As described above, Scannella had argued in 2010 that Nedoceratops should be considered a synonym of Triceratops.

Most other ceratopsids had large parietal fenestrae, openings in their frills, but those of Triceratops were noticeably solid, [34] unless the genus Torosaurus represents mature Triceratops individuals, which it most likely does not. In the first attempt to understand the many species, Richard Swann Lull found two groups, although he did not say how he distinguished them. Since there were many more specimens in the first group, she suggested that this meant the two groups were two species. The metatherians are represented by the alphadontids Alphadon, Protalphodon, and Turgidodon, the pediomyids Pediomys, [104] Protolambda, and Leptalestes, [106] the stagodontid Didelphodon, [104] the deltatheridiid Nanocuris, the herpetotheriid Nortedelphys, [105] and the glasbiid Glasbius.As dinosaur fans know, Triceratops and Tyrannosaurusrex occupied the same ecosystem—the marshes and forests of western North America—about 65 million years ago, just before the K-T extinction that wiped out the dinosaurs.

A partial Triceratops fossil collected in 1997 has a horn that was bitten off, with bite marks that match Tyrannosaurus. It is likely Triceratops' horns and frill were used in combat against other Triceratops, as well as for visual display (mating, communication and species recognition), according to a 2009 PLOS ONE study. The tyrannosaurids from the formation are Nanotyrannus and Tyrannosaurus, although the former is most likely a junior synonym of the latter.They may have eaten a variety of palms, ferns, cycads, and other plants available at that time period. The two brow horns appear to have twisted and lengthened as a Triceratops aged, according to a 2006 study in the journal Proceedings of the Royal Society B. Analysis of the endocranial anatomy of Triceratops suggest its sense of smell was poor compared to that of other dinosaurs. They suggested that such metabolisms may have been common for ornithischian dinosaurs in general, with the group evolving towards ectothermy from an ancestor with an endothermic (warm blooded) metabolism.

The first named fossil specimen now attributed to Triceratops is a pair of brow horns attached to a skull roof that were found by George Lyman Cannon near Denver, Colorado, in the spring of 1887. Scannella's Triceratops specimen with a hole on its frill, they argued, could represent a diseased or malformed individual rather than a transitional stage between an immature Triceratops and mature Torosaurus form.Dental morphology and body-size patterns reveal extinction selectivity and immigrant-fueled ecospace filling". This contains fibroblasts that play a critical role in wound healing and is capable of rapidly depositing bone during remodeling.