Julia B McHugh

Two tooth-bearing snout fragments from a diplodocid sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic) excavated from the Mygatt-Moore Quarry in Rabbit Valley, Colorado are described. The Mygatt-Moore Quarry has produced thousands of vertebrate fossils from the Brushy Basin Member, with the diplodocid Apatosaurus cf. louisae and the tetanuran Allosaurus fragilis dominating the assemblage. Additionally, remains of another diplodocid, Diplodocus sp., have been found near the quarry within Rabbit Valley. Both specimens in this study preserve eight teeth per alveolar position, as observed through broken surfaces at the gross anatomical level and also through computed tomography (CT) scans. This is inconsistent with the genus Diplodocus sp., which has been previously shown to have a maximum of six teeth per alveolus. The presence of eight replacement teeth per alveolus has previously only been reported in the Cretaceous rebbachisaurid Nigersaurus taqueti, which has been interpreted to have occupied a similar ground-height browsing feeding strategy to both Diplodocus and Apatosaurus. This is the first report of this type of high-count replacement teeth in a diplodocid sauropod from the Morrison Formation. The high number of replacement teeth in a close relative to the contemporaneous Diplodocus provides evidence for niche partitioning among the contemporary ground-height browsing diplodocid sauropods of the Late Jurassic Period in North America.

Field work protocols in the recovery of vertebrate fossils can vary between sites, and also within sites, due to differing researcher goals. Disparate researcher priorities can affect the resulting collections in terms of species richness, size distribution, specimen completeness, taphonomic condition, and aesthetic value. We examined paleoecological data, in the form of bone surface modifications (e.g., abrasion, feeding traces, etc.), from a single site worked by multiple collectors to determine the sensitivity of this type of data to collector bias. We examined 2,368 fossils from the Mygatt-Moore Quarry and divided them into two cohorts: 2016–2019 (bulk collection under a single collector) and pre-2016 (mixed collectors and priorities). Frequencies of modified bone surfaces were then calculated in each cohort among the recovered specimens. However, the specimens within the cohorts were of unequal size, completeness, and amount of preserved surface area, making inferences of modif...

<div><p>ABSTRACT</p><p>Temnospondyl amphibians are a large and diverse group of early tetrapods, whose paleohistology has been incompletely studied. Here, humeri of <i>Micropholis stowi</i> and <i>Lydekkerina huxleyi</i> from the Karoo Basin of South Africa (Katberg Formation) were thin–sectioned for paleohistological analysis. Diaphyseal bone histology of both taxa exhibits a convergence to fibrolamellar tissue and an absence of lines of arrested growth; additionally, medullary cavities free of trabeculae support terrestrial lifestyles in both <i>Micropholis</i> and <i>Lydekkerina</i>. The presence of azonal tissue in <i>Micropholis</i> is unlike that of other dissorophoids or extant caudatans, suggesting an adaptation to local conditions in the Early Triassic of the Karoo Basin, as well as a complicated and incompletely studied pattern of histological evolution in dissorophoids. Additionally, the propodial histology of these and 12 other taxa were assessed through different broad–scale phylogenetic hypotheses for Temnospondyli. Results reveal convergence towards sustained, non–cyclical growth and an absence of lines of arrested growth in the diaphyses of Early Triassic temnospondyls. The optimization of histological traits on to existing phylogenetic hypotheses is equally parsimonious between the different topologies. Homoplasy among histological characters suggests that evolutionary history in this group is overshadowed by developmental plasticity in bone microstructure, potentially due to environmental and biomechanical constraints. However, the interpretation of these data is limited by small sample size, and increased sampling is required to validate the patterns revealed in this study.</p><p>http://zoobank.org/urn:lsid:zoobank.org:pub:7CF4CD42–3C8B–43F3–83A1–7C611C5CDBB8</p><p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="http://www.tandfonline.com/UJVP" target="_blank">www.tandfonline.com/UJVP</a></p></div

Two tooth-bearing snout fragments from a diplodocid sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic) excavated from the Mygatt-Moore Quarry in Rabbit Valley, Colora­do are described. The Mygatt-Moore Quarry has produced thousands of vertebrate fossils from the Brushy Basin Member, with the diplodocid Apatosaurus cf. louisae and the tetanuran Allosaurus fragilis dominat­ing the assemblage. Additionally, remains of another diplodocid, Diplodocus sp., have been found near the quarry within Rabbit Valley. Both specimens in this study preserve eight teeth per alveolar position, as observed through broken surfaces at the gross anatomical level and also through computed tomography (CT) scans. This is inconsistent with the genus Diplodocus sp., which has been previously shown to have a maximum of six teeth per alveolus. The presence of eight replacement teeth per alveolus has previously only been reported in the Cretaceous rebbachisaurid Nigersaurus taqueti, ...

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 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.

