While later Cretaceous dinosaurs are smaller than their predecessors, they are still huge. The big "brontosaur" guys average somewhere between 10 and 20 or 30 tons each. The ornithischians of the later Cretaceous are running one to 10 tons each. But, if you compare that to the average size of the mammalian herbivores, particularly the Serengetti savanna and the Gabon rainforest these dinosaurs are still huge.

There is another feature of interest. Not only are ornithischia more speciose, they are also turning up much greater in numbers as individuals. Other sites have revealed other great herds of ornithischia, as for example ceratopsians which Bob Bakker calls "the cockroaches of the Cretaceous", they are so common. We haven't seen this before in the Mesozoic - I suggest that plants have done it again. The radiation of angiosperms, the all-purpose, do anything, go-anywhere plant, appears to have underwritten an explosion in ornithischian dinosaur diversity. A further circumstantial line of evidence comes from the Late Cretaceous of western North America where duckbilled and horned dinosaurs tend to be associated with floras containing angiosperms, while large sauropods such as Alamosaurus, are associated with conifer dominated forests. Again, it appears that the flora is driving the terrestrial vertebrate evolution.

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