|NPS Paleontology Research Abstract Volume|
Although Dinosaur National Monument is most famous for the dinosaur bones that are found within its boundaries, it also contains several localities that contain plant megafossils. These fossils are found in the Morrison Formation of late Jurassic age and for the most part have not yet been studied. The Morrison plant fossils are preserved as compressions, impressions, and petrifications. Unfortunately, the leaf compressions are, for the most part, highly fragmented and unidentifiable. Some, however, are large enough to identify at least to the generic level and show that ferns, conifers, and other groups are present. A manuscript has been submitted for publication that records the presence of the unusual leaf Czekanowskia at one of these localities in the monument. This discovery is significant because the fossil is considered to be indicative of a humid climate and its occurrence in the monument suggests that the Morrison was deposited under similar climatic conditions.
Two Jurassic dinosaur quarries occur in the state of Utah -- the Cleveland-Lloyd Dinosaur Quarry, a National Landmark, and Dinosaur National Monument. The dinosaur fossils in both quarries occur in the Brushy Basin Member of the Morrison Formation, well below the boundary with the Lower Cretaceous Cedar Mountain Formation. Due to similarities in the dinosaur faunas and in the rocks of the enclosing formations, the fossiliferous strata in the quarries generally are considered nearly contemporaneous. Analyses of biotites from volcaniclastic, montmorillonitic claystone collected in proximity to the quarries reveal disparate dates, 146.8 +1 Ma for a claystone 1.5 m above the fossiliferous interval at the Cleveland-Lloyd Dinosaur Quarry, and 135.2 +5.5 Ma for a claystone 11 m above the main fossiliferous interval at Dinosaur National Monument. Therefore the quarry at Dinosaur National Monument is substantially younger than the one at the Cleveland-Lloyd Dinosaur Quarry and much of the uppermost Brushy Basin at Dinosaur NM is Early Cretaceous rather than Late Jurassic.
Petrologic analyses of the Middle Jurassic through Lower Cretaceous rocks at the Cleveland-Lloyd Dinosaur Quarry reveal a regressive sequence from the intertidal beds of the Summerville, through the supratidal deposits of the Tidwell Member of the Morrison, into the continental deposits of the rest of the Morrison and Cedar Mountain formations. At Dinosaur National Monument the transition from the marine Sundance Formation to the fluvial Morrison Formation was rapid. Source areas for the two localities were similar, although pulses of cherty conglomerate from the west occur more frequently and earlier at Dinosaur NM. The clay mineral suites are similar, revealing syngenetic neoformations indicative of the paleoclimates. Particularly at the Cleveland-Lloyd Dinosaur Quarry there appears to be a progression from arid to monsoonal to humid conditions, which coincidentally helps define the formation and member boundaries. The paraconformity the encompasses much of the Berriasian at the Cleveland-Lloyd and the caliche, magadiite-type chert, and dolomite in the uppermost Brushy Basin at Dinosaur NM attest to an arid environment, coinciding with uplift to the west during the early pulses of the Sevier orogeny.
Two new specimens of the rare carnivorous dinosaur Marshosaurus have been collected from in and near Dinosaur National Monument, including the first cranial material of this species. The skull of Marshosaurus is primitive in having an unconstricted lateral temporal fenestra but derived in possessing a system of pneumatic fenestra in the braincase similar to the pattern seen in tyrannosaurids. Preliminary phylogenetic analysis indicates that Marshosaurus is a carnosaurian tetanuran. The articulated vertebral columns will allow for identification of isolated Marshosaurus bones from the type locality, the Cleveland-Lloyd Quarry.
The new specimens extend the geographic distribution of this taxon into NE Utah and NW Colorado. They also extend the range from high in the Brushy Basin Member (early Tithonian) to far down into the Salt Wash Member (late Kimmeridgian). The associated fauna includes crocodilians, turtles, and Stegosaurus and indicates that typical Brushy Basin fauna probably arose during Salt Wash times.
A NEW CARNOSAURIAN DINOSAUR (SAURISCHIA: TETANURAE) FROM THE
SALT WASH MEMBER OF THE MORRISON FORMATION (JURASSIC:KIMMERIDGIAN) OF DINOSAUR NATIONAL MONUMENT
Dinosaur National Monument
A small partial skeleton of an ornithopod dinosaur was collected from bentonitic mudstone in the upper part (Tithonian) of the Brushy Basin Member of the Morrison Formation. The specimen consists of two posterior cervical and six anterior dorsal vertebrae, five anterior caudal vertebrae, scapula, coracoid, humerus, tibia, fibula, and dorsal ribs. On the basis of distinctively shaped coracoid the specimen is referred to Camptosaurus, a common Morrison ornithopod which reached lengths of 8 meters. Bone texture, extreme small size, and some morphological features indicates that the specimen is the remains of an advanced embryo, even though there is no associated eggshell. The unossified epiphyses of the long bones suggests that Camptosaurus hatchlings were altricial. Estimated total length is 240 mm.
