(a) Vertebrate phylogenetic tree, highlighting in green extant and extinct taxonomic groups capable of complete appendage regeneration among actinopterygians (Polypterus), sarcopterygian fish (lungfish) and tetrapods (salamanders, Micromelerpeton and Microbrachis). (b) Pectoral fin regeneration monitored for 30 wpa in an adult L. paradoxa specimen. (c,f) At 1 wpa, formation of a WE occurs with minimal mitosis. (d,g) At 2 wpa, AEC forms and cells accumulate distally and form a blastema, cell proliferation occurs in regions flanking the cartilage and in the blastema. (e,h) At 3 wpa, blastema extends distally, new cartilage is forming and cell proliferation intensifies. Haematoxylin and eosin stained sections are shown (c–e). Proliferating cells during fin regeneration are shown (green), the nuclei of all cells is stained (blue) (f–h). Dashed lines denote amputation planes. Asterisk denotes newly formed cartilage. Scale bars of 10 mm (b), 1 mm (c,f) and 0.5 mm (d,e,g,h). Ca, cartilage; Bl, blastema; Ma, million years ago.