[Illustration: Fig. 9.--Pelves of Dinosaurs illustrating the two chief types (Saurischia, Ornithischia) and their variations.]
Recent researches upon Triassic dinosaurs, especially by the distinguished German savants, Friedrich von Huene, Otto Jaekel and the late Eberhard Fraas, and the discovery of more complete specimens of these animals, also clear up the true relationships of these primitive dinosaurs which have mostly been referred hitherto to the Theropoda or Megalosaurians. The following classification is somewhat more conservative than the arrangement recently proposed by von Huene.
ORDER SAURISCHIA Seeley. Suborder _Coelurosauria_ von Huene (=Compsognatha Huxley, Symphypoda Cope.) Fam. Podokesauridæ Triassic, Connecticut. " Hallopodidæ Jurassic, Colorado. " Coeluridæ Jurassic and Comanchic, North America. " Compsognathidæ Jurassic, Europe. Suborder _Pachypodosauria_ von Huene. Fam. Anchisauridæ Triassic, North America and Europe. " Zanclodontidæ } " Plateosauridæ } Triassic, Europe.* Suborder _Theropoda_ Marsh (=Goniopoda Cope) Fam. Megalosauridæ Jurassic and Comanchic. " Deinodontidæ Cretacic. " Ornithomimidæ Cretacic, North America. Suborder _Sauropoda_ Marsh (=Opisthocoelia Owen, Cetiosauria Seeley.) Fam. Cetiosauridæ } " Morosauridæ } Jurassic and Comanchic. " Diplodocidæ } Order ORNITHISCHIA Seeley (=Orthopoda Cope, Predentata Marsh.) Suborder _Ornithopoda_ Marsh (Iguanodontia Dollo) Fam. Nanosauridæ Jurassic, Colorado. " Camptosauridæ } " Iguanodontidæ } Jurassic and Comanchic. " Trachodontidæ (=Hadrosauridæ), Cretacic. Suborder _Stegosauria_ Marsh. Fam. Scelidosauridæ } Jurassic and Comanchic. " Stegosauridæ } " Ankylosauridæ (=Nodosauridæ), Cretacic. Suborder _Ceratopsia_ Marsh. Fam. Ceratopsidæ Cretacic.
* Regarded by Dr. von Huene as ancestral respectively to the Theropoda and Sauropoda.
[Footnote 2: If some vast catastrophe should today blot out all the mammalian races including man, and the birds, but leave the lizards and other reptiles still surviving, with the lower animals and plants, we might well expect the lizards in the course of geologic periods to evolve into a great and varied land fauna like the Dinosaurs of the Mesozoic Era.]
[Footnote 3: The ancestral types have four complete toes, but in the true Theropoda the inner digit is reduced to a small incomplete remnant, its claw reversed and projecting at the back of the foot, as in birds.]