Formation of the western U.S.A., making Allosaurus one of the best-known theropod taxa. Despite this, various aspects of the cranial anatomy of Allosaurus are surprisingly poorly understood. Here, we discuss the osteology of the cheek region, comprised by the jugal, maxilla, and lacrimal. This region of the skull is of importance for Allosaurus taxonomy and phylogeny, particularly because Allosaurus has traditionally been reconstructed with an unusual cheek configuration, and because the European species Allosaurus europaeus has been said to be different from North American material in the configuration of these bones. Based on re-examination of articulated and disarticulated material from a number of repositories, we show that the jugal participates in the antorbital fenestra, contradicting the common interpretation. The jugal laterally overlies the lacrimal, and forms an extended antorbital fossa with this bone. Furthermore, we document previously unrecorded pneumatic features of the jugal of Allosaurus.

Allosaurus is one of the best known theropod dinosaurs from the Jurassic and a crucial taxon in phylogenetic analyses. On the basis of an in-depth, firsthand study of the bulk of Allosaurus specimens housed in North American institutions, we describe here a new theropod dinosaur from the Upper Jurassic Morrison Formation of Western North America, Allosaurus jimmadseni sp. nov., based upon a remarkably complete articulated skeleton and skull and a second specimen with an articulated skull and associated skeleton. The present study also assigns several other specimens to this new species, Allosaurus jimmadseni, which is characterized by a number of autapomorphies present on the dermal skull roof and additional characters present in the postcrania. In particular, whereas the ventral margin of the jugal of Allosaurus fragilis has pronounced sigmoidal convexity, the ventral margin is virtually straight in Allosaurus jimmadseni. The paired nasals of Allosaurus jimmadseni possess bilateral, blade-like crests along the lateral margin, forming a pronounced nasolacrimal crest that is absent in Allosaurus fragilis.

Allosaurus, from the Late Jurassic of North America and Europe, is a model taxon for Jurassic basal tetanuran theropod dinosaurs. It has achieved an almost iconic status due to its early discovery in the late, 19th century, and due to the abundance of material from the Morrison Formation of the western U.S.A., making Allosaurus one of the best-known theropod taxa. Despite this, various aspects of the cranial anatomy of Allosaurus are surprisingly poorly understood. Here, we discuss the osteology of the cheek region, comprised by the jugal, maxilla, and lacrimal. This region of the skull is of importance for Allosaurus taxonomy and phylogeny, particularly because Allosaurus has traditionally been reconstructed with an unusual cheek configuration, and because the European species Allosaurus europaeus has been said to be different from North American material in the configuration of these bones. Based on re-examination of articulated and disarticulated material from a number of repositories, we show that the jugal participates in the antorbital fenestra, contradicting the common interpretation. The jugal laterally overlies the lacrimal, and forms an extended antorbital fossa with this bone. Furthermore, we document previously unrecorded pneumatic features of the jugal of Allosaurus. [ABSTRACT FROM AUTHOR]

Allosaurus is one of the best known theropod dinosaurs from the Jurassic and a crucial taxon in phylogenetic analyses. On the basis of an in-depth, firsthand study of the bulk of Allosaurus specimens housed in North American institutions, we describe here a new theropod dinosaur from the Upper Jurassic Morrison Formation of Western North America, Allosaurus jimmadseni sp. nov., based upon a remarkably complete articulated skeleton and skull and a second specimen with an articulated skull and associated skeleton. The present study also assigns several other specimens to this new species, Allosaurus jimmadseni, which is characterized by a number of autapomorphies present on the dermal skull roof and additional characters present in the postcrania. In particular, whereas the ventral margin of the jugal of Allosaurus fragilis has pronounced sigmoidal convexity, the ventral margin is virtually straight in Allosaurus jimmadseni. The paired nasals of Allosaurus jimmadseni possess bilateral, blade-like crests along the lateral margin, forming a pronounced nasolacrimal crest that is absent in Allosaurus fragilis. [ABSTRACT FROM AUTHOR]

