A new mineralized tissue in the early vertebrate Astraspis.
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.
['Lemierre|Alfred|A|0000-0003-1755-3018', 'Germain|Damien|D|0000-0002-7608-2212']
D000818:Animals D005075:Biological Evolution D001842:Bone and Bones D002113:Calcification, Physiologic D002356:Cartilage D005580:Fossils D014714:Vertebrates
dermal bone histology pteraspidomorph skeleton