Morrison formation

The Upper Jurassic Morrison Formation of western North America has yielded a number of specimens assigned to the ornithischian dinosaurs Stegosaurus and Camptosaurus, and many of these specimens come from channel sandstone deposits. Six new specimens are recorded mostly from channel sandstones as well. Indeed, early analyses of site occurrences (reducing the effects of large single-site samples) suggested that Stegosaurus and Camptosaurus were more often found in channel sandstone deposits than other common Morrison Formation dinosaurs such as Camarasaurus or Diplodocus. This also indicated the possibility of ecological segregation of the former two genera from other herbivorous dinosaurs of the Morrison. Revisiting this question with additional data suggests the pattern may not be as strong as it once appeared. Analysis of occurrence data indicates that Stegosaurus and Camptosaurus occur in channel sandstone deposits slightly more frequently than the two sauropods, but statistical analysis of this pattern by either localities or individuals indicates little significance to the trend. However, Camptosaurus appears more strongly associated with channel sandstone deposits relative to other dinosaurs than does Stegosaurus. These results suggest that any ecological segregation of these genera was moderate, but that, if present, the segregation was more pronounced in Camptosaurus.

A new specimen of the theropod dinosaur Torvosaurus tanneri discovered by Elmer Riggs in 1899 in the Freezeout Hills of Wyoming and held in the Field Museum of Natural History is described. This specimen demonstrates that unreported material of this species has been present in museum collections 80 years prior to the species' scientific description and it likely represents the first non-dental material of this species to be collected. This material comprises parts of the left foot and right hand, including phalanges which were previously unknown for Torvosaurus, and substantiates the possibility that other Torvosaurus material may be undiscovered in museum collections. Its occurrence in a multitaxon quarry is consistent with other skeletal finds of Torvosaurus, all or most of which occur in association with other, more common Morrison dinosaur taxa.

Abstract—The Fruita Paleontological Research Natural Area (FPA) is remarkable for the abundance and diversity of
Upper Jurassic terrestrial fossils preserved within an area of approximately one square kilometer. Taking advantage of
the three-dimensional outcrop at the FPA, high-resolution event stratigraphic methodologies have been used to correlate
the crevasse splays (flood deposits) and to evaluate the interrelationships of individual fossil sites to each other and
to specific local environments. These include: (1) bank-controlled, gravelly, low-sinuosity river channels (ribbon
sandstones facies), (2) clay-dominated levees with well-sorted, sandstone, proximal crevasse-splay complexes best
developed at channel bends (levee facies), (3) drab, poorly-drained, alkaline flood plains with carbonate-cemented
crevasse splays and poorly-developed paleosols (drab flood-plain facies), (4) well-oxidized, well-drained flood plains
having well-developed paleosols with nodular carbonates (dark red flood-plain facies), (5) relatively permanent springfed
ponds or marshes locally overlying channel thalwegs (pond/marsh facies), and (6) ephemeral alkaline flood-plain
ponds characterized by barite nodules (alkaline pond facies). The distribution of active and abandoned channel-levee
complexes controlled depositional base level within the flood-plain environments. The facies defining these environments
also preserved distinctive suites of fossils: (1) ribbon sandstone facies preserve large dinosaurs, aquatic crocodilians,
turtles, unionid bivalves, and isolated logs, (2) levee facies preserve dinosaur bones and diverse trace fossils,
(3) drab flood-plain facies preserve evidence of dinosaur nests, diverse small terrestrial vertebrates, and diverse trace
fossils associated with crevasse splays, (4) dark red flood-plain facies do not preserve significant body fossils, but
preserve abundant root traces and other trace fossils, (5) pond/marsh facies preserve abundant carbonaceous plant
materials, logs, aquatic invertebrates, fish, and dinosaurs, and (6) alkaline pond facies preserve small delicate fossils
washed in from across the flood plain, including invertebrates, fish scales, and small terrestrial vertebrate fossils
(many with intact skeletons). The conceptual framework described herein forms a basis for further research on the
extraordinary natural laboratory preserved within the Morrison Formation at the FPA.

