Data_Sheet_1_Diversity and Evolution of Mineralized Skeletal Tissues in Chondrichthyans.PDF

The diversity of skeletal tissues in extant vertebrates includes mineralized and unmineralized structures made of bone, cartilage, or tissues of intermediate nature. This variability, together with the diverse nature of skeletal tissues in fossil species question the origin of skeletonization in early vertebrates. In particular, the study of skeletal tissues in cartilaginous fishes is currently mostly restrained to tessellated cartilage, a derived form of mineralized cartilage that evolved at the origin of this group. In this work, we describe the architectural and histological diversity of neural arch mineralization in cartilaginous fishes. The observed variations in the architecture include tessellated cartilage, with or without more massive sites of mineralization, and continuously mineralized neural arches devoid of tesserae. The histology of these various architectures always includes globular mineralization that takes place in the cartilaginous matrix. In many instances, the mineralized structures also include a fibrous component that seems to emerge from the perichondrium and they may display intermediate features, ranging from partly cartilaginous to mostly fibrous matrix, similar to fibrocartilage. Among these perichondrial mineralized tissues is also found, in few species, a lamellar arrangement of the mineralized extracellular matrix. The evolution of the mineralized tissues in cartilaginous fishes is discussed in light of current knowledge of their phylogenetic relationships.

现生脊椎动物的骨骼组织多样性包含由骨、软骨或中间类型组织构成的矿化与非矿化结构。这种组织多样性，加之化石物种中骨骼组织的多样特征，对早期脊椎动物骨骼化的起源问题构成了研究疑问。具体而言，当前对软骨鱼类骨骼组织的研究大多局限于镶嵌软骨（tessellated cartilage）——一种在该类群起源时演化出的衍生型矿化软骨。本研究针对软骨鱼类的椎弓矿化结构与组织学多样性展开描述。观察到的结构变异包括带有或不带大型矿化位点的镶嵌软骨，以及无镶嵌片的连续矿化椎弓。这些不同结构的组织学特征均包含发生于软骨基质中的球状矿化过程。在多数案例中，这类矿化结构还包含似乎源自软骨膜（perichondrium）的纤维成分，且可呈现介于部分软骨基质与近乎全纤维基质之间的中间特征，与纤维软骨（fibrocartilage）类似。在少数物种的这类软骨膜源性矿化组织中，还可见矿化细胞外基质呈层状排列的结构。本研究结合当前对软骨鱼类系统发育关系的认知，探讨了其矿化组织的演化历程。