How so ? Neither water-based, nor land-based dinosaurs are actually extinct. They've (mostly) shrunk a lot, yes, but that's about it. Location and size protecte

How so ? Neither water-based, nor land-based dinosaurs are actually extinct. They've (mostly) shrunk a lot, yes, but that's about it. Location and size protected both kinds of dinosaurs, land-based or sea-based. All birds are dinosaurs (in the same sense that humans are apes). Hell, you've probably eaten a dinosaur egg this week. And the water-based dinosaur descendants are very well known and the inspiration for how dinosaurs now look in musea, the crocodiles, when we're not actually sure whether crocs or chickens looked more like land based dinosaurs. http://www.smithsonianmag.com/science-nature/Dinosaurs-Living-Descendants.html http://www.smithsonianmag.com/science-nature/Dinosaurs-Livin... Large animals go extinct on a regular basis. The reason animals become big is for efficiency, and so often a prelude to extinction (of that particular branch). A rat is much more efficient (work/energy) than an insect. A cat is (a lot) more efficient than a rat or a mouse. Cows and other large mammals are unbeatable when it comes to the amount of energy a kilogram of cow tissue requires to stay alive. But there's usually a reason animals become efficient, and that reason is that their methods of gathering energy are actually becoming unusable, and so energy available to the species is lowering. So the species reduces in numbers, and the physical size of individuals grows. Increased efficiency only happens out of necessity, and if it can't turn the tide, the next step is extinction ... And yes, humans definitely count as large animals. I wonder if we're an exception.