Histology of the heterostracan dermal skeleton: Insight into the origin of the vertebrate mineralised skeleton

ABSTRACT Cover illustration. The vertebrate mineralized skeleton and its canonical cell and tissue types are among the most formative innovations in vertebrate evolutionary history. Their origins, however, are poorly understood because living vertebrates either lack or possess all of the component mineralized skeletal systems in their entirety. In this issue of the Journal of Morphology Keating et al. (pp. 657–680) surveyed the dermal skeletal histology of heterostracans, inferred the plesiomorphic heterostracan skeleton and, through histological comparison to other skeletonising vertebrate clades, deduced the ancestral nature of the vertebrate dermal skeleton. The cover shows a transverse section through a cephalothoracic shield of Tesseraspis tesselata.