We describe a microvertebrate assemblage from the J&M site, of the Upper Cretaceous (Campanian-Ma... more We describe a microvertebrate assemblage from the J&M site, of the Upper Cretaceous (Campanian-Maastrichtian) Williams Fork Formation. Breakdown of fossil bearing matrix was achieved with the use of heated dimethyl sulfoxide. Nine of the recovered taxa are new to both the J&M site and the Williams Fork Formation. The sharks Lonchidion griffisi, Chiloscyllium sp., and Cantioscyllium markaguntensis are the first non-batoid elasmobranchs reported from the Williams Fork Formation and are all represented by teeth. The rays Cristomylus and Psuedomyledaphus are also newly reported from teeth. The most common identifiable fossils were teeth of indeterminate amiids, most likely belonging to Melvius. Osteichthyan fossils new to the Williams Fork Formation include teeth of Paralbula, an indeterminate pycnodontid tooth plate fragment, and an indeterminate lungfish tooth fragment. A tooth of the teiid Peneteius is also the first reported from within the Williams Fork Formation. Alligatoroid teeth are relatively common and are extremely similar to those of the contemporaneous durophage Brachychampsa but are generically indeterminate. Terrestrial taxa were recovered in much smaller numbers. Theropod dinosaur fossils included isolated tooth fragments belonging to an indeterminate dromaeosaurid and, possibly, to Richardoestesia. We recovered both multituberculate and metatherian fossils in the form of isolated teeth. Some of these taxa are known from marine and estuarine deposits and, given that so many of these marine associated taxa have been recovered together, it seems likely that the J&M site is recording marine or estuarine influence within at least part of its depositional history. The mammalian taxa suggest a Judithian-Lancian age for the site, while records of the squamate Peneteius and the ray Myledaphus, suggest that the J&M site may be temporally transitional between other late Campanian and late Maastrichtian-aged localities.
The Morrison Formation contains a number of large quarries that have yielded dinosaurs and other ... more The Morrison Formation contains a number of large quarries that have yielded dinosaurs and other vertebrates, and many of these occur in sandstone beds representing ancient river channels. However, a number of very productive sites occur in mudstone beds representing other environments such as ephemeral ponds, and some of these yield both large dinosaurs and microvertebrates; these localities in mudstone beds represent different taphonomic modes of preservation and often preserve vertebrate taxa in different relative abundances from the channel sandstone sites. Among these important and very productive mudstone localities are the Cleveland-Lloyd Quarry, the Mygatt-Moore Quarry, and the microvertebrate sites of the Fruita Paleontological Area, and each of these preserves distinct vertebrate paleofaunas, different from sandstone sites and from each other, suggesting that mudstone localities had a very different mode of sampling the local biotas than did sites in sandstone.
New data related to the definition of the Oxfordian/Kimmeridgian boundary obtained mostly after 2... more New data related to the definition of the Oxfordian/Kimmeridgian boundary obtained mostly after 2006 are discussedi.e. after the proposal for the uniform boundary of the stages at the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland has been given. This boundary is based on the Subboreal-Boreal ammonite successions-where it is distinguished at the base of the Subboreal Baylei Zone which is defined by the Pictonia flodigarriensis horizon, and which corresponds strictly to the base of the Boreal Bauhini Zone. This boundary is defined also by other stratigraphical data-both palaeontological, geochemical and palaeomagnetical (including its well defined position close to the boundary between magnetozones F3n, and F3r-the latter corresponding to marine magnetic anomaly M26r). The boundary and the section are thus proposed as the GSSP for the Oxfordian/Kimmeridgian boundary. The boundary is well recognizable also in other sections of Subboreal and Boreal areas as discussed in the study, including southern England,
Vertebrate tracks are comparatively rare in Tertiary deposits of the western United States. Unlik... more Vertebrate tracks are comparatively rare in Tertiary deposits of the western United States. Unlike the deposits of the Mesozoic in this region, in which each formation often has several dozen known tracksites, there are only a few known sites in Paleocene units of the region (Lockley and Hunt, 1995), and though the Eocene Green River Formation contains relatively numerous tracks, especially those of birds, there are only a few taxa represented. The occurrence of amphibian tracks in the Eocene Wasatch Formation is therefore of interest, not only in that it adds to the known ichnological record of the Tertiary of the western United States but also in that the tracks indicate the presence of an otherwise under-represented member of the vertebrate paleofauna of the time. Skeletal remains of amphibians are present but not common in many Tertiary formations of the western United States, and remains of large salamanders are rare. Only the large caudate Piceoerpeton is known from the Tiffanian and Clarkforkian of Montana and Wyoming (Naylor and Krause, 1981), and its only Wasatchian occurrence is at Ellesmere Island, north of the Arctic Circle. The tracks described here appear to represent a nearly Piceoerpeton-sized salamander in the lacustrine shoreline deposits of the early Eocene Wasatch Formation of southwestern Wyoming.