A new taxon of diplodocid sauropod, Kaatedocus siberi gen. et sp. nov., is recognized based on well-preserved cervical vertebrae and skull from the Morrison Formation (Kimmeridgian, Late Jurassic) of northern Wyoming, USA. A phylogenetic analysis places it inside Diplodocinae (Sauropoda: Flagellicaudata: Diplodocidae), as a sister taxon to a clade uniting Tornieria africana and the classical diplodocines Barosaurus lentus and Diplodocus. The taxon is diagnosed by a unique combination of plesiomorphic and derived traits, as well as the following unambiguous autapomorphies within Diplodocidae: frontals separated anteriorly by a U-shaped notch; squamosals restricted to the post-orbital region; presence of a postparietal foramen; a narrow, sharp and distinct sagittal nuchal crest; the paired basal tuber with a straight anterior edge in ventral view; anterior end of the prezygapophyses of mid- and posterior cervical vertebrae is often an anterior extension of the pre-epipophysis, which projects considerably anterior to the articular facet; anterodorsal corner of the lateral side of the posterior cervical vertebrae marked by a rugose tuberosity; posterior margin of the prezygapophyseal articular facet of posterior cervical vertebrae bordered posteriorly by conspicuous transverse sulcus; posterior cervical neural spines parallel to converging. The inclusion of K. siberi and several newly described characters into a previously published phylogenetic analysis recovers the new taxon as basal diplodocine, which concurs well with the low stratigraphical position of the holotype specimen. Dinheirosaurus and Supersaurus now represent the sister clade to Apatosaurus and Diplodocinae and therefore the most basal diplodocid genera. The geographical location in the less known northern parts of the Morrison Fm., where K. siberi was found, corroborates previous hypotheses on faunal provinces within the formation. The probable subadult ontogenetic stage of the holotype specimen allows analysis of ontogenetic changes and their influence on diplodocid phylogeny. http://zoobank.org/urn:lsid:zoobank.org:pub:70181793-AA2D-4F14-BAD2-F12B9D095B3D

Although diplodocoid sauropods from Africa and the Americas are well known, their European record remains largely neglected. Here we redescribe Dinheirosaurus lourinhanensis from the Late Jurassic of Portugal. The holotype comprises two posterior cervical vertebrae, the dorsal series and a caudal centrum. Redescription demonstrates its validity on the basis of three autapomorphies:(1) posteriorly restricted ventral keel on posterior cervical vertebrae;(2) three small subcircular fossae posterior to the lateral coel ...

Four isolated sauropod axial elements from the Oxford Clay Formation (Callovian, Middle Jurassic) of Peterborough, UK, are described. Two associated posterior dorsal vertebrae show a dorsoventrally elongated centrum and short neural arch, and nutrient or pneumatic foramina, most likely belonging to a non-neosauropod eusauropod, but showing ambiguous non-neosauropod eusauropod and neosauropod affinities. An isolated anterior caudal vertebra displays a ventral keel, a ‘shoulder’ indicating a wing-like transverse process, along with a possible prespinal lamina. This, together with an overall high complexity of the anterior caudal transverse process (ACTP) complex, indicates that this caudal could have belonged to a neosauropod. A second isolated middle-posterior caudal vertebra also shows some diagnostic features, despite the neural spine and neural arch not being preserved and the neurocentral sutures being unfused. The positioning of the neurocentral sutures on the anterior one third...

Clay minerals are some of the most interesting and variable aspects of the lithology of the Morrison
Formation. Clays have been utilized for many diverse applications, including paleoenvironmental analyses and
temporal correlations. The chemical nature of clay minerals, however, allows them to be easily influenced by
environmental conditions, both immediately after deposition and over the millions of years of burial. This study
looks at the clay mineralogy of the Morrison Formation using X-ray diffraction analysis, and concludes that: (1)
the clay mineralogy of the Morrison Formation is highly variable, both laterally and vertically; and (2) there
does not appear to be a consistently developed horizon of clay change from illitic to smectitic clays. As a result
of these findings, caution is urged in using clay minerals for correlative purposes or as paleoenvironmental
indicators.

In 2016 and 2017, the Utah Geological Survey partnered with the U.S. Bureau of Land Management to conduct a paleontological inventory of the Morrison Formation south and west of Blanding, Utah, along the eastern margin of the Bears Ears National Monument. The Morrison in this region is critical to understanding Upper Jurassic stratigraphy across the Colorado Plateau because it is the type area for the Bluff Sandstone, Recapture, Westwater Canyon, and Brushy Basin Members of the Morrison Formation, which are the basis for nomenclature in New Mexico and Arizona as well. Researchers have disagreed about nomenclature and correlation of these units, which transition northward in the study area into the Tidwell, Salt Wash, and Brushy Basin Members. Numerous vertebrate localities make inclusion of the Bluff Sandstone and Recapture Members in the Middle Jurassic San Rafael Group, as suggested by some previous workers, unlikely. The Salt Wash Member does not separate the Bluff Sandstone and ...

