Something remarkable happened 160 million years ago. Three of the most diverse groups on the planet exploded in a simultaneous speciation event. Two of the groups were new at the beginning of the Cretaceous period, the last chapter in the age of dinosaurs. Flowering plants had just evolved from conifers and birds had just come on the scene as a compact, flying dinosaur. The third group , the insects, had already been around for 320 million years. However, they had not begun their total domination of the species list of the planet. The combination of these two flying animal groups and a plant group that sought a new, more efficient way to move pollen to a mate created the right conditions for speciation.
Creating a new species takes some dedicated snobbery. You have to avoid mingling with anybody that is not in the club, even though they are clearly similar to you. And you have to keep up the same consistent snobbery for hundreds, if not thousands, of generations. Isolation is not enough. You have to invest in different activities than the other cliques and those investments have to pay off by suiting you to a particular environment or source of food. Otherwise, your little break away group will be reeled back into the parent species as quickly as the peloton engulfs the leaders in the Tour de France. Flowers are really snobby. Instead of casting their pollen indiscriminately to the wind, they hold on to it and wait for the right shaped flying animal to come along! By investing in nectar and colors and scents, they attract a particular group of pollinators which, in turn, deliver pollen to other flowers of the same kind. The pollinators, too, become specialized and find themselves hanging out – and mating – with individuals attracted to the same flowers.
Much has been made of the coevolution of flowers and insects and , to a lesser extent, the coevolution of flowers and birds. Yet that cannot be the entire story of the Cretaceous speciation event. Some insect groups that first appeared during that time were butterflies, ants and grasshoppers. The latter two are not known for pollinating. Much of the speciation to occur within the birds would happen much later. The perching birds show up 120 million years after these events. In addition, the most abundant flowering plants- trees and grasses, still use the tried and true method of wind pollination. This is probably because, as dominant species, they could not support a big enough pollinator community to transfer all the pollen required to make seed on the massive scale that is required in deciduous forests and prairies.
In the end, this burst of creativity in the early Cretaceous created foods, activities and opportunities for flowering plants, insects and birds. These three groups are the focus of my ongoing study of the lopsidedness of evolution. Why do some groups produce so many species and others so few? Next time we will explore the insects and look at whether the massive and unprecedented branching that occurred among the beetles had its roots in the earliest branching of the class.