... However, Batrachopus foot-prints might be confused with synapsid footprints in some cases (Sc... more ... However, Batrachopus foot-prints might be confused with synapsid footprints in some cases (Schultz-Pittman ... mammal prints and are thought to have been made by a mammal-like reptile (?therapsid)). ... structures found in GS-ENM are not as well preserved as tracks from some ...
The famous bone beds of the Morrison Formation, whose rocks are exposed from Wyoming down through... more The famous bone beds of the Morrison Formation, whose rocks are exposed from Wyoming down through the red rock region of the American Southwest, have yielded one of the most complete pictures of any ancient vertebrate ecosystem in the world. After more than a century of exploration, the Morrison continues to yield new discoveries about a time so different from our own that it almost seems imaginary. Aimed at the general reader, Jurassic West tells the story of the life of this ancient world as scientists have so far been able to reconstruct it. The book recounts the discovery of many important Late Jurassic dinosaurs such as Apatosaurus, Allosaurus, and Stegosaurus. But dinosaurs comprise barely a third of the more than 90 types of vertebrates known from the Formation, which include crocodiles and turtles, frogs and salamanders, dinosaurs and mammals, clams and snails, and ginkgoes, ferns, and conifers.
... collected from there by Museum of Geology crews in 1980 and again in 199 1. Most of the mater... more ... collected from there by Museum of Geology crews in 1980 and again in 199 1. Most of the material comes from the middle of the Morrison undifferentiated and ... The fos-sil-bearing layer is approximately 1 meter thick and occurs immediately above a thin, lenticular sandstone unit ...
The Mygatt-Moore Quarry is a deposit of several thousand dinosaur bones in the Brushy Basin Membe... more 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 more than 30 years and nearly 2400 mapped specimens have been collected. This study gathered data about the quarry from many sources to investigate the origin of the deposit. The Mygatt-Moore Quarry appears to be an attritional deposit of a relatively restricted diversity of dinosaurs, with few other non-dinosaurian taxa, that accumulated in a vernal pool deposit in an overbank setting. Bone modification was mostly by corrosion and breakage by trampling; scavenging was abundant. The paleofauna is dominated by Allosaurus and Apatosaurus (MNI and NIS), with the polacanthid ankylosaur Mymoorapelta less common. The matrix of the main quarry layer includes abundant carbonized fragments of plant material, and the mud during the time of deposition may have been often at least damp and occasionally acidic and dysoxic. ...
The Upper Jurassic Morrison Formation of western North America has yielded a number of specimens ... more 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 ...
A trilobite pygidium, likely referable to the genus Bonnima, is the first evidence of a member of... more A trilobite pygidium, likely referable to the genus Bonnima, is the first evidence of a member of the Corynexochida reported from the Lower Cambrian (Dyeran Stage) Chambless Limestone of the southern Marble Mountains in the Mojave Desert of California. This specimen represents the first occurrence of the family Dorypygidae in the cratonic facies of the Lower Cambrian in the California-western Nevada region, as all of the few previous reports of the family (mostly Bonnia) have been from much thicker, more distal open-shelf deposits far to the northwest in the White-Inyo-Esmeralda County region of California and Nevada. Although still relatively rare, the occurrence of Dorypygidae across a range of environments biofacies realms in this area is typical of their distribution in other regions.