A screenwashed microvertebrate site, the Mile 175 locality, in the Morrison Formation of Wyoming has yielded more than 3000 elements of actinopterygian fish and indicates that fish were not as rare in some parts of the formation as previously supposed. Actinopterygians are represented by diverse teeth and tooth-bearing bone fragments, fin elements, and thousands of scales and scale fragments that can be divided into three distinct morphotypes. Lungfish are rare, represented by nine toothplates and toothplate fragments that are provisionally assigned to Potamoceratodus. Tetrapods recovered from the Mile 175 locality include indeterminate salamanders, turtles, choristoderes, a squamate, goniopholid crocodyliforms, theropod and ornithopod dinosaurs, and several mammals, including Docodon and indeterminate multituberculates. Salamanders are represented by just a few indeterminate vertebrae. The turtle fauna includes numerous small shell fragments and limb elements. The authors assign a tooth-bearing jaw fragment and several vertebrae to the choristodere Cteniogenys, whereas a sole vertebra is the only squamate fossil recovered. Theropod dinosaurs are well represented by several teeth, as is the ornithopod dinosaur Othnielosaurus. Similarly, several mammalian tooth and jaw fragments can be referred to either Docodon or Multituberculata indet. Dominance of the sample by aquatic and semi-aquatic taxa suggests the paleodepositional environment was a permanent water source. Many of the specimens appear to represent small and presumably ontogenetically young individuals of larger, known taxa in the Morrison Formation, and the site includes the northernmost occurrences of several taxa in the formation. Screenwashing efforts at several other previously quarried large-vertebrate sites in the Morrison Formation have shown promising results for recovering previously unidentified taxa.

Palaeopathology is important as it provides remarkable insights into the lifestyles of dinosaurs and other prehistoric animals. The Late Jurassic Allosaurus known as Big Al (MOR 693) from Big Horn County, Wyoming preserves at least 19 injuries. About 2% of all bones showed abnormalities, including osteomyelitis on the right foot, on the first phalanx of the third toe, which may have contributed to the animal's death. There would likely have been many more pathologies that did not make it into the paleontological record due do the lack of soft-tissue preservation. Analysis of MOR 693's immune response to bone infections and comparing it to other theropods, we can confidently say that dinosaurs possessed an immune system that isolated and localized infections like extant Aves. Institution Abbreviations MOR, Museum of the Rockies; UUVP, University of Utah Vertebrate Paleontology

ABSTRACT 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.

Small lakes are excellent records of environmental changes and are sensitive to local climate fluctuations. Large lacustrine systems record larger-scale climate events. Wetland deposits also provide high-resolution paleoclimatic and paleoenvironmental data. Although wetland deposits are typically associated with wet climatic conditions, they actually occur in a wide variety of climates. Whereas lakes and wetlands are very sensitive to changes in climate, high-resolution data in these archives are lost unless it is possible to differentiate these deposits from other “floodplain” deposits. Synthesis of micromorphological and geochemical data with facies relationships is critical to accurate interpretations of ancient wetland–lacustrine deposits. This study illustrates how micromorphology and geochemistry, combined with facies relationships, provide a viable method for differentiating complex, ancient wetland–lacustrine subenvironments. A hydrogeomorphological classification is propose...

Small lakes are excellent records of environmental changes and are sensitive to local climate fluctuations. Large lacustrine systems record larger-scale climate events. Wetland deposits also provide high-resolution paleoclimatic and paleoenvironmental data. Although wetland deposits are typically associated with wet climatic conditions, they actually occur in a wide variety of climates. Whereas lakes and wetlands are very sensitive to changes in climate, high-resolution data in these archives are lost unless it is possible to differentiate these deposits from other “floodplain” deposits. Synthesis of micromorphological and geochemical data with facies relationships is critical to accurate interpretations of ancient wetland–lacustrine deposits. This study illustrates how micromorphology and geochemistry, combined with facies relationships, provide a viable method for differentiating complex, ancient wetland–lacustrine subenvironments. A hydrogeomorphological classification is proposed to provide appropriate genetic terminology that is useful in the rock record. Eight Morrison Formation subenvironments within lacustrine depositional successions from north central Wyoming were delineated using this interdisciplinary approach. Subenvironments include shallow-water wetlands, marsh, lacustrine fringe, and fen basin and fringe deposits. Synthesized data indicate that an overall basinal infilling succession was punctuated by 3 major lake contraction events, which were followed by extended periods of landscape stability. Initially balance-filled conditions dominated the shallowing-upward lacustrine deposits such that sediment and water supply, and accommodation space were relatively equal. As the lake basin filled, shallower water, underfilled lake conditions prevailed. The distribution of wetland pedotypes indicates that evapotranspiration remained high, suggesting that a stable, semi-arid to arid climate dominated in this area throughout Morrison time. Also supporting a semi-arid to arid climate are more positive carbon isotopes compared to values for disseminated organic material in the surrounding area, abundant barite nodules, gypsum pseudomorphs, and zeolites. Although major fluctuations in lake level may have resulted from punctuated wetter episodes, synthesized data suggest that overall the climate remained relatively arid to semiarid and the lake basin remained closed throughout most of Morrison time. Fluctuations in lake level likely resulted from a significant increase in recharge in the source area, possibly related to volcanic events rather than a change in climate.

