Extended Data Fig. 1: Growth series of Alligator mississippiensis embryonic pelvis, hindlimb and tail stained for cartilage and connective tissue.
From: The developing bird pelvis passes through ancestral dinosaurian conditions

A. Cartilage precursor and early cartilage (SOX-9, green) and cartilage (collagen II, blue). Approximate embryonic stages, top to bottom: F13 (15 days), F14 (16–17 days), F15 (18–20 days), F17 (22–23 days), F18 (25–26 days), F19 (27–28 days). B. Cartilage (collagen II, blue) and connective tissue (collagen I, purple). Approximate embryonic stages, top to bottom: F13 (15 days), F14 (16–17 days), F15 (18–20 days), F16 (21 days), F17 (22–23 days), F19 (27–28 days). [2 columns].