We applied tandem U-Pb dating of detrital zircon (DZ) to redefine the Tonto Group in the Grand Ca... more We applied tandem U-Pb dating of detrital zircon (DZ) to redefine the Tonto Group in the Grand Canyon region (Arizona, USA) and to modify the Cambrian time scale. Maximum depositional ages (MDAs) based upon youngest isotope-dilution DZ ages for the Tapeats Sandstone are ≤508.19 ± 0.39 Ma in eastern Grand Canyon, ≤507.68 ± 0.36 Ma in Nevada, and ≤506.64 ± 0.32 Ma in central Arizona. The Sixtymile Formation, locally conformable below the Tapeats Sandstone, has a similar MDA (≤508.6 ± 0.8 Ma) and is here added to the Tonto Group. We combined these precise MDAs with biostratigraphy of trilobite biozones in the Tonto Group. The Tapeats Sandstone is ca. 508–507 Ma; the Bright Angel Formation contains Olenellus, Glossopleura, and Ehmaniella biozones and is ca. 507–502 Ma; and the Muav Formation contains Bolaspidella and Cedaria biozones and is ca. 502–499 Ma. The Frenchman Mountain Dolostone is conformable above the Muav Formation and part of the same transgression; it replaces McKee’s Und...
ABSTRACT The first fossil hemipteran from the Late Jurassic of North America, Morrisonnepa jurass... more 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.
Trilobites appeared and diversified rapidly in the Cambrian, but it is debated as to whether thei... more Trilobites appeared and diversified rapidly in the Cambrian, but it is debated as to whether their radiations and extinctions were globally synchronous or geographically restricted and diachronous. The end of the early Cambrian is a classic example—it has traditionally been defined by the extinction of olenellid and redlichiid trilobites and the appearance of paradoxidid trilobites. Here we integrate the global biostratigraphy of these three trilobite groups with high-precision tuff and tandem detrital zircon U-Pb age constraints to falsify prior models for global synchronicity of these events. For the first time, we demonstrate that olenellid trilobites in Laurentia went extinct at least 3 Ma after the first appearance of paradoxidids in Avalonia and West Gondwana (ca. 509 Ma). They also disappeared before the extinction of redlichiids and prior to the base of the Miaolingian at ca. 506 Ma in South China. This indicates that these three trilobite groups (paradoxidids, olenellids, a...
The Little Houston Quarry in the Black Hills of Wyoming contains the most diverse vertebrate faun... more The Little Houston Quarry in the Black Hills of Wyoming contains the most diverse vertebrate fauna in the Morrison Formation (Upper Jurassic) north of Como Bluff and the second-most diverse in the entire formation, after Reed’s Quarry 9. The deposit was an occasionally reactivated abandoned river channel, in interbedded green mudstone and laminated green-gray siltstone above a channel sandstone. The dinosaur material is densely distributed and is disarticulated to articulated, with several associated skeletons. The biota contains charophytes, horsetails, a possible seed fern, possible conifers, gastropods, two types of unionoid bivalves, diplostracans (“conchostracans”), a malacostracan, ray-finned fish, lungfish, a frog, salamanders, two types of turtles, rhynchocephalians, a lizard, choristoderes, two types of crocodyliforms, a pterosaur, Allosaurus and several types of small theropods including Tanycolagreus? and probable dromaeosaurids, numerous Camarasaurus and a diplodocine sa...
In the summer of 1878, American paleontologist Edward Drinker Cope published the discovery of a s... more 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...
A left mandible of a small crocodyliform found in the Upper Jurassic Morrsion Formation of northe... more 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.
Redescription of a trackway from the Salt Wash Member of the Morrison Formation (Upper Jurassic) ... more 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.
The accuracy of the Content should not be relied upon and should be independently verified with p... more The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden.
