2024-04-02 ペンシルベニア州立大学(PennState)
<関連情報>
- https://www.psu.edu/news/eberly-college-science/story/evolution-walking-hip-bone-connected-rib-bones/
- https://www.pnas.org/doi/10.1073/pnas.2316106121
ティクタリック・ローゼの軸骨格 The axial skeleton of Tiktaalik roseae
Thomas A. Stewart, Justin B. Lemberg, Emily J. Hillan, +2, and Neil H. Shubin
Proceedings of the National Academy of Sciences Published:April 2, 2024
DOI:https://doi.org/10.1073/pnas.2316106121
Significance
The origin of terrestrial vertebrates is marked by changes to the entire post-cranial skeleton. To date, information on the vertebrae and ribs of the closest relatives to limbed vertebrates has been limited, making it difficult to reconstruct how the axial skeleton was evolving. This paper describes the axial column of Tiktaalik roseae, a close relative of limbed vertebrates. The holotype specimen was µCT (micro-computed tomography) scanned, which revealed its vertebrae and posterior ribs. These data show how specialization for head mobility, body support, and pelvic fin buttressing arose in stem tetrapods, allowing for a three-dimensional reconstruction of Tiktaalik and shedding light on the antecedents to the terrestrial walking behaviors.
Abstract
The axial columns of the earliest limbed vertebrates show distinct patterns of regionalization as compared to early tetrapodomorphs. Included among their novel features are sacral ribs, which provide linkage between the vertebral column and pelvis, contributing to body support and propulsion by the hindlimb. Data on the axial skeletons of the closest relatives of limbed vertebrates are sparce, with key features of specimens potentially covered by matrix. Therefore, it is unclear in what sequence and under what functional context specializations in the axial skeletons of tetrapods arose. Here, we describe the axial skeleton of the elpistostegalian Tiktaalik roseae and show that transformations to the axial column for head mobility, body support, and pelvic fin buttressing evolved in finned vertebrates prior to the origin of limbs. No atlas–axis complex is observed; however, an independent basioccipital–exoccipital complex suggests increased mobility at the occipital vertebral junction. While the construction of vertebrae in Tiktaalik is similar to early tetrapodomorphs, its ribs possess a specialized sacral domain. Sacral ribs are expanded and ventrally curved, indicating likely attachment to the expanded iliac blade of the pelvis by ligamentous connection. Thus, the origin of novel rib types preceded major alterations to trunk vertebrae, and linkage between pelvic fins and axial column preceded the origin of limbs. These data reveal an unexpected combination of post-cranial skeletal characters, informing hypotheses of body posture and movement in the closest relatives of limbed vertebrates.
