A5082932015- Paleontology and Evolutionary Biology
- Evolution and Paleontology Studies
- Ichthyology and Marine Biology
- Amphibian and Reptile Biology
- Wildlife Ecology and Conservation
- Morphological variations and asymmetry
- Avian ecology and behavior
- Paleontology and Stratigraphy of Fossils
- Turtle Biology and Conservation
- Optical measurement and interference techniques
- Geology and Paleoclimatology Research
- Botany, Ecology, and Taxonomy Studies
- Bone Tumor Diagnosis and Treatments
- Comparative Animal Anatomy Studies
- Geological and Geochemical Analysis
- Animal Behavior and Reproduction
- Animal Ecology and Behavior Studies
- Geological Studies and Exploration
- Plant Diversity and Evolution
- Ecology and Vegetation Dynamics Studies
- Developmental and Educational Neuropsychology
- Phagocytosis and Immune Regulation
- Education Discipline and Inequality
- Periodontal Regeneration and Treatments
- Shape Memory Alloy Transformations
Chapman University
2017-2024
Museum of the Rockies
2008-2020
Montana State University
2008-2020
Burke Museum of Natural History and Culture
2018
University of Washington
2018
Stanford University
2015-2016
University of California, Berkeley
2015-2016
University of Minnesota System
2015-2016
Museum für Naturkunde
2015-2016
GNS Science
2015-2016
ABSTRACT Ontogenetic changes in the bone histology of Maiasaura peeblesorum are revealed by six relatively distinct but gradational growth stages: early and late nestling, juvenile, sub-adult, adult. These stages distinguished not only relative size histological patterns bones at each stage. In general, earliest marked spongy matrix with large vascular canals. Through growth, cortical differentiates into fibro-lamellar tissue that tends to become more regularly layered outer cortex. By...
Twelve different bones from the skeleton of holotype specimen hadrosaurian dinosaur Hypacrosaurus stebingeri were thin-sectioned to evaluate significance lines arrested growth (LAGs) in age assessments. The presence an external fundamental system (EFS) at surface cortex and mature epiphyses indicate that had reached adulthood slowed considerably earlier stages. number LAGs varied none pedal phalanx as many eight tibia femur. Most elements experienced considerable Haversian reconstruction...
We performed multiple analyses of Tyrannosaurus rex (specimen MOR 1125) fibrous cortical and medullary tissues remaining after demineralization. The results indicate that collagen I, the main organic component bone, has been preserved in low concentrations these tissues. findings were independently confirmed by mass spectrometry. propose a possible chemical pathway may contribute to this preservation. presence endogenous protein dinosaur bone validate hypotheses about evolutionary...
The Birds and the Dinosaurs extent to which primary tissues are preserved in ancient fossils remains controversial. Schweitzer et al. (p. 626 ; see news story by Service ) describe well-preserved collagen sequences from femur of an 80-million-year-old hadrosaur. fossil structures resembling bone vessels. Both extracts tissue pieces were analyzed multiple laboratories mass spectrometry, revealed that support a close relation between birds dinosaurs.
ABSTRACT Histological evidence of the bones pterosaurs and dinosaurs indicates that typically large forms these groups grew at rates more comparable to those birds mammals than other living reptiles. However, Scutellosaurus, a small, bipedal, basal thyreophoran ornithischian dinosaur Early Jurassic, shows histological features in its skeletal tissues suggest relatively lower growth larger dinosaurs. In respects like small such as Orodromeus some birds, is young, rapidly growing crocodiles...
Histologic studies of embryonic and perinatal longbones living birds, non-avian dinosaurs, other reptiles show a strong phylogenetic signal in the distribution tissues patterns vascularization both shafts bone ends. The bones basal archosaurs have thin-walled cortices large marrow cavities that are sometimes subdivided by erosion rooms early stages growth. poorly vascularized, osteocyte lacunae common but randomly organized. Additionally, there is no evidence fibrolamellar tissue...
Soft tissues are preserved within hindlimb elements of Tyrannosaurus rex (Museum the Rockies specimen 1125). Removal mineral phase reveals transparent, flexible, hollow blood vessels containing small round microstructures that can be expressed from into solution. Some regions demineralized bone matrix highly fibrous, and possesses elasticity resilience. Three populations have cell-like morphology. Thus, some dinosaurian soft may retain their original flexibility, elasticity,
Tyrannosaurus rex is the most commonly found North American latest Cretaceous theropod, but until 1980s only five specimens had been discovered, and no more than six have received a full description. Consequently there has little information on how old were at maturity or death. Histological analysis of seven individuals provided, for first time, an opportunity to assess age represented by bone cortex, estimate average individual these skeletons, determine whether they fully grown...
Unambiguous indicators of gender in dinosaurs are usually lost during fossilization, along with other aspects soft tissue anatomy. We report the presence endosteally derived bone tissues lining interior marrow cavities portions Tyrannosaurus rex (Museum Rockies specimen number 1125) hindlimb elements, and we hypothesize that these homologous to specialized avian known as medullary bone. Because is unique female birds, its discovery extinct solidifies link between suggests similar...
Background Extended neoteny and late stage allometric growth increase morphological disparity between stages in at least some dinosaurs. Coupled with relatively low dinosaur density the Upper Cretaceous of North America, ontogenetic transformational representatives are often difficult to distinguish. For example, many hadrosaurids previously reported represent small lambeosaurine species were demonstrated be juveniles larger taxa. Marginocephalians (pachycephalosaurids + ceratopsids) undergo...
An external fundamental system (EFS) is a form of bone microstructure present in the outermost cortex long bones animals that have attained skeletal maturity. It indicates an effective cessation any significant periosteal growth (i.e., circumference or girth). Although EFS has been noted several reptile taxa, idea reptiles grow continually throughout their lives remains popular. Examination femoral from captive American Alligators (Alligator mississippiensis) reveals parallel-fibered tissue...
Background A dinosaur census recorded during the Hell Creek Project (1999–2009) incorporates multiple lines of evidence from geography, taphohistory, stratigraphy, phylogeny and ontogeny to investigate relative abundance large dinosaurs preserved in Upper Cretaceous Formation northeastern Montana, USA. Overall, skeletal assemblages (excluding lag-influenced records) consist primarily subadult or small adult size individuals. Small juveniles adults are both extremely rare, whereas individuals...
ABSTRACT Although they have been considered distinct genera for over a century, ontogenetic analyses reveal that Triceratops and "Torosaurus" actually represent growth stages of single genus. Major changes in cranial morphology—including the opening parietal fenestrae elongation squamosals—occur rapidly, very late ontogeny result characteristic 'Torosaurus' morphology. This report presents results 10-year field study dinosaurs Hell Creek Formation Montana is based on collection 50 specimens...
Abstract Fossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological 50 tibiae hadrosaurid dinosaur Maiasaura peeblesorum allows predictions annual growth and ecological interpretations based on more histologic data than any previous large study. Tibia length correlates well (R 2 >0.9) with diaphyseal circumference, cortical area, wall thickness,...
Bone microanalyses of extant vertebrates provide a necessary framework from which to form hypotheses regarding the growth and skeletochronology extinct taxa. Here, we describe bone microstructure quantify histovariability appendicular elements osteoderms three juvenile American alligators (Alligator mississippiensis) assess mark tissue organization within amongst individuals, with intention validating paleohistological interpretations. Results confirm previous observations that lamellar...