Extinction of the dinosaurs: A 1982 understanding

The objective record appears to be that the dinosaur fauna of the latest Maastrichtian (i.e., latest Cretaceous) was chiefly (and perhaps exclusively) restricted to the Western Interior Seaway of the United States and southern Canada and included fewer than 20 species distributed among approximately 15 genera and 10 families. In the late Maastrichtian, as has been known for many years, sea level went down by 150 to 200 m in the western interior. The interior seaway (along which the dinosaurs were living) dried up and seasonality increased and habitable area was reduced as widespread flood plains yielded to uplifted, restricted basins. This occurrence of a gradually changing ecology correlated with animal extinction conforms to the observed pattern characteristic of many other times in the fossil record. If this pattern applies to dinosaurs as well, then the extinction of the dinosaurs is neither necessarily nor reasonably attributable to any extraterrestrial event. In addition, it appears that the magnitude of the extinction is greatly over estimated because a very small number of species and genera were actually responsible for the familial extinctions.