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.

Fission-track ages from a section through the Morrison Formation in central Utah show that most of the Morrison Formation is Late Jurassic or perhaps earliest Cretaceous, ranging in age from 130 to 157 Ma. However, tht: upper part of the Morrison Formation in the Brushy Basin Member gives ages ranging from 99 to 123 Ma, covering a wide span of Early Cretaceous time. The bentonites dated are st:ratigraphically below what has been called tbe basal Buckhorn Conglomerate Member of thl! Cedar Mountain Formation. This may indic~lte that (1) the Buckhorn Conglomerate is not the base of the Cedar Mountain age sediments;

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 N...

Palaeopathology is important as it provides remarkable insights into the lifestyles of dinosaurs and other prehistoric animals. The Late Jurassic Allosaurus known as Big Al (MOR 693) from Big Horn County, Wyoming preserves at least 19 injuries. About 2% of all bones showed abnormalities, including osteomyelitis on the right foot, on the first phalanx of the third toe, which may have contributed to the animal's death. There would likely have been many more pathologies that did not make it into the paleontological record due do the lack of soft-tissue preservation. Analysis of MOR 693’s immune response to bone infections and comparing it to other theropods, we can confidently say that dinosaurs possessed an immune system that isolated and localized infections like extant Aves.

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A left mandible of a small crocodyliform found in the Upper Jurassic Morrsion Formation of northeastern Wyoming represents the first occurrence of the atoposaurid Theriosuchus in North America. The specimen demonstrates lower jaw morphology, including heterodonty (as indicated by alveolus shape), similar to Theriosuchus and Knoetschkesuchus, but autapomorphies and a unique combination of characters among these taxa indicate that it is a distinct, new species of Theriosuchus.

In 2016 and 2017, the Utah Geological Survey partnered with the U.S. Bureau of Land Management to conduct a paleontological inventory of the Morrison Formation south and west of Blanding, Utah, along the eastern margin of the Bears Ears National Monument. The Morrison in this region is critical to understanding Upper Jurassic stratigraphy across the Colorado Plateau because it is the type area for the Bluff Sandstone, Recapture, Westwater Canyon, and Brushy Basin Members of the Morrison Formation, which are the basis for nomenclature in New Mexico and Arizona as well. Researchers have disagreed about nomenclature and correlation of these units, which transition northward in the study area into the Tidwell, Salt Wash, and Brushy Basin Members. Numerous vertebrate localities make inclusion of the Bluff Sandstone and Recapture Members in the Middle Jurassic San Rafael Group, as suggested by some previous workers, unlikely. The Salt Wash Member does not separate the Bluff Sandstone and Recapture Members at Recapture Wash, but sandstone lenses of Salt Wash facies occur higher in northern Recapture exposures. Northward, along the outcrop belt east of Comb Ridge, the Bluff-Recapture interval thins, interlenses, and pinches out into the Tidwell and lower Salt Wash, with the main lower sandstone interval of the Westwater Canyon merging northward into the upper Salt Wash Member.


The partly covered, 1938 type section of the Brushy Basin Member is identified along Elk Mountain Road at the southern end of Brushy Basin. We describe a detailed, accessible Morrison Formation reference section about 11.2 km (7 mi) to the south along Butler Wash. There, 81.68 m (268 ft) of Brushy Basin Member is well exposed along a road between the top of the Westwater Canyon Member and the base of the Lower Cretaceous Burro Canyon Formation. We informally call the upper sandstone bed(s) of the Westwater Canyon Member that cap mesas and benches in the region “No-Mans Island beds.” Smectitic mudstones between the No-Mans Island beds and the main sandstone body of the Westwater Canyon suggest that the Salt Wash-Brushy Basin contact to the north may be somewhat older than the base of the Brushy Basin Member as originally defined in its type area. Determining whether the No-Mans Island beds pinch out to the north or are removed by erosion below the regional basal Brushy Basin paleosol requires further research. Several significant fossil vertebrate and plant sites have been documented in the Brushy Basin type area. Newly identified volcanic ashes provided zircons for U-Pb ages of 150.67 ± 0.32 Ma from near the top of the Brushy Basin Member and of 153.7 ± 2.1 Ma and 153.8 ± 2.2 Ma for two zircons in lower part of Recapture Member. At the top of the Brushy Basin Member, ferruginous paleosols commonly overlying conglomeratic sandstone are speculated to be of Early Cretaceous age (detrital zircon age pending) and are assigned herein to the Yellow Cat Member of the Burro Canyon Formation. These iron-rich paleosols suggest wetter climatic conditions during the Jurassic-Cretaceous transition in the Blanding basin.

