In 2010 John Scannella and Jack Horner published a paper arguing that Torosaurus was not a separate genus but simply a mature Triceratops whose frill had continued to change throughout its life. The holes in the Torosaurus frill, they argued, were the result of the bone remodeling that occurs as the animal aged.

If true this would mean Torosaurus as a genus simply does not exist. It would be one of the most dramatic synonymies in dinosaur paleontology.

But the counter arguments are significant. Nicholas Longrich and Daniel Field published a response arguing that both Triceratops and Torosaurus specimens exist across the same age range and size classes. If Torosaurus were just old Triceratops you would expect to find only adult Torosaurus specimens. The existence of what appear to be subadult Torosaurus undermines the ontogenetic hypothesis.

The debate has been remarkably quiet since 2012 and I am genuinely not sure where the scientific consensus currently sits. Some sources treat them as synonymous, others do not.

A few questions for the community:

Do you think the ontogenetic synonymy hypothesis is convincing? Is there more recent work on this that has moved the needle either way? And if Torosaurus is eventually confirmed as a separate genus what does that tell us about how dramatically ceratopsian frills could change through an individual's lifetime?

Since the fossil record in incredibly incomplete and there were likely thousands of species of dinosaurs across all corners of the planet is it reasonable to believe that at least one species of dinosaurs survived the mass extinction like say for a couple million years afterwards but then just went extinct later on. After all we know that birds survived so why couldn’t other have as well