Triceratops horridus (Marsh 1889) Late Cretaceous ~70 mya was the last of the ceratopsians. This mount from an auction house may be a chimaera or a complete specimen. There is no museum number. This clade became quadrupedal, developed a large head crest and a variety of horn combinations. Note the curved ischium and the ilia extend laterally, provideing the hips a form of armor. The juvenile Triceratops (below) has shorter skull features.

Triceratops sp. juvenile (below) has an original reconstruction and a new one based on text measurements rather than scale bars.

Chasmosaurus belli (Lambe 1902, 1914; Late Cretaceous, up to 4.2m) is distinct from Triceratops in having short orbital horns and a heart-shaped shield lightened by large fontanelles (distinct from the upper temporal fenestrae). Large ridges strengthen the frill.

Chasmosaurus sp. (Currie et al. 2016, juvenile (below) is known from a complete articulated skeleton lacking only the forelimbs. The proportions are not so different than the adult, other than the shield, adding doubt to the earlier Triceratops reconstruction. The shield is small and the fontanelles are smaller. The sharp cheeks do not extend lateraly.

Currie PJ, Holmes RB, Ryan MJ and Coy C. 2016. A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1048348.

Lambe LM 1914. On Gryposaurus notabilis, a new genus and species of trachodont dinosaur from the Belly River Formation of Alberta, with a description of the skull of Chasmosaurus belli. The Ottawa Naturalist 27: 145-155

Marsh OC 1898. New species of Ceratopsia. Am J Sci, series 4 6: 92.

wiki/Chasmosaurus
wiki/Triceratops