NSRRC Activity Report 2022

044 NSRRC ACTIVITY REPORT 2022 TLS 01A1 White X-ray TLS 01B1 X-ray Microscopy • High-resolution X-ray Tomography, High-precision 3D Reconstruction Algorithm • Paleontology, Geosciences, Materials Science, Environmental Science References 1. D. Chen, H. Blom, S. Sanchez, P. Tafforeau, P. E. Ahlberg, Nature 539 , 237 (2016). 2. M. Zhu, W. Zhao, L. Jia, J. Lu, T. Qiao, Q. Qu, Nature 458 , 469 (2009). 3. P. S. Andreev, I. J. Sansom, Q. Li, W. Zhao, J. Wang, C.-C. Wang, L. Peng, L. Jia, T. Qiao, M. Zhu, Nature 609 , 964 (2022). 4. C.-C. Wang, Sci. Rep. 10 , 7330 (2020). 5. P. S. Andreev, I. J. Sansom, Q. Li, W. Zhao, J. Wang, C.-C. Wang, L. Peng, L. Jia, T. Qiao, M. Zhu, Nature 609 , 969 (2022). chondrichthyan, implying that jawed vertebrates were already quite diverse during the Early Silurian In contrast, the isolated scales, shield armor, and fin spines ( Fig. 2 ) were identified as belonging to a primitive chondrichthyan fish named Fanjingshania renovata . 5 Fanjingshania has skin ossifications of the shoulder region and is anatomically close to groups of extinct acanthodians. Interestingly, the authors found that the fossil bones of Fanjingshania show extensive resorption and remodeling, which is typically associated with bony fish skeletal development ( Fig. 2 ). X-ray tomography slices further reveal that this resorption was followed by deposition of replacement crown elements. However, unlike both extinct and living bony fishes, the resorption did not target individual teeth or skin denticles but instead removed a large area that included multiple skin denticles. This replacement mechanism is much more similar to skeletal repair than typical tooth or skin denticle substitution in bony fishes. Hard tissue modification is unprecedented in chondrichthyan fishes, implying that the developmental plasticity of the mineralized skeleton at the onset of jawed fish diversification is greater than previously understood. Also, Fanjingshania may be a transitional species between cartilaginous fishes and bony fishes, which implies that there may have been bony fishes at that time. The discoveries of this study provide strong evidence that jawed vertebrates appeared as early as 439 million years ago in the Early Silurian, 14 million years earlier than suggested by previously discovered fossils. This result greatly shortens the time gap between the fossil record and the molecular clock analysis estimation of the differentiation of jawed vertebrates to approximately 11 million years. In other words, these results provide further support for the molecular clock analysis prediction that jawed vertebrates should have appeared no later than 450 million years ago. These findings indicate that the vertebrate jaw, including that of humans, may have originated earlier (in the Late Ordovician). These novel findings rewrite existing vertebrate evolutionary models and, furthermore, will substantially influence how evolutionary rates of early vertebrates are assessed. (Reported by Chun-Chieh Wang) This report features the works of Ming Chu, Ivan J. Sansom, Chun-Chieh Wang and their co-workers published in Nature 609 , 964 (2022) and Nature 609 , 969 (2022). These papers were selected as the cover of issue 7929. Fig. 2 : Resorption features in the dermal skeleton of F. renovata . (a) Trunk scale with an anterior replacement odontode revealing the resorption surfaces in the scale crown and base. (b) An asymmetrical trunk scale and the crown and base of the same specimen in crown aspect demonstrating an absence of resorption surfaces in contrast to (a). [Reproduced from Ref. 5] (a) (b)