More than 130 footprints representing ~43 trackways of birds (avian theropods) and two nonavian t... more More than 130 footprints representing ~43 trackways of birds (avian theropods) and two nonavian theropods occur as seven separate assemblages on loose blocks recovered from the Poison Strip Member of the Cedar Mountain Formation, near the Stikes Quarry locality in eastern Utah. Six of assemblages, four with bird tracks and two with small non avian theropod tracks, are inferred to originate from the same stratigraphic horizon, and can therefore be considered part of the same ichnofauna. The seventh assemblages comes from a different horizon a few meters above that yielding the other six assemblages. The bird tracks are all attributed to the ichnogenus Aquatilavipes, a track type morphologically similar to those of modern shorebirds. The ichnogenus is also known from broadly coeval ichnofaunas from South Dakota and Canada, and
We describe a microvertebrate assemblage from the J&M site, of the Upper Cretaceous (Campanian-Ma... more We describe a microvertebrate assemblage from the J&M site, of the Upper Cretaceous (Campanian-Maastrichtian) Williams Fork Formation. Breakdown of fossil bearing matrix was achieved with the use of heated dimethyl sulfoxide. Nine of the recovered taxa are new to both the J&M site and the Williams Fork Formation. The sharks Lonchidion griffisi, Chiloscyllium sp., and Cantioscyllium markaguntensis are the first non-batoid elasmobranchs reported from the Williams Fork Formation and are all represented by teeth. The rays Cristomylus and Psuedomyledaphus are also newly reported from teeth. The most common identifiable fossils were teeth of indeterminate amiids, most likely belonging to Melvius. Osteichthyan fossils new to the Williams Fork Formation include teeth of Paralbula, an indeterminate pycnodontid tooth plate fragment, and an indeterminate lungfish tooth fragment. A tooth of the teiid Peneteius is also the first reported from within the Williams Fork Formation. Alligatoroid teeth are relatively common and are extremely similar to those of the contemporaneous durophage Brachychampsa but are generically indeterminate. Terrestrial taxa were recovered in much smaller numbers. Theropod dinosaur fossils included isolated tooth fragments belonging to an indeterminate dromaeosaurid and, possibly, to Richardoestesia. We recovered both multituberculate and metatherian fossils in the form of isolated teeth. Some of these taxa are known from marine and estuarine deposits and, given that so many of these marine associated taxa have been recovered together, it seems likely that the J&M site is recording marine or estuarine influence within at least part of its depositional history. The mammalian taxa suggest a Judithian-Lancian age for the site, while records of the squamate Peneteius and the ray Myledaphus, suggest that the J&M site may be temporally transitional between other late Campanian and late Maastrichtian-aged localities.
The Morrison Formation contains a number of large quarries that have yielded dinosaurs and other ... more The Morrison Formation contains a number of large quarries that have yielded dinosaurs and other vertebrates, and many of these occur in sandstone beds representing ancient river channels. However, a number of very productive sites occur in mudstone beds representing other environments such as ephemeral ponds, and some of these yield both large dinosaurs and microvertebrates; these localities in mudstone beds represent different taphonomic modes of preservation and often preserve vertebrate taxa in different relative abundances from the channel sandstone sites. Among these important and very productive mudstone localities are the Cleveland-Lloyd Quarry, the Mygatt-Moore Quarry, and the microvertebrate sites of the Fruita Paleontological Area, and each of these preserves distinct vertebrate paleofaunas, different from sandstone sites and from each other, suggesting that mudstone localities had a very different mode of sampling the local biotas than did sites in sandstone.
New data related to the definition of the Oxfordian/Kimmeridgian boundary obtained mostly after 2... more New data related to the definition of the Oxfordian/Kimmeridgian boundary obtained mostly after 2006 are discussedi.e. after the proposal for the uniform boundary of the stages at the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland has been given. This boundary is based on the Subboreal-Boreal ammonite successions-where it is distinguished at the base of the Subboreal Baylei Zone which is defined by the Pictonia flodigarriensis horizon, and which corresponds strictly to the base of the Boreal Bauhini Zone. This boundary is defined also by other stratigraphical data-both palaeontological, geochemical and palaeomagnetical (including its well defined position close to the boundary between magnetozones F3n, and F3r-the latter corresponding to marine magnetic anomaly M26r). The boundary and the section are thus proposed as the GSSP for the Oxfordian/Kimmeridgian boundary. The boundary is well recognizable also in other sections of Subboreal and Boreal areas as discussed in the study, including southern England,
Vertebrate tracks are comparatively rare in Tertiary deposits of the western United States. Unlik... more Vertebrate tracks are comparatively rare in Tertiary deposits of the western United States. Unlike the deposits of the Mesozoic in this region, in which each formation often has several dozen known tracksites, there are only a few known sites in Paleocene units of the region (Lockley and Hunt, 1995), and though the Eocene Green River Formation contains relatively numerous tracks, especially those of birds, there are only a few taxa represented. The occurrence of amphibian tracks in the Eocene Wasatch Formation is therefore of interest, not only in that it adds to the known ichnological record of the Tertiary of the western United States but also in that the tracks indicate the presence of an otherwise under-represented member of the vertebrate paleofauna of the time. Skeletal remains of amphibians are present but not common in many Tertiary formations of the western United States, and remains of large salamanders are rare. Only the large caudate Piceoerpeton is known from the Tiffanian and Clarkforkian of Montana and Wyoming (Naylor and Krause, 1981), and its only Wasatchian occurrence is at Ellesmere Island, north of the Arctic Circle. The tracks described here appear to represent a nearly Piceoerpeton-sized salamander in the lacustrine shoreline deposits of the early Eocene Wasatch Formation of southwestern Wyoming.
