I’m not an expert, nor even a well-informed layman, but my understanding is they argue that fossilisation is extremely rare, rare enough for a civilisation that

I’m not an expert, nor even a well-informed layman, but my understanding is they argue that fossilisation is extremely rare, rare enough for a civilisation that may have only lasted a few hundred years to slip through unnoticed. See, for example, https://www.nature.com/articles/d41586-021-00984-2 https://www.nature.com/articles/d41586-021-00984-2 — only 32 adult T. rex have been found [as of the date of the article], even though the species existed for two million years or so. Are they overstating things?