The ecosystem impact of megaherbivorous dinosaurs of the Morrison Formation would have depended on their abundance (number of animals per unit of habitat area) on the landscape. We constrain Morrison megaherbivore abundance by modelling dinosaur abundance in terms of carrying capacity (K), average body mass (ABM) and animal’s energy needs. Two kinds of model are presented: ‘demand-side’ models that estimate K in terms of the aggregate energy demand of the dinosaur community, and ‘supply-side’ models that estimate K in terms of retrodicted primary productivity. Baseline values of K, ABM and energy needs for the models are further derived from comparisons with modern large herbivores, and from the composition of the megaherbivore fauna from a particular stratigraphic interval of the Morrison, but in all models a broad range of fractions and multiples of these baseline parameters are considered. ‘Best-guess’ estimates of Morrison megaherbivore abundance suggest an upper limit of a few ...

The Mygatt-Moore Quarry is a deposit of several thousand dinosaur bones in the Brushy Basin Member of the Morrison Formation in western Colorado. The site has been worked for nearly 30 years and many specimens have been collected. This study gathered data about the quarry from many sources to investigate the origins of the deposit. The Mygatt-Moore Quarry appears to be an attritional, delayed-burial deposit of a relatively restricted diversity of dinosaurs, with few other non-dinosaurian taxa, that accumulated in a pond deposit in an overbank setting. The entire excavated quarry is currently at approximately 550 m2. More than 2300 mapped bones occur in a layer approximately 1 m thick, and more than 58% of observed bones are in the lower 33 cm of the deposit. Drill cores indicate that the extent of the deposit runs 80–100 m west and southwest and may cover at least a total of 4100 m2. Clay clasts, rare rock fragments, and abundant calcium carbonate nodules at the base of the deposit were washed in, and REE analysis indicates that the nodules may have originated from two sources. A U/Pb date, calculated from zircons identified in a mudstone sample collected from the bone layer, gave an age of 152.18 Ma +/-0.29 Ma, making the quarry approximately the same age as Reed’s Quarry 9 at Como Bluff. Plants identified from the site include abundant Equisetum and conifer wood, plus Isoetaceae, Czekanowskia, Ginkgo, ferns such as Coniopteris, and conifers such as Brachyphyllum. The gastropod Viviparus reesidei has been identified at the base of the deposit. Vertebrate fossils include several small, indeterminate reptiles, a goniopholidid crocodylomorph, and the dinosaurs Ceratosaurus, Allosaurus, Apatosaurus, Camarasaurus, Mymoorapelta, Othnielosaurus, and an indeterminate diplodocine (cf. Diplodocus or Barosaurus). The bone layer is dominated by skeletal remains of Allosaurus and Apatosaurus, with other dinosaur taxa much more rare. The MNI is 22, and the sample is mostly adults, with several juveniles and one sub-adult. Shed theropod teeth are very abundant (N = 419), and 97.6% of identifiable teeth belong to Allosaurus (only 9 have been positively attributed to Ceratosaurus). Most of the sample consists of teeth, vertebrae, ribs, and fragments; cranial and other elements are less abundant but are not unusually so – observed abundances are close to expected values based on numbers in a single skeleton. Voorhies group analysis suggests that identifiable material is semi-autochthonous and is neither winnowed nor transported in to the area. Material at the site is almost universally disarticulated. The rate of articulation ( 0.337%) is the lowest among eight major quarries of the Morrison Formation that were analyzed; only Cleveland-Lloyd was close (1.98%). Taphonomic modifications include trampling breaks, abundant corrosion, and tooth marks; degrees of weathering and abrasion were low. Bones from the site seem to have had two main sources: the better preserved, identifiable elements seem to have been from the local area and were semi-autochthonous, whereas a “background” component of small, rounded bone fragments in densities up to 100/m3 were allochthonous and probably transported in to the site some distance. Most of these small fragments are about 5 cubic centimeters in volume, with a mean of 6.78 cc and a maximum in the excavated test meter of 45+ cc. Histological samples of representative bones indicate that preservation of osteons ranges from moderate (micro-fractured) to pristine even among the allochthonous bone fragment component of the quarry, suggesting that these elements may derive from multiple sources as well. Rose diagrams plotting the azimuths of 508 long bones show no preferred orientation to the material. Preservation of abundant plant material throughout the bone layer indicates that acidic soil conditions were common at the time; preservation of at least five patches of carbonized dinosaur skin and skin impressions suggests the possibility of dyoxic conditions in the soil as well. The Cleveland-Lloyd Quarry, otherwise a close correlate of the Mygatt-Moore Quarry, demonstrates significant differences upon close inspection. Large quarries in fine-grained facies in the Morrison Formation possess a very different preservation mode and profile from those in coarser sediments, which suggests that more may be learned in the future from study of large quarries in mudstones.