Beds at or near the fossil horizon are characterized by smectitic overbank and lacustrine mudstones with scattered isolated fluvial channel sandstones. The locality is 10 m stratigraphically above the level of the famous Carnegie Dinosaur Quarry. Both the Dinosaur specimen and embryonic and hatchling Dryosaurus specimens from western Colorado are located in alluvial plain sediments of the Morrison Formation some 200-300 km downstream from inferred highland sediment source areas to the west.
(in press) "Dinosaur eggs & babies", Cambridge University Press
This proposal seeks permission to conduct a detailed study of Jurassic-Cretaceous nonmarine sedimentary rocks within the boundaries of Dinosaur National Monument. These rocks, known as the Morrison, Cedar Mountain, and Dakota Formations, record the initial development of the Cordilleran foreland basin during the late Jurassic and early Cretaceous time. However, due to variable facies relationships and internal stratigraphic complexity, correlation between depositional systems and foreland basin development is enigmatic. In order to better understand basin evolution, the primary goals of this study are to: 1) reconstruct basin architecture and depositional systems of the Morrison, Cedar Mountain and Dakota Formations; 2) determine sediment provenance; 3) define a chrono-stratigraphic framework for nonmarine deposition; and 4) develop a sequence stratigraphic approach to interpreting nonmarine facies evolution within the Cordilleran foreland basin. The detailed stratigraphic resolution generated by this study will facilitate the identification of important surfaces of discontinuity and define regional depositional packages. The sedimentologic nature of these packages, as well as their three-dimensional distribution, will offer insight into the tectonic, eustatic, and climatic factors affecting early Cordilleran foreland basin evolution.
A microvertebrate locality in the Rainbow Park area of Dinosaur National Monument has yielded a diverse fauna of small vertebrates, including mammals. Specimens have been recovered from two quarries by hand quarrying and screenwashing of quarried matrix. Both quarries are within the Brushy Basin Member of the Morrison Formation and are stratigraphically and geographically close to each other. Both occur in mudstones but probably represent somewhat different overbank facies. The mammalian element of the fauna is represented primarily by more than 100 isolated teeth and includes: a triconodont, at least two species of multituberculates, a symmetrodont at least two species of dryolestids, and a paurodontid. No docodonts have been identified yet. One specimen is a partial skull of a multituberculate that preserves a complete palate with upper dentition.
49th SVP Meeting, Austin, Texas, 1989.
One of the most vexing problems facing dinosaur ichnology is making an accurate identification of a trackmaker. Using dinosaur footprints to make ichnological censuses for comparison with skeletal faunas, to investigate the extent to which ichnofacies correspond to lithological facies, or to make interpretations of the behavior of trackmakers, depends in large degree on whether tracks can be correctly ascribed to their makers. For tridactyl footprints of bipedal dinosaurs, such assignments have hitherto been based largely on the gross appearance of tracks, their "gestalt". Attempts have been made to use multivariate statistical techniques to discriminate theropod tracks from ornithopod prints, but in the absence of independent criteria for assigning footprints to zoological taxa in the first place, such approaches seem to be little more than extended exercises in circular reasoning.
I have sought criteria by which footprint taxa might better be correlated with skeletal taxa of dinosaurs. My approach is to examine the foot skeletons of described dinosaur taxa for features that might be expected to be preserved in tracks made by these animals, and then to see if different groups of potential makers of tridactyl tracks differ in any of these features. A critical assumption here, of course, is that the fleshy features of a bipedal dinosaur's foot closely matched its underlying bony structure. This assumption will probably not always be warranted. However, my observations on the feet of ground-living birds lead me to believe that the assumption is more nearly valid than not.
During the next year I will use the criteria developed in this report to make tentative identifications of the kinds of dinosaurs responsible for footprint taxa (Eubrontes, Gigandipus, Anchisauripus, Grallator, Anomoepus, etc.) of the classic Connecticut ichnofauna. Preliminary comparisons suggest that the traditional identifications of Anchisauripus and Eubrontes tracks as those of tetrapods are correct.
A small slab from the Brushy Basin Member of the Morrison Formation in Dinosaur National Monument contains the first articulated frogs from the Upper Jurassic of North America. The remains of nearly a dozen individuals are preserved. The specimens are small, measuring less than 1 inch in total length. The degree of ossification, the lack of well formed ends to the humerus and femur, and the unfused neural arches in the vertebral column indicate that these frogs were metamorphosing when they died. Identification of these individuals has not yet been completed but they may represent a previously unknown species of frog. Other frog species from the site include Comobatrachus and Eobatrachus, frogs previously reported only from a locality in the Morrison of Wyoming.
