The insects of the early Mesozoic are represented by few fossils although it is evident some new forms were becoming established. The warm climates prevailing throughout much of the world appear to have been a favorable factor in the progress of insect life. In addition to the older cockroach and dragon-fly types may be mentioned the arrival of grasshoppers, cicadas, caddis-flies, beetles, and ants. Several hundred species are found in Jurassic rocks, and by the end of the Cretaceous period most of the insect families now known to us were probably in existence. The record is seriously obscured by the erosion of rocks which so frequently marks the end of a period, also by the small size of the subjects, and by the exceptional conditions required for the production of such delicate fossils. Among the last of the familiar insects to appear were the bees and butterflies. These evidently came in with the more advanced types of flowering plants that produce the nectar on which many insects feed. It is probable, too, that without the arrival of these insects and their service in the pollination of flowers, the floras of today would be rather different from what they are. EXTINCT BIRDS It is not surprising to find that birds made their first appearance in the Mesozoic era, for of all animals they are most like the reptiles as a class. Feathers are about the only dependable characteristic of the entire group, nearly every other feature being matched by some reptilian creature of great antiquity. The nesting habit, which includes care of the young as well as the eggs, is a matter of progress which relates to flight and to warmer body temperature. It appears to have been developed by forest-dwelling types living among trees and nesting there in comparative safety from enemies prowling on the ground.