At https://archaeologynewsnetwork.blogspot.com/2019/11/dinosaur-skull-turns… … a dinosaur skull unearthed in 2015 is causing a problem. It was the skull of a styracosaurus, complete with horns. The differences in the skull's left and right profiles are so extreme they appear to belong to two different animals – but clearly aren't …
… the same story is at Phys Org at https://phys.org/news/2019-11-dinosaur-skull-paleontology-assumptions.html … and was published in Cretaceous Research (2019) – see https://doi.org/10.1016/j.cretres.2019.104308 … and it seems that some divisions of dinosaurs, previously thought to represent different species, or varieties of the same species, will have to be re-evaluated.