Evidently special circumstances were necessary to silicify and thus preserve the dinosaur and other reptile bones at Dinosaur National Monument (DNM). Not only are the bones silicified, but the enclosing sandstone is also cemented by silica. The other sandstones at DNM and elsewhere in the Brushy Basin Member seem to be largely cemented by calcite and generally lack reptile bones.
I propose to cut thin sections of selected dinosaur bones, particularly those with canals, in order to observe the patterns of silicification. Perhaps some 20 samples of bone will be needed to obtain a representative selection of the three bone horizons and different types of dinosaurs. Also, as needed, scanning electron microscope images will be made of bones, using fingernail size pieces of bone. Thin sections will also be cut from several samples of sandstone matrix of each bone horizon to see if the diagenetic mineral sequence in the sandstone horizons matches or contrasts with that of the bones.
It may be possible to determine if the bones were silicified in one stage or whether there was more than one stage, for example an early burial stage where silt was incorporated within the earliest cement layer in the canals, followed by silt-free cement layers. Furthermore, if some of the bones have contrasting cement stratigraphies, for example calcite-, silica-, or hematite-dominated, then perhaps it would be possible to determine if some of the bones had been hardened elsewhere before being transported to their final resting place, as has proved possible with dinosaur bones of Late Cretaceous age in southern Alberta.
During Late Jurassic time, a shallow braided river with a gravel-sand bedload deposited the fluvial strata of the Salt Wash Member of the Morrison Formation in Dinosaur National Monument. An articulated Allosaurus skeleton is being excavated at the Monument from the upper portion of a 60 cm layer of conglomerate at the bottom of a paleochannel 1.4 m deep. A high-energy flood cut the channel into a coset of planar crossbed sets built by coalescing transverse bars, probably of linguoid shape. The flood waters transported and deposited the gravel and the Allosaurus carcass. As the flood stage fell, the carcass was rapidly buried, mostly by down channel migration of trains of three-dimensional dunes of the lower flow regime that deposited a coset of trough crossbedded sands. Simultaneously, the carcass was partly covered by plane-bedded sand deposited in the upper flow regime, the lateral transition from dunes being caused by slightly higher velocities in that part of the channel. The skeleton was preserved due to its location in a topographic low and rapid burial, which protected it from scavengers and exhumation by subsequent floods.
Utah Geological Survey, Miscellaneous Publication 92-3, 1992.
Recent studies indicate that the older Mesozoic sedimentary rocks of the Dinosaur National Monument area are rich in vertebrate tracksites. A total of 21 tracksites have been discovered in the Late Triassic Popo Agie/Chinle Formation in the last few years. Three tracksites have also been discovered in the lower part of the Glen Canyon Group. The Popo Agie/Chinle sites are particularly significant because they yield the trackways of most of the major groups of reptiles known from this epoch (dinosaurs, mammal-like reptiles, phytosaurs, aetosaurs, lepidosaurs, ?trilophosaurs and tanystropheids). In fact the diversity of tracks rival the diversity of Late Triassic body fossils known from many sites in the well-known Chinle Formation, for example at the Petrified Forest National Park, and in the fossiliferous Dockum Group.
The discovery of aetosaur tracks (Brachychirotherium) in the lower part of Glen Canyon Group provides strong evidence for a Late Triassic age for the track-bearing bed. This is a significant contribution to unresolved questions about the age of the Glen Canyon Group in this area.
Utah Geological Survey, Miscellaneous Publications 92-3, 1992.
Although the Morrison Formation is well known for its abundance of large sauropod dinosaurs, juveniles from this formation are rare, and associated remains of juveniles are extremely rare. Although a few associated remains of juveniles have been described, additional undescribed specimens exist in the collections of Dinosaur National Monument.
This paper will 1) describe the morphology of juvenile specimens of Diplodocus from DNM, 2) compare the morphology of juvenile and adult Diplodocus, 3) test the constancy of the robustness ratio for long bones and constancy of the relative lengths of long bones in Diplodocus specimens of widely different ages, and 4) test the hypothesis that the robustness ratio and relative length of long bones are unique and ontogenetically constant for the common genera of Morrison sauropods. Confirmation of 3 and 4 would allow for the generic identification of isolated sauropod limb bones in the Morrison Formation.
The early Mesozoic records of salamanders is very poor and fragmentary. Pond deposits in the Brushy Basin Member of Dinosaur National Monument provide important evidence on the early evolution and diversification of these amphibians. Analysis of the material is currently underway, but at least two new species and one new genus have been recognized. An isolated atlantes shows features diagnostic for the family Karaururidae and would constitute the first occurrence of this salamander family in the western hemisphere. This study will examine the diversity and biogeography of Upper Jurassic salamanders.
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|United States Department of the Interior, National Park Service|