... However, Batrachopus foot-prints might be confused with synapsid footprints in some cases (Sc... more ... However, Batrachopus foot-prints might be confused with synapsid footprints in some cases (Schultz-Pittman ... mammal prints and are thought to have been made by a mammal-like reptile (?therapsid)). ... structures found in GS-ENM are not as well preserved as tracks from some ...
The famous bone beds of the Morrison Formation, whose rocks are exposed from Wyoming down through... more The famous bone beds of the Morrison Formation, whose rocks are exposed from Wyoming down through the red rock region of the American Southwest, have yielded one of the most complete pictures of any ancient vertebrate ecosystem in the world. After more than a century of exploration, the Morrison continues to yield new discoveries about a time so different from our own that it almost seems imaginary. Aimed at the general reader, Jurassic West tells the story of the life of this ancient world as scientists have so far been able to reconstruct it. The book recounts the discovery of many important Late Jurassic dinosaurs such as Apatosaurus, Allosaurus, and Stegosaurus. But dinosaurs comprise barely a third of the more than 90 types of vertebrates known from the Formation, which include crocodiles and turtles, frogs and salamanders, dinosaurs and mammals, clams and snails, and ginkgoes, ferns, and conifers.
... collected from there by Museum of Geology crews in 1980 and again in 199 1. Most of the mater... more ... collected from there by Museum of Geology crews in 1980 and again in 199 1. Most of the material comes from the middle of the Morrison undifferentiated and ... The fos-sil-bearing layer is approximately 1 meter thick and occurs immediately above a thin, lenticular sandstone unit ...
The Mygatt-Moore Quarry is a deposit of several thousand dinosaur bones in the Brushy Basin Membe... more 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 more than 30 years and nearly 2400 mapped specimens have been collected. This study gathered data about the quarry from many sources to investigate the origin of the deposit. The Mygatt-Moore Quarry appears to be an attritional deposit of a relatively restricted diversity of dinosaurs, with few other non-dinosaurian taxa, that accumulated in a vernal pool deposit in an overbank setting. Bone modification was mostly by corrosion and breakage by trampling; scavenging was abundant. The paleofauna is dominated by Allosaurus and Apatosaurus (MNI and NIS), with the polacanthid ankylosaur Mymoorapelta less common. The matrix of the main quarry layer includes abundant carbonized fragments of plant material, and the mud during the time of deposition may have been often at least damp and occasionally acidic and dysoxic. ...
The Upper Jurassic Morrison Formation of western North America has yielded a number of specimens ... more 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 ...
A trilobite pygidium, likely referable to the genus Bonnima, is the first evidence of a member of... more A trilobite pygidium, likely referable to the genus Bonnima, is the first evidence of a member of the Corynexochida reported from the Lower Cambrian (Dyeran Stage) Chambless Limestone of the southern Marble Mountains in the Mojave Desert of California. This specimen represents the first occurrence of the family Dorypygidae in the cratonic facies of the Lower Cambrian in the California-western Nevada region, as all of the few previous reports of the family (mostly Bonnia) have been from much thicker, more distal open-shelf deposits far to the northwest in the White-Inyo-Esmeralda County region of California and Nevada. Although still relatively rare, the occurrence of Dorypygidae across a range of environments biofacies realms in this area is typical of their distribution in other regions.
