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| A reconstruction of a mamenchisaurid with a pathology evident in its left forelimb. |
Abstract
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.
Keywords: bone tumor, Eusauropod, lesion, neoplasm, periosteal reactive
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| Mamenchisaurid ulna PN14-108. (a) Gross external morphology of the ulna in lateral view. (b) Gross external morphology of the ulna in medial view. The box shows close-up images of the external area that connects intracortically. (c) A 3D reconstruction in posterior view based on CT data and virtual thin sections showing the pathologic bone. PL1 indicates a sagittal view, whereas P1–P3 indicates cross-sectional views. Scale bar equals 100 mm. |
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| A reconstruction of a mamenchisaurid with a pathology evident in its left forelimb. Artwork by Kmonvich Lawan. |
CONCLUSIONS:
The paleopathology in the ulna of the 150-million-year-old mamenchisaurid from Thailand is identified as having an osteogenic tumor in the posterior metaphysis of the bone. Using a combination of anatomical observations, CT scan data, and osteohistology of the afflicted region of the ulna, we can rule out several pathologies (such as osteosarcoma, osteomyelitis, intraosseous abscess, stress fracture, and hemangioma), but the nature of the specific pathology in the mamenchisaurid remains elusive. Definitive diagnoses of a bone pathology in modern animals can sometimes be extremely challenging (e.g., Maxie, 2015), especially because different bone tumors often have similar characteristics (e.g., Thompson & Dittmer, 2017). Thus, here we prefer to err on the side of caution, fully aware that we do not even have soft tissue to assist in the diagnosis. The osteohistological data permitted the identification of the individual as a subadult, that is, an individual that had passed its most rapid phase of growth but was still growing. In addition, using both the CT scan data and the histological sections, we were able to identify the fractures in the bone as unrelated to the pathologic response and likely caused by taphonomic damage to the bone. Overall, our findings contribute to knowledge of dinosaur paleopathologies and shed insight into the biology of basal sauropods.
Siripat Kaikaew, Suravech Suteethorn and Anusuya Chinsamy. 2025. Novel Report of An Osteogenic Tumor in a late Jurassic Mamenchisaurid from Thailand. Journal of Anatomy. DOI: doi.org/10.1111/joa.14266 [24 April 2025]
An isolated posterior cervical vertebra of a sauropod discovered at Phu Dan Ma (Kalasin Province, northeastern Thailand) is the first informative postcranial specimen from the Phu Kradung Formation, a Upper Jurassic to Lower Cretaceous continental unit. The vertebra is referred to the family Mamenchisauridae, otherwise mainly known from China. In addition, spatulate teeth from the same formation and a mid−dorsal vertebra from the Upper Jurassic Khlong Min Formation of southern Thailand are reassigned to this family. The occurrence of mamenchisaurids in the earliest Cretaceous of Thailand supports a hypothesis of geographical isolation of Central, Eastern, and Southeast Asia during the Late Jurassic. It also suggests that the main changes in their dinosaur assemblages occurred during the Early Cretaceous, rather than at the Jurassic–Cretaceous boundary.
Key words: Dinosauria, Mamenchisauridae, Jurassic, Cretaceous, Thailand.
Suravech Suteethorn, Jean Le Loeuff, Eric Buffetaut, Varavudh Suteethorn and Kamonrak Wongko. 2012. First evidence of a mamenchisaurid dinosaur from the Upper Jurassic–Lower Cretaceous Phu Kradung Formation of Thailand. Acta Palaeontologica Polonica. 58 (3): 459–469. DOI: doi.org/10.4202/app.2009.0155
