Fig. 2

Developmental details of the caudal fin skeleton in stickleback, zebrafish, spotted gar, bowfin, and American paddlefish. A‐D: Three‐spined stickleback (Gasterosteus aculeatus), 6.5 mm TL (A), 7 mm TL (B), 7.5 mm TL (C) and 15 mm TL (D). E‐H: Zebrafish (Danio rerio) 4.5 mm TL (E), 5 mm TL (F), 5.5 mm TL (G), and 6 mm TL (H). I‐L: Spotted gar (Lepisosteus oculatus), 17 mm TL (I), 19 mm TL (J), 26 mm TL (K), and 85 mm TL (L). M,N: Bowfin (Amia calva), 34 mm TL (M‐M″) and 99 mm TL (N). O‐Q: American paddlefish (Polyodon spathula), 12 mm TL (O), 65 mm TL (P‐P′) and 85 mm TL (Q). L: Detail of the posterior part of the notochord of Fig. 1J. For each species, the white elongated triangle indicates hypural 1 as a reference. In A‐L the black arrow points at the hypural diastema. In the insert in N, the oval circles the distal ends of hypurals 2 and 3 showing an unbroken plate of connective tissue. act, actinotrichia; bd, basidorsal arcualia; bv, basiventral arcualia; bva, basiventral autocentra; cfr, caudal fin rays; darc, dorsal arcualia; dcr, distal caudal radials; ecfr, epichordal caudal fin rays; ep, epurals; ep1+2, compound epural made by the fusion of epurals 1 and 2; f‐phy, foramen created by the parhypural; fub, basal fulcra; ha, haemal arches; hd, hypural diastema; hs, haemal spines; hyp1?, putative hypural 1; h10, hypural 10; h20, hypural 20; h30, hypural 30; id, interdorsal arcualia; iv, interventral arcualia; oc, opisthural cartilage; n‐hyp1, notch at the base of hypural 1; na, neural arches; nc, notochord; nc‐f, notochord point of flexion; ns, neural spine; phy, parhypural; pct, plate of connective tissue; pcta, anterior plate of connective tissue; pctp, posterior plate of connective tissue; p‐pHP2, anterior process of the posterior hypural plate; pu1+u1, compound centrum made by the fusion of preural centrum 1 and ural centrum 1; pu2+3, compound centrum made by the fusion of preural centra 2 and 3; pu1+u1+u2, compound centrum made by the fusion of preural centrum 1 and ural centra 1 and 2; sncf, supraneurals of the caudal fin skeleton; un, uroneural; una, ural neural arch; ust, urostyle; u3, ural centrum 3.