in available oxygen This caused more predators to evolve so their prey also had to evolve quickly to adapt and survive in a world where they could be hunted and eaten Scientists believe most of the animals alive on Earth today descend from the creatures that evolved during the Cambrian explosion ARTHROPODS MOVE TO LAND Trilobites and sea scorpions are classified as part of a group of animals called arthropods Scientists split up the known animal kingdom into groups called phyla The animals in the Arthropoda phylum have segmented bodies jointed legs and hard exoskeletons that protect them like armor The Arthropoda phylum is further split into several different groups called classes Crustaceans such as crabs and lobsters make up one class Spiders are in the Arachnida class And insects make up the Insecta class Within each class are different orders For instance the order Lepidoptera within the insect class contains all the butterflies and moths Approximately 500 MYA the first plants made their way onto land Algae started to grow on shores taking root and becoming rigid enough to stand upright and collect more sunlight Algae continued to develop into green mosses ferns and horsetails These early plants provided homes and food for the first creatures that also moved from water to land The early land
CLASSIFICATION Honey Bee Apis mellifera DOMAIN Eukaryota This domain includes plants animals and fungi These organisms are grouped together because their cells each have a nucleus a cell structure that contains the DNA KINGDOM Animalia All animals including mammals and insects are in this group PHYLUM Arthropoda Organisms in this phylum have an exoskeleton and segmented bodies CLASS Insecta This class contains insects whose bodies have three segments the head thorax and abdomen They also have three pairs of legs that they use for walking ORDER Hymenoptera This order contains insects including ants bees saw flies and wasps FAMILY Apidae Bees make up this family GENUS Apis This family contains nine bee species that may all at times be called honey bees SPECIES mellifera Honey bees are the only domestic species of bee They are the only Taxonomic classification is the science of identifying living things grouping them together and naming them When this is done each organism is assigned a place in eight different categories ranging from domain the most general category to species the most specific category When the scientific name of an animal is given it includes the genus which is capitalized and the species which is not Honey bees are Apis mellifera Scientific names are often abbreviated after first use A. mellifera 9
explorers may also have been avoiding large predators such as sea scorpions that preferred to hang out in deeper water Arthropods were well equipped for life on land in prehistoric times Their exoskeletons helped protect them from the sun Their jointed legs propelled them onto land SPRINGTAILS Springtails may have been some of the earliest land dwellers These small wingless arthropods may have originally crawled out of the water to reproduce away from predators and to seek a hiding place in the algae Springtails got their name because of the taillike appendage they use for leaping They're so similar to insects that scientists used to believe they were closely related but recent DNA studies put them in their own order They probably made the transition from ocean to land before insects The evolution of insects occurred in four episodes or stages that happened over millions or even tens of millions of years The first episode of insect evolution was when the early insect ancestors which resembled modern bristletails from the order Archaeognatha evolved The second stage was when some insects evolved wings that can't fold such as those on dragonflies Later other insects evolved wings that could fold such as those 10
Butterflies develop through complete metamorphosis Caterpillars undergo a drastic transformation into their adult forms on cockroaches The fourth stage of evolution was the evolution of complete metamorphosis the transformation of the animal as it develops to an adult form One example of this is the transformation of caterpillars to butterflies Finally social groups developed For example ants or bees live and work together in groups to find food and rear their young Metamorphosis is a process that benefits insects by allowing them to have significantly different life stages to avoid competition for habitats and food sources within a species Not all insects use metamorphosis in the growth and development process and some only use incomplete metamorphosis However all animals with an exoskeleton must shed their skin to
