It is, however, not continuous, but a step function. Although these are different for the two coasts the stepwise diversity curves are the same. The cause must be something really general. Solar radiation was considered. Analyses of sea temperatures showed that solar radiation caused very similar ocean temperature patterns latitudinally on both coasts.
Temperature is a very important factor and correlates with diversity.
Warm temperature anomalies, above the mean annual temperature at a given latitude, promote higher nutrient levels and hence higher diversity. Until now, most workers in paleontology have not addressed these kinds of questions. To many they are issues that have been accepted for so long that they seem to be indisputable. But, like so many times in the past, that which seems obvious turns out, on close examination, to be more complicated than anyone originally thought. Dave has plenty of knotty problems, but clearly loves the challenge of them all.