The last two decades have seen a remarkable increase in the known diversity of basal avialans and their paravian relatives. The lack of resolution in the relationships of these groups combined with attributing the behavior of specialized taxa to the base of Paraves has clouded interpretations of the origin of avialan flight. Here, we describe Hesperornithoides miessleri gen. et sp. nov., a new paravian theropod from the Morrison Formation (Late Jurassic) of Wyoming, USA, represented by a single adult or subadult specimen comprising a partial, well-preserved skull and postcranial skeleton. Limb proportions firmly establish Hesperornithoides as occupying a terrestrial, non-volant lifestyle. Our phylogenetic analysis emphasizes extensive taxonomic sampling and robust character construction, recovering the new taxon most parsimoniously as a troodontid close to Daliansaurus, Xixiasaurus, and Sinusonasus. Multiple alternative paravian topologies have similar degrees of support, but proposals of basal paravian archaeopterygids, avialan microraptorians, and Rahonavis being closer to Pygostylia than archaeopterygids or unenlagiines are strongly rejected. All parsimonious results support the hypothesis that each early paravian clade was plesiomorphically flightless, raising the possibility that avian flight originated as late as the Late Jurassic or Early Cretaceous.

Two partial skeletons from Montana represent the northernmost occurrences of Stegosauria within North America. One of these specimens represents the northernmost dinosaur fossil ever recovered from the Morrison Formation. Consisting of fragmentary cranial and postcranial remains, these specimens are contributing to our knowledge of the record and distribution of dinosaurs within the Morrison Formation from Montana. While the stegosaurs of the Morrison Formation consist of Alcovasaurus, Hesperosaurus, and Stegosaurus, the only positively identified stegosaur from Montana thus far is Hesperosaurus. Unfortunately, neither of these new specimens exhibit diagnostic autapomorphies. Nonetheless, these specimens are important data points due to their geographic significance, and some aspects of their morphologies are striking. In one specimen, the teeth express a high degree of wear usually unobserved within this clade--potentially illuminating the progression of the chewing motion in derived stegosaurs. Other morphologies, though not histologically examined in this analysis, have the potential to be important indicators for maturational inferences. In suite with other specimens from the northern extent of the formation, these specimens contribute to the ongoing discussion that body size may be latitudinally significant for stegosaurs--an intriguing geographical hypothesis which further emphasizes that size is not an undeviating proxy for maturity in dinosaurs. [ABSTRACT FROM AUTHOR]

The last two decades have seen a remarkable increase in the known diversity of basal avialans and their paravian relatives. The lack of resolution in the relationships of these groups combined with attributing the behavior of specialized taxa to the base of Paraves has clouded interpretations of the origin of avialan flight. Here, we describe Hesperornithoides miessleri gen. et sp. nov., a new paravian theropod from the Morrison Formation (Late Jurassic) of Wyoming, USA, represented by a single adult or subadult specimen comprising a partial, well-preserved skull and postcranial skeleton. Limb proportions firmly establish Hesperornithoides as occupying a terrestrial, non-volant lifestyle. Our phylogenetic analysis emphasizes extensive taxonomic sampling and robust character construction, recovering the new taxon most parsimoniously as a troodontid close to Daliansaurus, Xixiasaurus, and Sinusonasus. Multiple alternative paravian topologies have similar degrees of support, but proposals of basal paravian archaeopterygids, avialan microraptorians, and Rahonavis being closer to Pygostylia than archaeopterygids or unenlagiines are strongly rejected. All parsimonious results support the hypothesis that each early paravian clade was plesiomorphically flightless, raising the possibility that avian flight originated as late as the Late Jurassic or Early Cretaceous. [ABSTRACT FROM AUTHOR]