Mygatt-Moore Quarry in the Brushy Basin Member of the Upper Jurassic Morrison Formation is one of the more important large
dinosaur quarries in the formation, yielding fossils of sauropod dinosaurs including Apatosaurus, Camarasaurus, and an indeterminate diplodocine (cf. Diplodocus or Barosaurus), the theropod dinosaurs Allosaurus and Ceratosaurus, and the ornithischians Othnielosaurus and Mymoorapelta. Fossil wood and carbonized plants are known from the deposit, and carbonized dinosaur skin has also been discovered.

We report here on a new U/Pb radiometric age for the Mygatt-Moore Quarry, from a smectitic mudstone collected at the quarry horizon. We isolated zircons using an ultrasonic separation technique and standard heavy liquid and magnetic methods, analyzed single zircons using a chemical abrasion method (CA-TIMS). The age determined for this dinosaur quarry, 152.18 ±0.29 Ma, places the quarry at the boundary between the Kimmeridgian and Tithonian stages of the Late Jurassic Period. This age can now be used to place the quarry into stratigraphic position with respect to other dated horizons in the Morrison Formation and other rock units worldwide. We will also use this age along with other ages to create a radiometrically based stratigraphic framework for the Morrison Formation.

A bentonitic ash bed 8.7 m below the top of the Upper Jurassic Morrison Formation near Hanksville, Utah, has been dated by laser ablation multi-collector inductively coupled plasma mass spectrometry and gives a single-crystal U-Pb zircon age of 149.0 +2.5/-2.2 Ma. This age is statistically the same as the 149.3 ± 0.5 Ma age of an ash bed located 0.5 m below the top of the Brushy Basin Member of the Morrison Formation near Notom, Utah, about 25 km to the west. The Hanksville section has a short section of possible Cedar Mountain Formation (between 0.4 and 7.3 m thick) on top of the Morrison section. Two young contaminant zircons with a peak age of 122.5 Ma in the Brushy Basin ash sample indicate that the Cedar Mountain sediments present here are from the lowermost part of the Cedar Mountain Formation. b b b

The Upper Jurassic Morrison Formation of western North America has yielded a number of specimens assigned to the ornithischian dinosaurs Stegosaurus and Camptosaurus, and many of these specimens come from channel sandstone deposits. Six new specimens are recorded mostly from channel sandstones as well. Indeed, early analyses of site occurrences (reducing the effects of large single-site samples) suggested that Stegosaurus and Camptosaurus were more often found in channel sandstone deposits than other common Morrison Formation dinosaurs such as Camarasaurus or Diplodocus. This also indicated the possibility of ecological segregation of the former two genera from other herbivorous dinosaurs of the Morrison. Revisiting this question with additional data suggests the pattern may not be as strong as it once appeared. Analysis of occurrence data indicates that Stegosaurus and Camptosaurus occur in channel sandstone deposits slightly more frequently than the two sauropods, but statistical ...

In the summer of 1878, American paleontologist Edward Drinker Cope published the discovery of a sauropod dinosaur that he named Amphicoelias fragillimus. What distinguishes A. fragillimus in the annals of paleontology is the immense magnitude of the skeletal material. The single incomplete dorsal vertebra as reported by Cope was a meter and a half in height, which when fully reconstructed, would make A. fragillimus the largest vertebrate ever. After this initial description Cope never mentioned A. fragillimus in any of his scientific works for the remainder of his life. More than four decades after its description, a scientific survey at the American Museum of Natural History dedicated to the sauropods collected by Cope failed to locate the remains or whereabouts of A. fragillimus. For nearly a century the remains have yet to resurface. The enormous size of the specimen has generally been accepted despite being well beyond the size of even the largest sauropods known from verifiable...

Redescription of a trackway from the Salt Wash Member of the Morrison Formation (Upper Jurassic) in eastern Utah and comparisons with other tracks known from the Jurassic and Cretaceous of the region and the Late Jurassic globally indicate that the large theropod ichnogenus Hispanosauropus Mensink and Mertmann, 1984, previously known only from Europe, occurs also in the Morrison Formation. Hispanosauropus is distinct from Megalosauripus and most likely was made by an allosauroid theropod, although the possibility that it was made by a spinosauroid (torvosaurid) or a ceratosauroid cannot be ruled out. Close geographic and stratigraphic association of Hispanosauropus with the large theropod body fossil taxa Allosaurus, Torvosaurus, and Ceratosaurus in both North America and the Iberian Peninsula strengthens the case for the track's having been made by one of these genera. Megalosauripus appears to dominate large theropod track samples from the Entrada Sandstone through the base of the Morrison Formation (Tidwell Member); Hispanosauropus and similar tracks are most common in the Salt Wash Member and its equivalents, suggesting taxonomic turnover in the large theropod faunas during the early part of Morrison Formation deposition.