We applied tandem U-Pb dating of detrital zircon (DZ) to redefine the Tonto Group in the Grand Ca... more We applied tandem U-Pb dating of detrital zircon (DZ) to redefine the Tonto Group in the Grand Canyon region (Arizona, USA) and to modify the Cambrian time scale. Maximum depositional ages (MDAs) based upon youngest isotope-dilution DZ ages for the Tapeats Sandstone are ≤508.19 ± 0.39 Ma in eastern Grand Canyon, ≤507.68 ± 0.36 Ma in Nevada, and ≤506.64 ± 0.32 Ma in central Arizona. The Sixtymile Formation, locally conformable below the Tapeats Sandstone, has a similar MDA (≤508.6 ± 0.8 Ma) and is here added to the Tonto Group. We combined these precise MDAs with biostratigraphy of trilobite biozones in the Tonto Group. The Tapeats Sandstone is ca. 508–507 Ma; the Bright Angel Formation contains Olenellus, Glossopleura, and Ehmaniella biozones and is ca. 507–502 Ma; and the Muav Formation contains Bolaspidella and Cedaria biozones and is ca. 502–499 Ma. The Frenchman Mountain Dolostone is conformable above the Muav Formation and part of the same transgression; it replaces McKee’s Und...
ABSTRACT The first fossil hemipteran from the Late Jurassic of North America, Morrisonnepa jurass... more 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.
Trilobites appeared and diversified rapidly in the Cambrian, but it is debated as to whether thei... more Trilobites appeared and diversified rapidly in the Cambrian, but it is debated as to whether their radiations and extinctions were globally synchronous or geographically restricted and diachronous. The end of the early Cambrian is a classic example—it has traditionally been defined by the extinction of olenellid and redlichiid trilobites and the appearance of paradoxidid trilobites. Here we integrate the global biostratigraphy of these three trilobite groups with high-precision tuff and tandem detrital zircon U-Pb age constraints to falsify prior models for global synchronicity of these events. For the first time, we demonstrate that olenellid trilobites in Laurentia went extinct at least 3 Ma after the first appearance of paradoxidids in Avalonia and West Gondwana (ca. 509 Ma). They also disappeared before the extinction of redlichiids and prior to the base of the Miaolingian at ca. 506 Ma in South China. This indicates that these three trilobite groups (paradoxidids, olenellids, a...
The Little Houston Quarry in the Black Hills of Wyoming contains the most diverse vertebrate faun... more The Little Houston Quarry in the Black Hills of Wyoming contains the most diverse vertebrate fauna in the Morrison Formation (Upper Jurassic) north of Como Bluff and the second-most diverse in the entire formation, after Reed’s Quarry 9. The deposit was an occasionally reactivated abandoned river channel, in interbedded green mudstone and laminated green-gray siltstone above a channel sandstone. The dinosaur material is densely distributed and is disarticulated to articulated, with several associated skeletons. The biota contains charophytes, horsetails, a possible seed fern, possible conifers, gastropods, two types of unionoid bivalves, diplostracans (“conchostracans”), a malacostracan, ray-finned fish, lungfish, a frog, salamanders, two types of turtles, rhynchocephalians, a lizard, choristoderes, two types of crocodyliforms, a pterosaur, Allosaurus and several types of small theropods including Tanycolagreus? and probable dromaeosaurids, numerous Camarasaurus and a diplodocine sa...
In the summer of 1878, American paleontologist Edward Drinker Cope published the discovery of a s... more 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...
A left mandible of a small crocodyliform found in the Upper Jurassic Morrsion Formation of northe... more 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.
Redescription of a trackway from the Salt Wash Member of the Morrison Formation (Upper Jurassic) ... more 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.
The accuracy of the Content should not be relied upon and should be independently verified with p... more The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden.
More than 130 footprints representing ~43 trackways of birds (avian theropods) and two nonavian t... more More than 130 footprints representing ~43 trackways of birds (avian theropods) and two nonavian theropods occur as seven separate assemblages on loose blocks recovered from the Poison Strip Member of the Cedar Mountain Formation, near the Stikes Quarry locality in eastern Utah. Six of assemblages, four with bird tracks and two with small non avian theropod tracks, are inferred to originate from the same stratigraphic horizon, and can therefore be considered part of the same ichnofauna. The seventh assemblages comes from a different horizon a few meters above that yielding the other six assemblages. The bird tracks are all attributed to the ichnogenus Aquatilavipes, a track type morphologically similar to those of modern shorebirds. The ichnogenus is also known from broadly coeval ichnofaunas from South Dakota and Canada, and
Uploads
Papers by John Foster