Jurassic paleomagnetic data from North America have long been contentious, generating ambiguities in the shape of the global‐composite apparent polar wander path. Here we show from a restudy of two subdivisions of the Late Jurassic Morrison Formation at the classic locality at Norwood on the Colorado Plateau that the derived paleopoles reflect variable overprinting probably in the Cretaceous and are of limited value for apparent polar wander determination. We instead assembled an updated set of Jurassic paleopoles from parauthocthonous Adria, the African promontory, using primary paleomagnetic component directions derived from stratigraphically superposed intervals and corrected for sedimentary inclination error. These paleopoles are found to be in superb agreement with independent igneous paleopoles from the literature across the so‐called Jurassic monster polar shift, which in North American coordinates is a jump of ~30° arc distance from the 190‐ to 160‐Ma stillstand pole at 79.5°N 104.8°E to a 148 ± 3.5‐Ma pole at 60.8°N 200.6°E defined by four Adria sedimentary paleopoles and the published Ithaca, Hinlopenstretet, and Swartsruggens‐Bumbeni igneous paleopoles. The implied high rate of polar motion of ~2.5°/Myr across the monster shift is compatible with maximum theoretical estimates for true polar wander. We include a critique of published Jurassic paleomagnetic data that have been variably used in reference APWPs but that as a result of their low quality muted the real magnitude of the Jurassic monster shift. Finally, we provide paleocontinental reconstructions to describe examples of the bold signature that the monster polar shift left in the distribution of climate‐sensitive sedimentary facies worldwide. Key Points: We review the status of the Jurassic apparent polar wander path, which has long been controversialWe show with new data that the widely used paleomagnetic poles from the Morrison Formation of the Colorado Plateau are overprintedWe provide paleomagnetic poles from Adria, promontory of Africa, that confirm the Jurassic monster shift, a major candidate for true polar wander [ABSTRACT FROM AUTHOR]

Several types of pathological bony overgrowth are known from various dinosaur taxa but, except for stress fractures, are rarely reported from appendicular elements. Herein we describe pathological manual and pedal phalanges of a camarasaurid sauropod (SMA 0002), which show features rarely recognised in non-avian dinosaurs. They include lateral osteophytes and smoothing of phalangeal articular surfaces, a deep pit, proximal enthesophytes in pedal unguals, distal overgrowth associated with a fracture, and a knob-like overgrowth lateral to the distal condyles of a pedal phalanx. Their causes were assessed by means of visual examination, CT scans, and bone histology, where possible. The lateral osteophytes are interpreted as symptoms of osteoarthritis. The ossified tendon insertions in the unguals are most probably the result of prolonged, heavy use of the pedal claws, possibly for scratchdigging. The distal overgrowth is interpreted to have developed due to changed stress regimes, and to be the cause for the fracture. The deep pit represents most likely a case of osteochondrosis, whereas the knob-like overgrowth likely represents a post-traumatic phenomenon not previously reported in dinosaurs. The study confirms that a rigorous assessment of pathologies can yield information about behaviour in long-extinct animals.

A set of associated left pedal elements of a sauropod dinosaur from the Upper Jurassic Morrison Formation in Weston County, Wyoming, is described here. Several camarasaurids, a nearly complete small brachiosaur, and a small diplodocid have been found at this locality, but none match the exceptionally large size of the pedal elements. Next to the associated pedal elements, an isolated astragalus, phalanx and ungual were found, which match the large metatarsals in size. The elements cannot be ascribed to diplodocids due to the lack of a ventral process of metatarsal I. Moreover, the morphology of metatarsal V has a broad proximal end, with a long and narrow distal shaft, which differs from Camarasaurus. The size of the material and a medially beveled distal articular surface of metatarsal IV imply an identification as a brachiosaurid. This is the largest pes ever reported from a sauropod dinosaur and represents the first confirmed pedal brachiosaur elements from the Late Jurassic of North America. Furthermore, this brachiosaur material (the pes and the small nearly complete specimen) is the northernmost occurrence of brachiosaurids in the Morrison Formation.

