Fig. 3: Middle Ordovician agnathan vertebrates Eriptychius and Astrapis odontode microanatomy.

a, Three-dimensional reconstruction of a fragment of dermal armor of the agnathan Eriptychius sp. (FMNH PF 17901) showing the elongated odontodes, the transverse section indicating the relative region of c ; b, Three-dimensional reconstruction of a fragment of dermal armor of the agnathan Astrapis sp. (FMNH PF 17898) showing the rounded and stellate shaped odontodes, the transverse section indication the relative region of d. c, A transverse tomographic section of Eriptychius sp. odontodes exhibiting a lack of enameloid, wide caliber dentine tubules, pulp cavity and vascular canals;. d, A transverse tomographic section of Astraspis sp. odontodes exhibiting a thick layer of enameloid, narrow caliber dentine tubules, pulp cavity and vascular canals;. e,f, Three-dimensional reconstruction showing the internal anatomy of Eriptychius sp. and Astraspis sp., note the lack of enamel, wide caliber dentine tubules and extensive vascularity of Eriptychius sp. Abbreviations: od, odontode; dt, dentine tubule; pc, pulp cavity; vc, vascular canal; en, enameloid. Scalebars=100 μm.