Over ninety-nine percent of the insect species that have been described by scientists are placed in a group (Infraclass) called the Neoptera. These insects (including flies, bees, true bugs and beetles, for example) have the ability to fold their wings down flat against their abdomens.

Damselflies and dragonflies belong to a smaller group, the Palaeoptera, which lack the added hinge which allows the Neoptera to fold their wings flat. The group Palaeoptera includes one other order of extant insects, the Ephermeroptera, or mayflies, and several orders of extinct insects known only from their fossils.

Dragonflies hold their wings out to the side when resting, somewhat like the pages of an open book. Damselflies and mayflies hold their wings together perpendicular to their thorax like little sails.

The ability of the Neoptera to fold their wings flat allowed them to radiate into many different habitats that the Palaeoptera were unable to use because of their protruding wings. This advantage may account for the fact that the Neoptera so greatly outnumber the Paleaoptera today.

Fossil Palaeoptera, including the extinct order Protodonata (which shares many of the characteristics of modern Odonata), have been found from Upper Carboniferous strata of 300 million years ago. Some of these insects had astounding wingspans of 700 mm (27 inches). Order Odonata first appeared in the Triassic period, but became much more diverse in the Jurassic (145-210 million years ago).

Because they lived near water, many specimens of Odonata have been preserved as fossils, and there is a long and rich fossil history. Interestingly, many important fossil Odonata have been taken from the Permian beds of Kansas and Oklahoma.

In addition to the suborders Anisoptera and Zygoptera, many entomologists recognize a third suborder, the Anisozygoptera. This was a very diverse suborder of Odonata during the Jurassic. While it contains many extinct species, there are only two living species in the suborder, one from Japan and a second from the Himalayas. These strange insects have bodies like dragonflies, with wings that have many characteristics in common with damselflies.

Reference 11 contains information and pictures of fossil insects and is a good starting place for those who want to learn more about the fossil record and the evolution and diversity of damselflies and dragonflies.