Figure 2. Phylogeny of Dinosauria, showing the relationships among ornithischians (left) and saurischians (right). Thickened internal branches are scaled to reflect the number of supporting synapomorphies (scale bar equals 20 synapomorphies). Phylogenetic structure and internal branch lengths are based on minimum-length trees from maximum-parsimony analyses of approximately 1100 characters under delayed character-state optimization (Table 1). The evolution of hadrosaurids within Ornithopoda (nodes 11 through 18) and birds within Tetanurae (nodes 46 through 57) provide the best examples of sustained skeletal transformation. Numbered nodes are listed here, with normal and bold text indicating stem- and node-based taxa, respectively (88): 1, Ornithischia; 2, Genasauria; 3, Thyreophora; 4, Eurypoda; 5, Stegosauria; 6, Stegosauridae; 7, Ankylosauria; 8, Nodosauridae; 9, Ankylosauridae; 10, Neornithischia; 11, Ornithopoda; 12, Euornithopoda; 13, Iguan- odontia; 14, Ankylopollexia; 15, Styracosterna; 16, Hadrosauriformes; 17, Hadrosauroidea; 18, Hadrosauridae; 19, Marginocephalia; 20, Pachycephalosauria; 21, Pachycephalosauridae; 22, Pachycephalosaurinae; 23, Ceratopsia; 24, Neoceratopsia; 25, Coronosauria; 26, Ceratopsoidea; 27, Ceratopsidae; 28, Saurischia; 29, Sauropodmorpha; 30, Prosauropoda; 31, Plateosauria; 32, Massospondylidae; 33, Plateosauridae; 34, Sauropoda; 35, Eusauropoda; 36, Neosauropoda; 37, Diplodocoidea; 38, Macronaria; 39, Titanosauriformes; 40, Somphospondyli; 41, Theropoda; 42, Neotheropoda; 43, Ceratosauria; 44, Ceratosauroidea; 45, Coelophysoidea; 46, Tetanurae; 47, Spinosauroidea; 48, Neotetanurae; 49, Coelurosauria; 50, Maniraptoriformes, 51, Ornithomimosauria; 52, Ornithomimoidea; 53, Tyrannoraptora; 54, Maniraptora; 55, Paraves; 56, Deinonychosauria; 57, Aves; 58, Ornithurae; 59, Ornithothoraces.