The earliest segmental sternum in a Permian synapsid and its implications for the evolution of mammalian locomotion and ventilation

The sternum is a stabilizing element in the axial skeleton of most tetrapods, closely linked with the function of the pectoral girdle of the appendicular skeleton. Modern mammals have a distinctive sternum characterized by multiple ossified segments, the origins of which are poorly understood. Altho...

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Bibliographic Details
Published in:Scientific reports 2022-08, Vol.12 (1), p.13472-9, Article 13472
Main Authors: Bendel, Eva-Maria, Kammerer, Christian F., Luo, Zhe-Xi, Smith, Roger M. H., Fröbisch, Jörg
Format: Article
Language:English
Subjects:
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631/181/414
Axial skeleton
Biological Evolution
Evolution
Fossils
Gait
Humanities and Social Sciences
Locomotion
Mammals
Morphology
multidisciplinary
Permian
Respiration
Rib cage
Science
Science (multidisciplinary)
Sternum
Sternum - anatomy & histology
Synapsida
Triassic
Ventilation
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Summary:The sternum is a stabilizing element in the axial skeleton of most tetrapods, closely linked with the function of the pectoral girdle of the appendicular skeleton. Modern mammals have a distinctive sternum characterized by multiple ossified segments, the origins of which are poorly understood. Although the evolution of the pectoral girdle has been extensively studied in early members of the mammalian total group (Synapsida), only limited data exist for the sternum. Ancestrally, synapsids exhibit a single sternal element and previously the earliest report of a segmental sternum in non-mammalian synapsids was in the Middle Triassic cynodont Diademodon tetragonus . Here, we describe the well-preserved sternum of a gorgonopsian, a group of sabre-toothed synapsids from the Permian. It represents an ossified, multipartite element resembling the mammalian condition. This discovery pulls back the origin of the distinctive “mammalian” sternum to the base of Theriodontia, significantly extending the temporal range of this morphology. Through a review of sternal morphology across Synapsida, we reconstruct the evolutionary history of this structure. Furthermore, we explore its role in the evolution of mammalian posture, gait, and ventilation through progressive regionalization of the postcranium as well as the posteriorization of musculature associated with mammalian breathing.
ISSN:2045-2322
2045-2322
DOI:10.1038/s41598-022-17492-6