Figure 2: Probable tendons/ligaments and fibrocartilages in the Confuciusornis ankle.
From: Cellular preservation of musculoskeletal specializations in the Cretaceous bird Confuciusornis
The intertarsal joint region of the specimen MES-NJU 57002 (Fig. 1f,g). (a) BSE-SEM image of the square area in Fig. 1f, showing the tarsometatarsus at the top right of the image and the tibiotarsus on the left, with intervening tendon/ligament material (t/l). Within the tendon/ligament, there are regions of fibrocartilage matrix (fc) and cells (arrows) arranged in rows between parallel fibres. (b) Close-up view of the square area in a. (c) BSE-SEM image of the square area in Fig. 1g, showing the tibiotarsus on the left and the tarsometatarsus on the right. A large area of mineralization (m) is visible in the fibrocartilage on the plantar aspect of the ankle joint. (d) Close-up view of the square area in c. Cellular structures (arrows) are embedded in a matrix composed of network of interwoven fibres and smaller mineralizations. (e) BSEM images show that the articular facets of the tarsometatarsus and tibiotarsus in the Confuciusornis specimen contain two thin layers of densely packed, paired cellular structures: an inner calcified layer (yellow arrows) and an outer uncalcified layer (blue arrows). (f) Close-up view of the square area in e. Scale bar, 200 μm in a and c, 100 μm in e, 50 μm in b, 10 μm in d, 20 μm in f.