A set of associated left pedal elements of a sauropod dinosaur from the Upper Jurassic Morrison Formation in Weston County, Wyoming, is described here. Several camarasaurids, a nearly complete small brachiosaur, and a small diplodocid have been found at this locality, but none match the exceptionally large size of the pedal elements. Next to the associated pedal elements, an isolated astragalus, phalanx and ungual were found, which match the large metatarsals in size. The elements cannot be ascribed to diplodocids due to the lack of a ventral process of metatarsal I. Moreover, the morphology of metatarsal V has a broad proximal end, with a long and narrow distal shaft, which differs from Camarasaurus. The size of the material and a medially beveled distal articular surface of metatarsal IV imply an identification as a brachiosaurid. This is the largest pes ever reported from a sauropod dinosaur and represents the first confirmed pedal brachiosaur elements from the Late Jurassic of North America. Furthermore, this brachiosaur material (the pes and the small nearly complete specimen) is the northernmost occurrence of brachiosaurids in the Morrison Formation. [ABSTRACT FROM AUTHOR]

Thin hydrocarbon reservoir facies pose resolution challenges and waveform-signature opportunities in seismic reservoir characterization and prospect identification. In this study, we present a case study, where instantaneous frequency variation in response to a thin hydrocarbon pay zone is analyzed and integrated with other independent information to explain drilling results and optimize future drilling decisions. In Morrison NE Field, some wells with poor economics have resulted from well-placement incognizant of reservoir heterogeneities. The study area in Clark County, Kanas, USA, has been covered by a surface 3D seismic reflection survey in 2010. The target horizon is the Viola limestone, which continues to produce from 7 of the 12 wells drilled within the survey area. Seismic attributes extraction and analyses were conducted with emphasis on instantaneous attributes and amplitude anomalies to better understand and predict reservoir heterogeneities and their control on hydrocarbon entrapment settings. We have identified a higher instantaneous frequency, lower amplitude seismic facies that is in good agreement with distinct lithofacies that exhibit better (higher porosity) reservoir properties, as inferred from well-log analysis and petrographic inspection of well cuttings. This study presents a pre-drilling, data-driven approach of identifying sub-resolution reservoir seismic facies in a carbonate formation. This workflow will assist in placing new development wells in other locations within the area. Our low amplitude high instantaneous frequency seismic reservoir facies have been corroborated by findings based on well logs, petrographic analysis data, and drilling results. [ABSTRACT FROM AUTHOR]

Diplodocids are among the best known sauropod dinosaurs. Numerous specimens of currently 15 accepted species belonging to ten genera have been reported from the Late Jurassic to Early Cretaceous of North and South America, Europe, and Africa. The highest diversity is known from the Upper Jurassic Morrison Formation of the western United States: a recent review recognized 12 valid, named species, and possibly three additional, yet unnamed ones. One of these is herein described in detail and referred to the genus Galeamopus. The holotype specimen of Galeamopus pabsti sp. nov., SMA 0011, is represented by material from all body parts but the tail, and was found at the Howe-Scott Quarry in the northern Bighorn Basin in Wyoming, USA. Autapomorphic features of the new species include a horizontal canal on the maxilla that connects the posterior margin of the preantorbital and the ventral margin of the antorbital fenestrae, a vertical midline groove marking the sagittal nuchal crest, the presence of a large foramen connecting the postzygapophyseal centrodiapophyseal fossa and the spinopostzygapophyseal fossa of mid- and posterior cervical vertebrae, a very robust humerus, a laterally placed, rugose tubercle on the concave proximal portion of the anterior surface of the humerus, a relatively stout radius, the absence of a distinct ambiens process on the pubis, and a distinctly concave posteroventral margin of the ascending process of the astragalus. In addition to the holotype specimen SMA 0011, the skull USNM 2673 can also be referred to Galeamopus pabsti. Histology shows that the type specimen SMA 0011 is sexually mature, although neurocentral closure was not completed at the time of death. Because SMA 0011 has highly pneumatized cervical vertebrae, the development of the lamination appears a more important indicator for individual age than neurocentral fusion patterns. SMA 0011 is one of very few sauropod specimens that preserves the cervico-dorsal transition in both vertebrae and ribs. The association of ribs with their respective vertebrae shows that the transition between cervical and dorsal vertebrae is significantly different in Galeamopus pabsti than in Diplodocus carnegii or Apatosaurus louisae, being represented by a considerable shortening of the centra from the last cervical to the first dorsal vertebra. Diplodocids show a surprisingly high diversity in the Morrison Formation. This can possibly be explained by a combination of geographical and temporal segregation, and niche partitioning.

