CR2P, MNHN-CNRS-Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France.
J Anat. 2019 Dec;235(6):1105-1113. doi: 10.1111/joa.13070. Epub 2019 Jul 29.
The dermoskeleton of the earliest vertebrates is well known but their endoskeleton is thought to have been largely cartilaginous until the Late Silurian. We confirm that the dermal plates of Astraspis are three-layered, with a superficial layer of enameloid and orthodentine, a middle layer of aspidin and a basal layer of lamellar acellular bone. This dermoskeleton is found in association with globular calcified cartilage, indicating the presence of a partially mineralized endoskeleton. In addition to the classical three-layered organization, some dermal plates exhibit alignments of chondrocyte-like lacunae, very similar to a pattern typical of chondroid metaplastic bone, previously unknown in early vertebrates. This discovery implies the presence of a proliferative cartilage, hitherto only known in Osteichthyans. This discovery indicates that a pattern similar to the first step of endochondral ossification was already present in the earliest vertebrates.
最早的脊椎动物的皮-骨骼结构为人熟知，但其内骨骼据信在志留纪晚期以前主要为软骨质。我们证实，Astraspis 的真皮板为三层结构，表层为釉质质和正真牙质，中层为棘层，基底层为板层无细胞骨。这种皮-骨骼结构与球形钙化软骨相关，表明存在部分矿化的内骨骼。除了经典的三层组织结构外，一些真皮板显示出类似于软骨样陷窝的排列，与先前在早期脊椎动物中未知的软骨样骨转化骨的典型模式非常相似。这一发现表明存在增殖软骨，迄今为止仅在硬骨鱼类中被发现。这一发现表明，类似软骨内骨化第一步的模式在最早的脊椎动物中已经存在。
