Long bone histology of Metoposaurus diagnosticus (Temnospondyli) from the Late Triassic of Krasiejów (Poland) and its paleobiological implications

ABSTRACT

Long bones of the temnospondyl Metoposaurus diagnosticus krasiejowensis from the Late Triassic of Krasiejów, Poland, were studied using histological analysis. Six femora, three humeri, a radius, and an ulna were prepared for thin-sectioning. In all bones, the dominant type of primary bone matrix is parallel-fibered bone with secondary, or rarely primary, deposition of lamellar bone inside vascular canals. Two small humeri and the smallest femur showed incipient fibrolamellar bone, which may be a character typical for juvenile individuals. The medullary region is filled with well-developed trabecular bone. The growth marks in all bones are organized as thick layers of highly vascularized zones and thick compact annuli with numerous rest lines, which may correspond with favorably wet and long, unfavorably dry seasons. The thickness of the annuli is similar to the thickness of zones for reasons still unknown. Based on the highest estimated number of growth cycles in the femora, the long bones from Krasiejów all belong to juvenile animals. High amounts of Sharpey's fibers are very characteristic in all described bones. A new interpretation of mode of life is proposed based on these findings: the extremely flat skull, the relatively short and wide humerus, large manus, and limbs with strong muscles suggest that this species might have been able to burrow underground during the long unfavorable part of the year.

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ACKNOWLEDGMENTS

We thank O. Dülfer and K. Waskow (University of Bonn) for preparing thin-sections and G. Oleschinski for microanatomical photos. We are grateful to J. Mitchell (University of Bonn) for improving the English. The constructive discussion and access to Dutuitosaurus material by V. de Buffrénil and J. Sébastian Steyer (Museum National d’Histoire Naturelle, Paris) are appreciated. A. Bodzioch from University of Opole is thanked for access and permission for sectioning of the Metoposaurus material. We thank all reviewers (S. Sanchez and anonymous) and editors for all comments. D.K.M. designed the research; D.K.M. and P.M.S. performed the research, analyzed data, and wrote the paper. This research was partially funded by the Deutsche Forschungsgemeinschaft (grants to P.M.S.) and by the Polish Ministry of Science and Higher Education (third edition of program: Support of International Mobility of Researchers for D.K.M.). The authors also thank the Self-Government of the Opole Voivodeship, Association Dinopark, and Association Delta for financial support of the excavation camps at Krasiejów.

Handling editor: Jason Anderson