A new taxon of diplodocid sauropod, Kaatedocus siberi gen. et sp. nov., is recognized based on well-preserved cervical vertebrae and skull from the Morrison Formation (Kimmeridgian, Late Jurassic) of northern Wyoming, USA. A phylogenetic analysis places it inside Diplodocinae (Sauropoda: Flagellicaudata: Diplodocidae), as a sister taxon to a clade uniting Tornieria africana and the classical diplodocines Barosaurus lentus and Diplodocus. The taxon is diagnosed by a unique combination of plesiomorphic and derived traits, as well as the following unambiguous autapomorphies within Diplodocidae: frontals separated anteriorly by a U-shaped notch; squamosals restricted to the post-orbital region; presence of a postparietal foramen; a narrow, sharp and distinct sagittal nuchal crest; the paired basal tuber with a straight anterior edge in ventral view; anterior end of the prezygapophyses of mid-and posterior cervical vertebrae is often an anterior extension of the pre-epipophysis, which projects considerably anterior to the articular facet; anterodorsal corner of the lateral side of the posterior cervical vertebrae marked by a rugose tuberosity; posterior margin of the prezygapophyseal articular facet of posterior cervical vertebrae bordered posteriorly by conspicuous transverse sulcus; posterior cervical neural spines parallel to converging. The inclusion of K. siberi and several newly described characters into a previously published phylogenetic analysis recovers the new taxon as basal diplodocine, which concurs well with the low stratigraphical position of the holotype specimen. Dinheirosaurus and Supersaurus now represent the sister clade to Apatosaurus and Diplodocinae and therefore the most basal diplodocid genera. The geographical location in the less known northern parts of the Morrison Fm., where K. siberi was found, corroborates previous hypotheses on faunal provinces within the formation. The probable subadult ontogenetic stage of the holotype specimen allows analysis of ontogenetic changes and their influence on diplodocid phylogeny. http://zoobank.org/urn:lsid:zoobank.org:pub:70181793-AA2D-4F14-BAD2-F12B9D095B3D

A small sauropod dinosaur collected from the Rocky Mountains of central Colorado (north of the Elk Range, Pitkin County) is assigned to the rare genus Haplocanthosaurus. The specimen, MWC 8028, consists of four dorsal centra, five partial ribs, the sacrum, five caudal vertebrae, three chevrons, five partial neural spines and many fragments and  is from the lower third of the Upper Jurassic Morrison Formation. The dorsal vertebrae are procamerate, and on the sacral vertebrae the neural arch peduncles are vertically elongate and the neural spines are strongly reclined.  The only sauropod from the Morrison Formation that shares these characters is Haplocanthosaurus and based on those characters MWC 8028 is referred to Haplocanthosaurus.  This is at most the tenth specimen and the seventh locality for this sauropod, all within the Morrison Formation.

