What is with you, science?
First you kill off the planet Pluto, then you decide that protons are smaller than we thought, and now that the triceratops is actual the juvenile form of the lesser-known torosaurus. What gives?
Progress, my friends. Knowledge. But sometimes with new discoveries come the fact that, tear, adult triceratops, well...they don't exist. Or, they don't exist as triceratops like we think of them today. Thank goodness that Cera (the bossy one from The Land Before Time) will never really get old.
(speaking of, they're on Land Before Time XIII (that's 13) and according to Wikipedia includes such characters as Loofah and Doofah. No joke)