Bark improved allowing plants to inhabit drier environments. Support structures improved leading to the evolution of tall trees. Root systems and vascular tissue improved to allow the plants to obtain water and nutrients more efficiently. This increased erosion which increased sedimentation in the shallow shelf environments. Habitats started to shrink and continents started a drying trend as Pangea formed.
Brachiopods develop spines and heavier shells as sharks develop broad, flat teeth for crushing.
Slow moving Trilobites with weak shells begin to decline. Food gathering techniques improve. Insects appear in the middle Devonian and explode to over 400 forms by Pennsylvanian. Scorpions, cockroaches, winged insects, spiders all appear. By Late Paleozoic Osteichthyes and Chondrichthyes are the dominant classes.