Your average reconstruction of the Mesozoic looks like the Serengetti Plains of the modern day but with dinosaurs, not lions and zebras. This kind of reconstruction is the kind we normally see, and I think that it colors our view - I think that we have brought the present to the past. We assume there as many species and individuals of dinosaurs wandering around in the Mesozoic as there are mammals in the present day. In truth, there is an enormous amount of evidence that suggests that this is not so. Rather, if you got out of your time machine, you would be lucky to see perhaps, one (small) herd of dinosaurs in a day.

If you actually do a head count of species, there are about 370 species of dinosaurs that are known, and at the most outrageous potential estimate, about 1,500 species of terrestrial dinosaurs are predicted to exist in the Mesozoic. That guess is about 1,500 for a period of 165 million years. That is about eight dinosaur species per million years.

Now suppose we do a similar calculation on the mammals of the last 65 million years, the Tertiary. The estimate runs between 80 and 180 species per million years (depending on source). This is a sharp contrast - there are really very, very few terrestrial dinosaurs. And, what is really cute is, if you actually dissect the dinosaurs' specific diversity, 50% of their diversity occurs in the last 20 million years of the Cretaceous - leaving the other 50% to span 140 million years. This is a weird ecosystem. This is unlike anything we presently know. It is a completely different story. Added to this, if we look at the early history of dinosaurs, not only are dinosaur species rare, but individual dinosaurs are rare. The biggest herd known until the late Cretaceous, includes 20-25 individuals. Until the Late Cretaceous, dinosaurs are low in specific and individual diversity.

What are insects doing during this time period? What about those other plant predators? Well, they diversified (particularly in the Pennsylvanian) and they just keep diversifying. The radiation of seed plants in the Triassic spurs a diversification in feeding types -- the number of different ways of feeding using different mouth parts. These guys learned how to feed on pteridophytes, these guys learned how to feed on seed plants. Not a problem! You note that the appearance of the angiosperms (at about the Late Cretaceous) has little effect; the insects "see" angiosperms as simply another seed plant. The appearance of angiosperms doesn't necessarily spur a diversification of types of feeding. So the insects are there, plodding along, diversifying, and taking advantage of plants.

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