A Forest Environment
The development of forests would have necessitated changes in habitat (from the ground to arboreal) for some animals. Evolving at this time were the first vertebrate animals which had four legs, a backbone and moist skins and were also carnivorous on the invertebrates. Among the invertebrates bristletails and springtails evolved and remain one of the most numerous of invertebrates with the most familiar being the silverfish. Silverfishes have clear but even more reduced segmentation consisting of a conspicuous head supporting compound eyes and antennae, a thorax bearing three pairs of jointed legs (a result of three segments being fused) and segmented abdomen which has lost its limbs but possesses three filaments at the extreme end. These animals breath much as millipedes do with a tracheae system, they copulate like scorpions do with the female walking over packets of sperm and taking them up into the genital pouch.