@article{schweitzer_wittmeyer_horner_2007, title={Soft tissue and cellular preservation in vertebrate skeletal elements from the Cretaceous to the present}, volume={274}, ISSN={["1471-2954"]}, DOI={10.1098/rspb.2006.3705}, abstractNote={
            Soft tissues and cell-like microstructures derived from skeletal elements of a well-preserved
            Tyrannosaurus rex
            (MOR 1125) were represented by four components in fragments of demineralized cortical and/or medullary bone: flexible and fibrous bone matrix; transparent, hollow and pliable blood vessels; intravascular material, including in some cases, structures morphologically reminiscent of vertebrate red blood cells; and osteocytes with intracellular contents and flexible filipodia. The present study attempts to trace the occurrence of these four components in bone from specimens spanning multiple geological time periods and varied depositional environments. At least three of the four components persist in some skeletal elements of specimens dating to the Campanian. Fibrous bone matrix is more altered over time in morphology and less likely to persist than vessels and/or osteocytes. Vessels vary greatly in preservation, even within the same specimen, with some regions retaining pliability and other regions almost crystalline. Osteocytes also vary, with some retaining long filipodia and transparency, while others present with short and stubby filipodia and deeply pigmented nuclei, or are pigmented throughout with no nucleus visible. Alternative hypotheses are considered to explain the origin/source of observed materials. Finally, a two-part mechanism, involving first cross-linking of molecular components and subsequent mineralization, is proposed to explain the surprising presence of
            still
            -soft elements in fossil bone. These results suggest that present models of fossilization processes may be incomplete and that soft tissue elements may be more commonly preserved, even in older specimens, than previously thought. Additionally, in many cases, osteocytes with defined nuclei are preserved, and may represent an important source for informative molecular data.
          }, number={1607}, journal={PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES}, author={Schweitzer, Mary Higby and Wittmeyer, Jennifer L. and Horner, John R.}, year={2007}, month={Jan}, pages={183–197} }
 @article{schweitzer_wittmeyer_horner_2005, title={Gender-specific reproductive tissue in ratites and Tyrannosaurus rex}, volume={308}, ISSN={["0036-8075"]}, DOI={10.1126/science.1112158}, abstractNote={
            Unambiguous indicators of gender in dinosaurs are usually lost during fossilization, along with other aspects of soft tissue anatomy. We report the presence of endosteally derived bone tissues lining the interior marrow cavities of portions of
            Tyrannosaurus rex
            (Museum of the Rockies specimen number 1125) hindlimb elements, and we hypothesize that these tissues are homologous to specialized avian tissues known as medullary bone. Because medullary bone is unique to female birds, its discovery in extinct dinosaurs solidifies the link between dinosaurs and birds, suggests similar reproductive strategies, and provides an objective means of gender differentiation in dinosaurs.
          }, number={5727}, journal={SCIENCE}, author={Schweitzer, MH and Wittmeyer, JL and Horner, JR}, year={2005}, month={Jun}, pages={1456–1460} }
 @article{avci_schweitzer_boyd_wittmeyer_arce_calvo_2005, title={Preservation of bone collagen from the late cretaceous period studied by immunological techniques and atomic force microscopy}, volume={21}, ISSN={["0743-7463"]}, DOI={10.1021/la047682e}, abstractNote={Late Cretaceous avian bone tissues from Argentina demonstrate exceptional preservation. Skeletal elements are preserved in partial articulation and suspended in three dimensions in a medium-grained sandstone matrix, indicating unusual perimortem taphonomic conditions. Preservation extends to the microstructural and molecular levels. Bone tissues respond to collagenase digestion and histochemical stains. In situ immunohistochemistry localizes binding sites for avian collagen antibodies in fossil tissues. Immunohistochemical studies do not, however, guarantee the preservation of molecular integrity. A protein may retain sufficient antigenicity for antibody binding even though degradation may render it incapable of original function. Therefore, we have applied atomic force microscopy to address the integrity and functionality of retained organic structures. Collagen pull-off measurements not only support immunochemical evidence for collagen preservation for antibody recognition but also imply preservation of the whole molecular integrity. No appreciable differences in collagen pull-off properties were measured between fossil and extant bone samples under physiological conditions.}, number={8}, journal={LANGMUIR}, author={Avci, R and Schweitzer, MH and Boyd, RD and Wittmeyer, JL and Arce, FT and Calvo, JO}, year={2005}, month={Apr}, pages={3584–3590} }
 @article{schweitzer_wittmeyer_horner_toporski_2005, title={Soft-tissue vessels and cellular preservation in Tyrannosaurus rex}, volume={307}, ISSN={["1095-9203"]}, DOI={10.1126/science.1108397}, abstractNote={
            Soft tissues are preserved within hindlimb elements of
            Tyrannosaurus rex
            (Museum of the Rockies specimen 1125). Removal of the mineral phase reveals transparent, flexible, hollow blood vessels containing small round microstructures that can be expressed from the vessels into solution. Some regions of the demineralized bone matrix are highly fibrous, and the matrix possesses elasticity and resilience. Three populations of microstructures have cell-like morphology. Thus, some dinosaurian soft tissues may retain some of their original flexibility, elasticity, and resilience.
          }, number={5717}, journal={SCIENCE}, author={Schweitzer, MH and Wittmeyer, JL and Horner, JR and Toporski, JK}, year={2005}, month={Mar}, pages={1952–1955} }
 @article{avci_schweitzer_boyd_wittmeyer_steele_toporski_beech_arce_spangler_cole_et al._2004, title={Comparison of antibody-antigen interactions on collagen measured by conventional immunological techniques and atomic force microscopy}, volume={20}, ISSN={["0743-7463"]}, DOI={10.1021/la036376i}, abstractNote={We have developed a means of using atomic force microscopy (AFM) to repeatedly localize a small area of interest (4 x 4 microm(2)) within a 0.5-cm(2) area on a heterogeneous sample, to obtain and localize high-resolution images and force measurements on nonideal samples (i.e., samples that better reflect actual biological systems, not prepared on atomically flat surfaces). We demonstrate the repeated localization and measurement of unbinding forces associated with antibody--antigen (ab--ag) interactions, by applying AFM in air and in liquid to visualize and measure polyclonal ab--ag interactions, using chicken collagen as a model system. We demonstrate that molecular interactions, in the form of ab--ag complexes, can be visualized by AFM when secondary antibodies are conjugated to 20-nm colloidal gold particles. We then compare those results with established immunological techniques, to demonstrate broader application of AFM technology to other systems. Data from AFM studies are compared with results obtained using immunological methods traditionally employed to investigate ab--ag interactions, including enzyme-linked immunosorbent assay, immunoblotting, and in situ immunofluorescence. Finally, using functionalized AFM tips with a flexible tether [poly(ethylene glycol) 800] to which a derivatized antibody was attached, we analyzed force curve data to measure the unbinding force of collagen antibody from its antigen, obtaining a value of approximately 90 +/- 40 pN with a MatLab code written to automate the analyses of force curves obtained in force--volume mode. The methodology we developed for embedded collagen sections can be readily applied to the investigation of other receptor--ligand interactions.}, number={25}, journal={LANGMUIR}, author={Avci, R and Schweitzer, M and Boyd, RD and Wittmeyer, J and Steele, A and Toporski, J and Beech, W and Arce, FT and Spangler, B and Cole, KM and et al.}, year={2004}, month={Dec}, pages={11053–11063} }