Recently developed data collection techniques allow for improved characterization of sedimentary outcrops. Here, we outline a workflow that utilizes unmanned aerial vehicles (UAV) and structure-from-motion (SfM) photogrammetry to produce sub-meter-scale outcrop reconstructions in 3-D. SfM photogrammetry uses multiple overlapping images and an image-based terrain extraction algorithm to reconstruct the location of individual points from the photographs in 3-D space. The results of this technique can be used to construct point clouds, orthomosaics, and digital surface models that can be imported into GIS and related software for further study. The accuracy of the reconstructed outcrops, with respect to an absolute framework, is improved with geotagged images or independently gathered ground control points, and the internal accuracy of 3-D reconstructions is sufficient for sub-meter scale measurements. We demonstrate this approach with a case study from central Utah, USA, where UAV-SfM data can help delineate complex features within Jurassic fluvial sandstones. [ABSTRACT FROM AUTHOR]

Recent construction at the Moab Giants dinosaur museum property ~ 10 miles (~ 16 km) north of Moab, in Grand County, Utah in 2014–2015 revealed a number of moderately well preserved dinosaur tracks from the Upper Jurassic, Salt Wash Member of the Morrison Formation. The best specimens were preserved as natural casts on the underside of massive sandstone beds, many containing dense assemblages of invertebrate traces. Here we describe several tridactyl theropod tracks, an ornithischian manus attributable to ichnogenus Stegopodus and an ornithischian pes track attributed to ichnogenus Deltapodus . Variably preserved Deltapodus have now been reported from the Tidwell, Salt Wash and Brushy Basin members of the Morrison Formation from Garfield, Grand and San Juan counties respectively, suggesting a wide distribution in space and time. The Salt Wash specimen is considered to be the most representative of Deltapodus morphologies reported from large samples in other regions, notably in Spain, Portugal western China and North Africa. Differences between Stegopodus and Deltapodus are reviewed. Deltapodus is reported from Europe and Asia as well as North America, in the Middle Jurassic through Late Cretaceous, and is often represented by abundant trackways. Stegopodus is presently reported from the Jurassic where it occurs in the Late Jurassic of North America as isolated tracks, and, with some debate, as trackways and isolated tracks from Europe. A middle Jurassic occurrence from Morocco is also reported. [ABSTRACT FROM AUTHOR]

Nearly 150 occurrences of turtles and neosuchian crocodyliforms in the Upper Jurassic Morrison Formation indicate that, by number of localities and number of specimens, both are preferentially preserved off the Colorado Plateau in deposits in the eastern and northern parts of the Morrison basin, suggesting that these latter areas contained wetter paleoenvironments and either were more populated with these semi-aquatic taxa or more frequently preserved their remains, compared with areas to the south and west. Cursorial crocodylomorphs occur at more sites and in greater numbers on the Colorado Plateau than to the east and north, but this pattern is only significant by number of specimens. Previous suggestions of wetter paleoenvironmental conditions on floodplains distal to the southwestern source areas on the Colorado Plateau, or western source areas for northern outcrops, based on geological and microvertebrate data, seem to be borne out by these data from semi-aquatic mesovertebrates. [ABSTRACT FROM AUTHOR]