The hypothesis of disease-related large mammal extinction has new support. A unique pathologic zone of resorption was first noticed in a Hiscock Mammut americanum metacarpal. The pathognomonic zone of resorption was present in fifty-nine (52%) of 113 skeletons with feet available for examination. Metacarpals and metatarsals were most commonly affected. Associated rib periosteal reaction is highly suggestive of tuberculosis and the foot lesions were identical to that documented in Bison as pathognomonic for tuberculosis. Recognizing that only a portion of animals infected by infectious tuberculosis develop bone involvement, the high frequency of the pathology in M. americanum suggests that tuberculosis was not simply endemic, but actually pandemic, a hyperdisease. Pandemic tuberculosis was one of several probable factors contributing to mastodon extinction.
New specimens of Cooksonia and Hostinella are described from the Bertie Group of Ontario and New York State, which is dated by faunas as latest Silurian (P ídolí). The rare plant fossils are unusual in that they are preserved in fine-grained, slightly argillaceous dolostones ('waterlime') rather than clastic rocks. At least two species of Cooksonia are present, one with ± globular sporangial morphology close to C. hemisphaerica Lang. Those with ellipsoidal/ discoidal sporangia are compared with C. pertoni Lang, C . paranensis Gerrienne et al . and C. bohemica Schweitzer, the latter represented by a single specimen from the P ídolí of the Czech Republic. However, the paucity of specimens, which prevents assessment of taphonomic influences on shape, combined with the absence of any anatomical features and the gross morphological simplicity of the fossils, precludes specific assignment. Specimens of Hostinella include one in which apices and a lateral basal structure resembling a root are preserved. It is concluded that the Laurentian assemblage of Ontario and New York State is less diverse and disparate than coeval assemblages, which are also preserved in marine rocks. Its preservation in limestones may have been facilitated by the hypersalinity inferred from various sedimentary features, which would restrict the activity of many decomposers.
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