How many non-avian dinosaur species existed? Figuring just the Mesozoic (251-65 my), average âlifespanâ for species is about 1 my., number of species at any moment as about for a specific class is about 4,000-8,000 species. So my estimate is about 500,000 to 1,000,000 species of non-avian dinosaurs existed during the whole of the Mesozoic. Of which only 1,250 valid species (0.125%-0.250%) have been discovered. Toss in avian-dinosaurs and include the Cenozoic and you get at least 1,500,000 species! Thatâs a lot of Dinosaurs!!! John Schneiderman John-schneiderman@cox.net Sent from Mail for Windows 10 |