No one, either in the nineteenth century or the twentieth, has ever built a persuasive case proving that dinosaurs as a whole were more like reptilia… - Robert T. Bakker

When the dinosaurs fell at the end of the Cretaceous, they were not a senile, moribund group that had played out its evolutionary options. Rather they were vigorous, still diversifying into new or­ders and producing a variety of big­brained carnivores with the highest grade of intelligence yet present on land.

Twentieth-century paleontologists have fallen into the bad habit of reconstructing the dinosaurs' life functions by using crocodiles as a living model. But the earliest researchers of the nineteenth century proved beyond a doubt that the dinosaurs' powerful hind limbs must have operated like the limbs of gigantic birds.

Duckbills were supposedly croc-style swimmers, moving by strong, easy, side-to-side flexures of their tail. Therefore, the optimal design would feature vertical tail spines. But duckbill spines all slanted strongly backward, exactly as in land-living lizards, not in swimmers.
Another problem in the duckbill's swimming equipment lies in the profile of the tail. The deepest part of the croc's tail is close to the end, because the end swings through a wider arc than does the base in moving side to side. Thus the tail is deepest where it can do the most good in pushing against the water. All powerful tail-scullers have such deep tail ends. But duckbill tails were deepest at the hips and become progressively narrower from top-to-bottom toward the tip - another caudal feature nearly totally maladapted for its primary function.