Changchunsaurus parvus (Zan et al. 2005; Early Cretaceous, JLUM L0403-j-Zn2; 1m) originally considered a basal ornithopod, Changchunsaurus has been allied to Jeholosaurus and later to Haya. Here it nests with Dryosaurus as the base of the Ornithopoda, close to Hexinlusaurus at the base of the Ceratopsia.

The ribs appear to be wider than deep with an extensive lumbar area. The premaxilla is long and toothy.

Dryosaurus altus (originally Laosaurus, Marsh 1878, 1894, Galton 1977) Late Jurassic, 14 feet (4.3 m) long (as a juvenile), is a basal iguanodont, basal to the duckbill dinoaurs as well. A biped and herbivore with inset teeth likely provided with cheeks to prevent spill out.

Tenontosaurus tilletti (Ostrom 1970, Early Cretaceous, 6-7m length) was a transitional taxon between Late Jurassic Dryosaurus and Late Cretaceous large duckbills like Edmontosaurus.

Edomontosaurus annectens (Lambe 1917, 1920) Late Cretaceous (12m) long is the classic dukbill dinosaur. The dentary and maxillary teeth form a battery of grinding surfaces. The hind limbs are robust with a thick fibula. Digit 1 is absent.

Butler RJ, Jin L-Y; Chen J and Godefroit P 2011. The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north-eastern China. Palaeontology 54 (3): 667–683. doi:10.1111/j.1475-4983.2011.01046.x.

Jin L, Chen J, Zan S-Q, Butler RJ and Godefroit P 2010. Cranial anatomy of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, northeastern China. Journal of Vertebrate Paleontology 30 (1): 196–214. doi:10.1080/02724630903412372.

Lambe LM 1917. A new genus and species of crestless hadrosaur from the Edmonton Formation of Alberta. The Ottawa Naturalist 31 (7): 65–73. Retrieved 2009-03-08.

Lambe LM 1920. The hadrosaur Edmontosaurus from the Upper Cretaceous of Alberta. Memoir 120. Department of Mines, Geological Survey of Canada. pp. 1–79. ISBN 0-659-96553-4.

Marsh OC 1894. The typical Ornithopoda of the American Jurassic. American Journal of Science, series 3 48:85-90.

Ostrom JH 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Peabody Museum Bulletin 35:1–234.

Thomas DA 2015. The cranial anatomy of Tenontosaurus tilletti Ostrom, 1970 (Dinosauria, Ornithopoda). 2015. The cranial anatomy of Tenontosaurus tilletti Ostrom, 1970 (Dinosauria, Ornithopoda). Palaeontologia Electronica 18.2.37A: 1-99
palaeo-electronica.org/content/2015/1178-skull-of-tenontosaurus

Tenent J 2013. Osteology of a Near-Complete Skeleton of Tenontosaurus tilletti (Dinosauria: Ornithopoda) from the Cloverly Formation, Montana, USA Masters thesis, U of Manchester, England.

Zan S-Q, Chen J, Jin L-Y, Li T 2005. A primitive ornithopod from the Early Cretaceous Quantou Formation of Central Jilin, China. Vertebrata PalAsiatica (in Chinese and English) 43 (3): 182–193.

wiki/Changchunsaurus
wiki/Dryosaurus
wiki/Tenontosaurus
wiki/Edmontosaurus