Figure 1.

Phylogenetic relationships of the principal vertebrate groups from Donoghue and Keating (2014). Labelled internal branches refer to acquisition of key skeletal apomorphies. Origin of the vertebrate skeleton consisting of a splanchnocranium, neurocranium, fin rays and arcualia (A); origin of a mineralised dermal skeleton and of the canonical vertebrate mineralised tissues: bone, dentine and enameloid (B); origin of a mineralised neurocranium (C); cellular dermal and perichondral bone, neurocranium includes elements equivalent to the scapula and coracoid (D); mineralised splanchnocranium, evolution of jaws and pelvic girdle (E); mineralised axial skeleton (F), mineralised fin radials, teeth associated with spanchnocranium (G); and endochondral bone (H).