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Abstract：
Skeletal development is well known in temnospondyls, the most diverse group of Paleozoic and Mesozoic amphibians. However, the elements of carpus and tarsus (i.e., the mesopodium) were always the last bones to ossify relative to the other limb bones and with regard to the rest of the skeleton, and are preserved only in rare cases. Thus, in contrast to the other parts of the limb skeleton, little is known about the ontogeny and sequence of ossification of the temnospondyl carpus and tarsus. We intended to close this gap by studying the ontogenies of a number of Permo/Carboniferous stereospondylomorphs, the only temnospondyls with preserved growth series in which the successive ossification of carpals and tarsals can be traced. Studying the degree of mesopodial ossification within the same species show that it is not necessarily correlated with body size. This indicates that individual age rather than size determined the degree of mesopodial ossification in stereospondylomorphs and that the largest individuals are not necessarily the oldest ones. In the stereospondylomorph tarsus, the distal tarsals show preaxial development in accordance with most early tetrapods and salamanders. However, the more proximal mesopodials exhibit postaxial dominance, i.e., the preaxial column (tibiale, centrale 1) consistently started to ossify after the central column (centralia 2-4, intermedium) and the postaxial column (fibulare). Likewise, we observed preaxial development of the distal carpals in the stereospondylomorph carpus, as in most early tetrapods for which a statement can be made. However, in contrast to the tarsus, the more proximal carpals were formed by preaxial development, i.e., the preaxial column (radiale, centrale 1) ossified after the central column (centralia 2-4, intermedium) and before the postaxial column (ulnare). This pattern is unique among known early tetrapods and occurs only in certain extant salamanders. Furthermore, ossification proceeded from distal to proximal in the central column of the stereospondylomorph carpus, whereas the ossification advanced from proximal to distal in the central column of the tarsus. Despite these differences, a general ossification pattern that started from proximolateral (intermedium or centrale 4) to mediodistal (distal tarsal and carpal 1) roughly in a diagonal line is common to all stereospondylomorph mesopodials investigated. This pattern might basically reflect the alignment of stress within the mesopodium during locomotion. Our observations might point to a greater variability in the development of the mesopodium in stereospondylomorphs and probably other early tetrapods than in most extant tetrapods, possibly mirroring a similar variation as seen in the early phases of skeletogenesis in salamander carpus and tarsus.
摘要：
骨骼发育是众所周知的，最多样化的古生代和中生代两栖动物。然而,腕骨和关节的元素(即，相对于其他肢体骨骼和骨骼的其余部分，只在极少数情况下保存。因此，与肢体骨骼的其他部分相反，对temnospondyl腕骨和tar骨的个体发育和骨化顺序知之甚少。我们打算通过研究许多二叠纪/石炭纪立体脊椎的个体发育来缩小这一差距，唯一具有保留的生长系列的temnospondyls，可以追踪腕骨和tarsals的连续骨化。研究同一物种中的中骨骨化程度表明，它不一定与体型相关。这表明个体年龄而不是大小决定了立体脊椎骨化的中足骨化程度，并且最大的个体不一定是最老的个体。在立体脊椎上，远端tarsals显示前轴发育，与大多数早期四足动物和sal一致。然而,近端中足骨显示后轴优势，即，前轴柱(胫骨，中心1）在中心柱（中心2-4，中间柱）和后轴柱（腓骨）之后始终开始骨化。同样，我们观察到立体脊椎形态腕骨远端腕骨的轴前发育，就像大多数早期四足动物一样，可以对此发表声明。然而,与tarus相反，较近端的腕骨是由前轴发育形成的，即，前轴柱(收音机，中心1）在中心柱（中心2-4，中间）之后和后轴柱（ulnare）之前僵化。这种模式在已知的早期四足动物中是独特的，并且仅在某些现存的sal中发生。此外，骨化在立体脊椎的中央柱中从远端到近端进行，而骨化在骨中央柱中从近端向远端推进。尽管存在这些差异,从近端外侧（中间或中央4）开始到中端（远骨和腕骨1）大致在对角线上的一般骨化模式在所有研究的立体上都是常见的。这种模式可能基本上反映了运动过程中中膜内应力的排列。我们的观察结果可能表明，与大多数现存的四足动物相比，立体脊椎和其他早期四足动物中的中足动物的发育差异更大，可能反映了与sal鱼和tar骨形成早期相似的变化。