ABSTRACT Temnospondyl amphibians are a large and diverse group of early tetrapods, whose paleohistology has been incompletely studied. Here, humeri of Micropholis stowi and Lydekkerina huxleyi from the Karoo Basin of South Africa (Katberg Formation) were thin-sectioned for paleohistological analysis. Diaphyseal bone histology of both taxa exhibits a convergence to fibrolamellar tissue and an absence of lines of arrested growth; additionally, medullary cavities free of trabeculae support terrestrial lifestyles in both Micropholis and Lydekkerina. The presence of azonal tissue in Micropholis is unlike that of other dissorophoids or extant caudatans, suggesting an adaptation to local conditions in the Early Triassic of the Karoo Basin, as well as a complicated and incompletely studied pattern of histological evolution in dissorophoids. Additionally, the propodial histology of these and 12 other taxa were assessed through different broad-scale phylogenetic hypotheses for Temnospondyli. Results reveal convergence towards sustained, non-cyclical growth and an absence of lines of arrested growth in the diaphyses of Early Triassic temnospondyls. The optimization of histological traits on to existing phylogenetic hypotheses is equally parsimonious between the different topologies. Homoplasy among histological characters suggests that evolutionary history in this group is overshadowed by developmental plasticity in bone microstructure, potentially due to environmental and biomechanical constraints. However, the interpretation of these data is limited by small sample size, and increased sampling is required to validate the patterns revealed in this study.

ABSTRACT Rhinesuchids are a basal group of stereospondyls, one of the most successful groups of early amphibians. They are also the only group of stereospondyl amphibians present prior to the Permian—Triassic boundary. Here, Rhinesuchus postcranial material is sampled for paleohistological analysis for the first time and gives us a model for growth in basal stereospondyls. Bone microstructure confirms an aquatic lifestyle for Rhinesuchus, and indicates that it was a long-lived taxon (>30 years), growing seasonally like other amphibians. The shaft of the iliac dorsal process preserves the largest number of rest lines, suggesting it as a preferred element to estimate minimum age in basal stereospondyls. Femoral diaphyseal sections are readily comparable to distal rib sections for skeletochronological purposes, but preserve fewer rest lines than the ilium. Narrowly banded annuli and rest lines in the inner cortex of Late Permian elements indicate a taxon that was able to weather successive seasons of harsh conditions, and perhaps indicates a reason for the success of Stereopsondyli through the Permo-Triassic mass extinction.

A survey of 2,368 vertebrate fossils from the Upper Jurassic Mygatt-Moore Quarry (MMQ) (Morrison Formation, Brushy Basin Member) in western Colorado revealed 2,161 bone surface modifications on 884 specimens. This is the largest, site-wide bone surface modification survey of any Jurassic locality. Traces made by invertebrate actors were common in the assemblage, second in observed frequency after vertebrate bite marks. Invertebrate traces are found on 16.174% of the total surveyed material and comprise 20.148% of all identified traces. Six distinct invertebrate trace types were identified, including pits and furrows, rosettes, two types of bioglyph scrapes, bore holes and chambers. A minimum of four trace makers are indicated by the types, sizes and morphologies of the traces. Potential trace makers are inferred to be dermestid or clerid beetles, gastropods, an unknown necrophagous insect, and an unknown osteophagus insect. Of these, only gastropods are preserved at the site as body...

Temnospondyl amphibians are a large and diverse group of early tetrapods, whose paleohistology has been incompletely studied. Here, humeri of Micropholis stowi and Lydekkerina huxleyi from the Karoo Basin of South Africa (Katberg Formation) were thin-sectioned for paleohistological analysis. Diaphyseal bone histology of both taxa exhibits a convergence to fibrolamellar tissue and an absence of lines of arrested growth; additionally, medullary cavities free of
trabeculae support terrestrial lifestyles in both Micropholis and Lydekkerina. The presence of azonal tissue in Micropholis is unlike that of other dissorophoids or extant caudatans, suggesting an adaptation to local conditions in the Early Triassic of the Karoo Basin, as well as a complicated and incompletely studied pattern of histological evolution in dissorophoids. Additionally, the propodial histology of these and 12 other taxa were assessed through different broad-scale phylogenetic hypotheses for Temnospondyli. Results reveal convergence towards sustained, non-cyclical growth and an absence of lines of arrested growth in the diaphyses of Early Triassic temnospondyls. The optimization of histological traits on to existing phylogenetic hypotheses is equally parsimonious between the different topologies. Homoplasy among histological characters suggests that evolutionary history in this group is overshadowed by  evelopmental plasticity in bone microstructure, potentially due to environmental and biomechanical constraints. However, the interpretation of these data is limited by small
sample size, and increased sampling is required to validate the patterns revealed in this study.

The biostratigraphy of the Eocene and Oligocene Renova Formation (Duchesnean and Chadronian, Bozeman Group) at McCarty's Mountain and Mantle Ranch, Beaverhead Basin, southwestern Montana was surveyed to determine the structure and changes of ...