aspidin

Japanese: aspidin

…The carapace of the head is called the carapace, and the carapace of the chest is called the thorax. The main body of these carapaces was bone, but they were slightly different from the bones of modern vertebrates in that they did not contain bone cells, and so they are also called aspidins to distinguish them. There was a species in which the surface of this bone plate was completely covered with something similar to teeth, like the surface of the body of modern sharks. …

From [Bones]

…The dermal bone was probably a defense against aquatic invertebrates at the time, and is thought to have formed in the dermis as an appendage (dermal bone), as described later. However, this dermal bone was not necessarily the same as the bones of modern vertebrates, and was often made of a bone-like tissue called aspidin. This was probably a precursor of bone, since it did not contain cellular elements and had no self-remodeling properties. …

*Some of the terminology that mentions "aspidin" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…頭部の甲を頭甲，胸部の甲を胸甲という。これらの甲の本体は骨だったが，現在の脊椎動物の骨とは少し異なって骨細胞を含まないものだったため，区別してアスピディンaspidinとも呼ばれる。この骨板の表面を現在のサメの体表のように，歯と同様のものが覆いつくしている種類があった。…

【骨】より

…皮甲はおそらく当時の水生無脊椎動物に対する防護物で，のちに述べるような〈付加骨(皮骨dermal bone)〉として真皮の中に形成されたものと考えられている。もっともこの皮甲は現在の脊椎動物がもつ骨と必ずしも同じものではなく，〈アスピディンaspidin〉と呼ばれる骨に類似の組織でできている場合が多かった。これは，その内部に細胞要素を含まず自己改造の性質をもたないものだったため，骨の先駆体だったのだろうと考えられる。…

※「aspidin」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典第２版について | 情報

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