Novel report of an osteogenic tumor in a late Jurassic Mamenchisaurid from Thailand.

Here we report on an osseous abnormality and multiple fractures in an ulna of a subadult basal Eusauropod (Mamenchisauridae) from the Late Jurassic Phu Kradueng Formation in Thailand. The anatomical deformities were studied using a multi-method approach that included an assessment of its gross morphology, computed tomography (CT), and osteohistology to aid in its diagnosis. The intracortical lesion in the bone is irregularly shaped, has well-defined margins with scattered irregular bony trabeculae especially in its center, and it is surrounded by sclerotic bone and spiculated periosteal reactive tissue. The analysis of the radiology and the histopathological characteristics indicates that the lesion in the ulna is an osteogenic tumor, although we are unable to confidently commit to a more specific diagnosis. CT scan data indicated that the multiple fractures evident in the ulna occurred postmortem and are unrelated to the pathology. This is the first report of an osteogenic tumor in a basal Eusauropoda.