The animal kingdom as covered here at factzoo, includes a great part of the web of life but excluding plants, fungi and micro-organisms. Life began as slimy organisms floating and jerking around in the liquid matter of the earth. The first species of fish developed backbones at least 440 million years ago. Then, 360 million years ago or earlier some aquatic species made the transition from swimmers to land crawling creatures – amphibians. The early amphibians largely died out and gave rise to the dominant animals of the day, the reptiles’ ancestors, dinosaurs. Then, those reptile forms themselves largely died out and gave rise to mammals and birds which dominate the land and sky today. Meanwhile of course, the invertebrates (insects and others) and fish continued their paths of evolution with the surviving lines of amphibians and reptiles.