The Late Jurassic (157–150 Ma) Morrison Formation of the Western Interior of the United States contains abundant altered volcanic ash. On the Colorado Plateau, this formation accumulated behind and downwind of a subduction-related volcanic arc along the western margin of North America. The ash in these distal fallout tuffs probably drifted eastward from coignimbrite ash clouds related to collapse calderas. Altered volcanic ash is particularly abundant in the Brushy Basin Member of the upper part of the Morrison Formation. In one 110-m-thick section in eastern Utah, 35 separate beds were deposited in a 2.2 m.y. period. Alteration occurred when glassy volcanic ash fell into fl uvial and lacustrine environments, where it was diagenetically altered to various mineral assemblages but most commonly to smectitic clay. Periodically, ash fell into saline, alkaline lakes, and diagenetic alteration of the glassy ash produced a crudely zoned deposit on the Colorado Plateau. Altered volcanic ash beds in the outermost part of the lacustrine deposits are argillic (with smectitic clay), whereas zeolitic (clinoptilolite, analcime) and feldspathic (K-feldspar and albite) alteration dominates the interior zones. Feldspathic ash layers contain secondary silica, and consequently immobile element (e.g., Al, Ti, and high fi eld strength elements) abundances were strongly diluted in these rocks. In contrast, the argillic ash beds experienced strong SiO2 depletion, and, as a result, they are enriched in the relatively immobile elements. The compositions of the zeolitic ash beds are intermediate between these two extremes and experienced the least alteration. As a result of these changes, immobile element concentrations are less reliable than ratios for determining the original magmatic composition of the ash. Most of the altered ash (regardless of type) was also depleted in water-soluble elements like the alkalies, U, and V. The latter two elements were oxidized during diagenesis of the ash, became soluble, and were partially leached away by groundwater. Locally, U and V in groundwater were reduced upon contact with organic materials and formed important ore deposits. Several aspects of the mineralogy and geochemistry of the altered volcanic ash beds yield information about their original magmatic compositions. The volcanic ash beds typically have small phenoclasts of quartz, sanidine, plagioclase, biotite, zircon, apatite, and Fe-Ti oxides. Titanite is present in ~40% of the ash beds; pyroxene and amphibole were found in less than 5%. Phenocryst assemblages, mineral compositions, inferred high fO2, rare earth element patterns, and immobile element ratios all suggest the parent magmas for the altered tuffs were subduction-related dacites and rhyolites. Small numbers of tuffs have Fe-rich biotite, amphibole, and/or clinopyroxene; both pyroxene and amphibole are alkali rich. These tuffs lack titanite, but some contain anorthoclase and F-rich apatite. Combined with enrichments in Nb and Y, these features show some tuffs had an A-type character and were related to some type of within-arc extension. Paleowind directions, and distribution, radiometric ages, and compositions of the volcanic ash beds and of plutons in the western United States suggest that the most likely eruption sites were in the subduction-related Jurassic magmatic arc, which extended across western Utah and central Nevada and southward into the Mojave of California and southern Arizona (present-day coordinates). Pb isotopic compositions show that at least some of the ash was erupted from magma systems (now exposed as plutons) in the Mojave Desert. We conclude that a brief ignimbrite fl are-up from 157 to 150 Ma, but focused on the time period from 152 to 150 Ma, in this region may have been driven by slab steepening and conversion to a strike-slip boundary after a preceding phase of folding and thrusting. The presence of ash beds with A-type characteristics mixed with those that have more typical subduction signatures confirms that the Late Jurassic was a transitional time in North America when subduction was changing to transtensional movement along the western plate boundary.

The Morrison Formation in Utah and Colorado contams many volcanic ash layers and ashy beds, now altered rnostly to bentonite, that have yielded isotopic ages. The Brushy Basin Member. at the top of the formation, gives single-crystal. laser-fusion and step-heating, plateau 4 0~ r/3'~ r ages on sanidine that range systematically between 148.1 50.5 (1 std. error of mean) at the top of the nlember to 150.3 rt 0.3 Ma near the bottom. The Tidwell Member, at the base of the Morrison Formation, contaills one ash bed about 3 m above ...

In 2016 and 2017, the Utah Geological Survey partnered with the U.S. Bureau of Land Management to conduct a paleontological inventory of the Morrison Formation south and west of Blanding, Utah, along the eastern margin of the Bears Ears National Monument. The Morrison in this region is critical to understanding Upper Jurassic stratigraphy across the Colorado Plateau because it is the type area for the Bluff Sandstone, Recapture, Westwater Canyon, and Brushy Basin Members of the Morrison Formation, which are the basis for nomenclature in New Mexico and Arizona as well. Researchers have disagreed about nomenclature and correlation of these units, which transition northward in the study area into the Tidwell, Salt Wash, and Brushy Basin Members. Numerous vertebrate localities make inclusion of the Bluff Sandstone and Recapture Members in the Middle Jurassic San Rafael Group, as suggested by some previous workers, unlikely. The Salt Wash Member does not separate the Bluff Sandstone and ...

A left mandible of a small crocodyliform found in the Upper Jurassic Morrsion Formation of northeastern Wyoming represents the first occurrence of the atoposaurid Theriosuchus in North America. The specimen demonstrates lower jaw morphology, including heterodonty (as indicated by alveolus shape), similar to Theriosuchus and Knoetschkesuchus, but autapomorphies and a unique combination of characters among these taxa indicate that it is a distinct, new species of Theriosuchus.

As a result of recent updating of decay constants and standard ages used for 40Ar/39Ar dating, it is necessary
to recalibrate legacy ages obtained with older methods. These recalibrations bring legacy 40Ar/39Ar
ages into better agreement with ages obtained using 238U/206Pb dating methods. We present nine recalibrated
40Ar/39Ar ages for the Upper Jurassic Morrison Formation of the Western Interior, U.S.A., along with the
individual geographic and stratigraphic locations for each sample. These recalibrated ages will be useful
for researchers looking to place better age constraints on the flora and fauna of the Morrison Formation, as
well as for those working to understand stratigraphic relationships across the formation. The recalibrated
ages also can now be used reliably for comparisons with newer 238U/206Pb ages obtained for the Morrison
Formation.