Abstract
Abstract The Cretaceous Two Medicine Formation of northwestern Montana has yielded blocky, calcareous coprolites that contain abundant fragments of conifer wood and were produced by large herbivorous dinosaurs. The coprolites are generally dark gray to black in color due to a dark substance confined chiefly within what originally were the capillaries of tracheid and ray cells of xylem. This substance is a kerogen that consists in part of thin-walled vesicles 0.1–1.3 μm in diameter. Pyrolysis products of this kerogen are diagnostic of a bacterial origin with a possible contribution from terrestrial plants. The vesicular component is interpreted as the residue of bacterial cells, whereas a second filamentous component, closely associated with the vesicles, may be the residue of an extracellular binding material, such as glycocalyx. At least two episodes of calcification of the coprolite are recognized by manganous cathodoluminescence. The earlier of these infilled the capillary channels of the conifer fragm...
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